Basement is freezing due to HVAC - thoughts/fixes?

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sperry8
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Basement is freezing due to HVAC - thoughts/fixes?

Post by sperry8 »

Hello all,

Looking for some HVAC advice.

Background:
-New construction (2022) holiday home in the Northeast.
-Finished 1,000 sq ft basement, 1,700 sq ft main floor with a LR with 17' cathedral ceilings.
- A manual J report was completed prior to installation (and a blower test was completed after).
-Rheem R410A 4-Ton 16 SEER Condenser M# RA1648AJ1NA. I do not have a split unit (so single Rheem manages the whole house).
-The home has a 2 car garage (attached to the basement). From the garage you can access the basement and the HVAC room (via separate doors).
-The basement is underground although there are 2 egress windows. The garage side of the basement has direct street access - the land is on a slope.
-The basement was has spray foam insulation (walls and ceiling). The floor underneath the basement flooring has Dupont Styrofoam Tongue and Groove insulation. Here is a photo of that install https://ibb.co/28xRVSs which also gives you a basic visual of the basement layout (and how the garage is open but the rest of the basement is underground).
-The Nest temperature controller is in the main floor LR (with 17' cathedral ceilings). Due to placement, obv the rest of the home gets slightly colder than the LR (which is necessary as the LR gets quite warm otherwise).

Issue
-My issue is the main floor is ~10° higher than the basement, so when it is 74° on the main floor, the basement is 64°. Which, imo, makes the basement unusable. The original installer said this was "normal".
-Here is a link to the temperature differences (you can see how the garage is also freezing and yet the garage doors go to the outside).
https://ibb.co/CQNVYCq
-Note the the only air return in the house is on the main floor (the basement has no return).
-I have closed the dampers to the basement supply vents and taped silicone over them to stop the cold air from blowing during the summer (which offers no help at all).
-I run space heaters all summer (yes, even in the dead of August) to make the rooms usable. I don't run them constantly, but turn them on an hour before we want to use the gym or play room.
I took a temperature gun and couldn't find any colder spots in the basement than the rest. The ground was ~1-2° less than the walls and ceiling (which seems normal).

Thoughts?
-Would it help "balance" the air flow if I added a basement return?
-If not, is there anything else I can do short of adding a mini split system in the basement to heat it during the summer (~$15k for 2 units installed)?
-Why is the garage also so cold (and humid)? If it's that humid (because it's that humid outside) wouldn't this mean air is getting into it and thus shouldn't the temps there be higher (in summer) and colder (in winter)? Perhaps the HVAC room is blasting cold air out of it into the garage (the door to it has at least 1" between it and the floor).

I truly appreciate any thoughts. It has been a few summers now and I'm at wits end trying to figure it out how to mitigate this.
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sleepy06
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by sleepy06 »

1. Last home with walkout basement we had a similar problem. We were able to install a large minisplit that could service the whole basement as it was just a large room. Worked great.
2. This home, we have a dedicated standard unit to walkout basement.
inverter
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by inverter »

Closing the dampers will just restrict overall airflow so I would undo that.

Did you say they spray foamed the ceiling of the basement? That could be part of the problem if so… heat isn’t migrating within your building envelope, as the basement would be thermally isolated.

A couple of ideas if so would be:

1. Install a return in the basement so air migrates from the first floor to the basement

2. Remove ducting in the basement and install separate mini-split system
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whodidntante
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by whodidntante »

You might be leaking a lot of cold air out of the ductwork. Finally, a proper use for duct tape.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by inverter »

whodidntante wrote: Sun Jun 02, 2024 8:30 pm You might be leaking a lot of cold air out of the ductwork. Finally, a proper use for duct tape.
Duct tape is actually not meant to be use on ducting.

https://tapeuniversity.com/industry/hva ... -ductwork/
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sperry8
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by sperry8 »

sleepy06 wrote: Sun Jun 02, 2024 8:17 pm 1. Last home with walkout basement we had a similar problem. We were able to install a large minisplit that could service the whole basement as it was just a large room. Worked great.
2. This home, we have a dedicated standard unit to walkout basement.
So you used the mini split to heat the basement while you simultaneously cooled the remainder of the house? Just seems so weird to me (especially in summer).
inverter wrote: Sun Jun 02, 2024 8:26 pm Closing the dampers will just restrict overall airflow so I would undo that.

Did you say they spray foamed the ceiling of the basement? That could be part of the problem if so… heat isn’t migrating within your building envelope, as the basement would be thermally isolated.

A couple of ideas if so would be:

1. Install a return in the basement so air migrates from the first floor to the basement

2. Remove ducting in the basement and install separate mini-split system
Yes, I'm pretty sure they spray foamed the ceiling before we closed it up (and there is insulation below that too). So that could create the thermal isolation you describe. It'd be easy enough to create a return directly back into the unit (so a basement return going right into the Rheem). Would that meet your recco? Or are you suggesting a jump (sort of a hole in the basement ceiling somewhere to the main floor just allowing more airflow?
(btw - there is a stairway from the basement to the main floor and the air can get under that door to the main fl. You can feel it happening. So it's not full isolation). But maybe a separate return is necessary to increase airflow.

Removing the ducting is a huge job (as the basement is finished). Further it is the only ducting (the main floor has floor supply) so the ductwork serves the main floor and basement (the basement has ceiling supply). So there is just one duct run that has two openings (top and bottom).

I realize closing the dampers is restricting airflow... but there are too many. I suppose I could close up a few permanently and leave just a few open.
whodidntante wrote: Sun Jun 02, 2024 8:30 pm You might be leaking a lot of cold air out of the ductwork. Finally, a proper use for duct tape.
How can I check for this? I used the temperature gun to check the ductwork and it was the same temps as the remainder of the walls (w/o ducts).
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snackdog
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by snackdog »

Our basement is chilly as well. We put a fan at the base of the stairs and attach a smart plug in July-Sept. If it gets over 80F outside, the fan comes on an blows cold air into the kitchen during the afternoon. Works ok.

We also have a damper for half the basement, but leave it half open. HVAC guy said not a good idea to close it completely and have no air to the basement. You need some circulation down there.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by whodidntante »

sperry8 wrote: Sun Jun 02, 2024 8:41 pm
whodidntante wrote: Sun Jun 02, 2024 8:30 pm You might be leaking a lot of cold air out of the ductwork. Finally, a proper use for duct tape.
How can I check for this? I used the temperature gun to check the ductwork and it was the same temps as the remainder of the walls (w/o ducts).
I like to use a moistened finger. Hairy arms work too.

A temperature gun probably won't help. The air should be roughly the same temperature as the duct.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by Gearheaddd »

You want to try and pull the air out of the basement and mix it with the air circulating throughout the house. If done correctly it should dehumidify the basement air and even save money on a/c since you’ll be introducing more cold air into the mix.

You should be able to add a large, adjustable register to the furnace return plenum that, when open, will pull in basement air, run it over the evaporator coils to dehumidify it and send it throughout the upper living area.

https://www.homedepot.com/p/TruAire-18- ... /203313490

You may need to experiment a bit with closing off basement registers and possibly add a dehumidifier to the basement if it’s too damp ( a dehumidifier will also help raise the basement temperature a bit). Initially leave the door to the basement open to see if you need to add a simple register or two in the floor between the upper living space and basement to allow better circulation. Finally, you need a thermostat which allows you to set your blower on “circulate” which will cause the air to move throughout the basement and upper living area for 30% or so throughout the day regardless of whether the system is calling for cooling.

I live in the northeast and have a similar setup which works very well using this method.
Last edited by Gearheaddd on Sun Jun 02, 2024 9:07 pm, edited 1 time in total.
bobn60014
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by bobn60014 »

Somewhat normal here in the Chicago area. We found a dehumidifier really helped.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by id0ntkn0wjack »

Am I correct that the 74F upper /64F lower temps are summer temps?

Also, what percentage of your main floor southern exposure is glass?

It sounds like your basement is essentially a Yeti cooler and being below grade would likely trend towards ground temperature.

I’m a bit surprised that your HVAC contractor would recommend/design a single zone 2700sf system and, no, it’s not “normal” to have a 10 degree delta between upper and lower floors in new construction.

There are too many variables to diagnose/resolve via an internet forum. Might be worth locating an energy efficiency auditor to give you unbiased options.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by z0r »

adding a basement return should help yes. it should be greater than or equal to the basement supply registers. if you don't have basement supply registers and your goal is to have it fully conditioned, add those also

once you have the basement return then you can set your thermostat to run in fan only mode on some schedule to get air mixing and average out the house. if you're lucky enough to have a multi speed air handler (didn't check your part #) some people will even run at the lowest speed 24/7 . 4 tons is a lot, yeah you had a manual j, but it's still a lot for just AC. is it a heat pump - maybe it was sized for heating? in the northeast a heat pump would normally be sized for heating and could be 2x bigger than it needs to be for cooling so you won't get much air mixing in the summer without a way to run fan only

a more extreme measure is to install a dedicated "anti stack" duct to take air from the highest practical point in the house and blow it to the lowest point (separate from your regular ductwork), plus some kind of return transfer grille. you can run this with an efficient fan 24/7 so it could only take a few tens of watts. it would be like a supercharged version of running the overall system as fan only, it can counteract your stratification directly
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by j.click »

HVAC Pro informed me that an easy partial mitigation is to keep blower fan 'on' all the time and not cycle. Less stress on motor than on/off cycles and helps distribute overall house air better. Hope this helps....
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by Jack FFR1846 »

Our home is basement with 7' ceilings, but all open, nothing finished, no sheet rock except over the furnace. First floor is normal. 2nd floor cathedral ceilings where roof is cape with dormer for the entire south side. I can equalize the entire house simply by switching the fan from run with the AC to on. This circulates air through the system from both floors. Our ducts are big enough and insulated so while the basement stays cool, I'd say it's maybe 3-5 degrees colder than the first floor. We have no ducts at all in the basement.

So in short, turn the fan switch to "ON".
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by firebirdparts »

The earth is about 50 degrees, so your best bet is to take advantage of that by moving more air. Make sure air is getting upstairs from the basement whether you put a return in or not, and then leave the fan on all the time. You could put a return in the basement but really you need the opposite. You need to pump air from up to down without cooling it.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by galving »

sperry8 wrote: Sun Jun 02, 2024 7:59 pm Hello all,

Looking for some HVAC advice.

Background:
-New construction (2022) holiday home in the Northeast.
-Finished 1,000 sq ft basement, 1,700 sq ft main floor with a LR with 17' cathedral ceilings.
- A manual J report was completed prior to installation (and a blower test was completed after).
-Rheem R410A 4-Ton 16 SEER Condenser M# RA1648AJ1NA. I do not have a split unit (so single Rheem manages the whole house).
-The home has a 2 car garage (attached to the basement). From the garage you can access the basement and the HVAC room (via separate doors).
-The basement is underground although there are 2 egress windows. The garage side of the basement has direct street access - the land is on a slope.
-The basement was has spray foam insulation (walls and ceiling). The floor underneath the basement flooring has Dupont Styrofoam Tongue and Groove insulation. Here is a photo of that install https://ibb.co/28xRVSs which also gives you a basic visual of the basement layout (and how the garage is open but the rest of the basement is underground).
-The Nest temperature controller is in the main floor LR (with 17' cathedral ceilings). Due to placement, obv the rest of the home gets slightly colder than the LR (which is necessary as the LR gets quite warm otherwise).

Issue
-My issue is the main floor is ~10° higher than the basement, so when it is 74° on the main floor, the basement is 64°. Which, imo, makes the basement unusable. The original installer said this was "normal".
-Here is a link to the temperature differences (you can see how the garage is also freezing and yet the garage doors go to the outside).
https://ibb.co/CQNVYCq
-Note the the only air return in the house is on the main floor (the basement has no return).
-I have closed the dampers to the basement supply vents and taped silicone over them to stop the cold air from blowing during the summer (which offers no help at all).
-I run space heaters all summer (yes, even in the dead of August) to make the rooms usable. I don't run them constantly, but turn them on an hour before we want to use the gym or play room.
I took a temperature gun and couldn't find any colder spots in the basement than the rest. The ground was ~1-2° less than the walls and ceiling (which seems normal).

Thoughts?
-Would it help "balance" the air flow if I added a basement return?
-If not, is there anything else I can do short of adding a mini split system in the basement to heat it during the summer (~$15k for 2 units installed)?
-Why is the garage also so cold (and humid)? If it's that humid (because it's that humid outside) wouldn't this mean air is getting into it and thus shouldn't the temps there be higher (in summer) and colder (in winter)? Perhaps the HVAC room is blasting cold air out of it into the garage (the door to it has at least 1" between it and the floor).

I truly appreciate any thoughts. It has been a few summers now and I'm at wits end trying to figure it out how to mitigate this.
Your basement is isolated by the spray foam, and more recently by blocking the vents.
This prevents you from controlling the temperature and humidity. This is visible on the temp data you provided.

You can check for duct leaks, though it's unlikely that this would resolve your issue because you don't have a system that's capable of controlling both the upper floor and the basement independently.

There is no circulation from the upper floors to the lower floors. This prevents the 'system' from being well mixed.
It's likely better to set up a different unit for downstairs.

Good luck,
galving
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by Target2019 »

Your basement is an insulated cooler. However, there are probably a significant number of ways for A/C air to fall into the basement cooler. Your garage is affected in a similar way.

A return vent, sized properly, will restore some balance in the temperatures, floor to floor.

You also can find the routes through which cold air gets into the basement space, and remediate those. Maybe a temperature gun would help.

In our home we have two floors and a basement. There are two (2) HVAC systems, one for each floor. The basement has no vents or returns. There is one door to the basement. If I leave that door ajar, I can easily lower the temperature of the basement. When A/C is in use, though, it will run longer on both of the higher floors when that door is open.

What helped me to understand the complex situation was, think of your home as a box that is filling with cold air. If the floors are not isolated from each other, your systems are running to fill that space, and then the cooled or heated air can trigger your thermostat(s) to pause the HVAC.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by mpnret »

You sure that the basement installed HVAC unit isn't blasting cold air into the downstairs space from somewhere else other than the supply vents you sealed. Looks like you may already suspect this by this line in your original post "Perhaps the HVAC room is blasting cold air out of it into the garage (the door to it has at least 1" between it and the floor)." This should be easy enough to check just by closing the door and feel at the bottom of the door with your hand or use one of the many other simple tests like smoke, candle, flame, etc.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by sperry8 »

snackdog wrote: Sun Jun 02, 2024 8:48 pm Our basement is chilly as well. We put a fan at the base of the stairs and attach a smart plug in July-Sept. If it gets over 80F outside, the fan comes on an blows cold air into the kitchen during the afternoon. Works ok.

We also have a damper for half the basement, but leave it half open. HVAC guy said not a good idea to close it completely and have no air to the basement. You need some circulation down there.
I have one damper open (but the rest closed). I also keep the basement door ajar at all times so air is able to flow through. I do understand this may not be enough. Tbh, it really doesn't matter if the dampers are open or closed - temps are 64 and below either way. So perhaps I should just open another one or two.
Gearheaddd wrote: Sun Jun 02, 2024 8:58 pm You want to try and pull the air out of the basement and mix it with the air circulating throughout the house. If done correctly it should dehumidify the basement air and even save money on a/c since you’ll be introducing more cold air into the mix.

You should be able to add a large, adjustable register to the furnace return plenum that, when open, will pull in basement air, run it over the evaporator coils to dehumidify it and send it throughout the upper living area.

https://www.homedepot.com/p/TruAire-18- ... /203313490

You may need to experiment a bit with closing off basement registers and possibly add a dehumidifier to the basement if it’s too damp ( a dehumidifier will also help raise the basement temperature a bit). Initially leave the door to the basement open to see if you need to add a simple register or two in the floor between the upper living space and basement to allow better circulation. Finally, you need a thermostat which allows you to set your blower on “circulate” which will cause the air to move throughout the basement and upper living area for 30% or so throughout the day regardless of whether the system is calling for cooling.

I live in the northeast and have a similar setup which works very well using this method.
So that was my original question... should I add a return downstairs? If I understand this "add a large, adjustable register to the furnace return plenum that, when open, will pull in basement air, run it over the evaporator coils to dehumidify it and send it throughout the upper living area." correctly, a return that pulls air from the basement, goes through the AC and then the AC can push it back out does what you're suggesting, yes?

I always leave the basement door to upstairs ajar (1/2 way) so air can go to from (w/o a return downstairs you can feel air under the door if not). Regardless temps don't change either way.
z0r wrote: Mon Jun 03, 2024 1:43 am adding a basement return should help yes. it should be greater than or equal to the basement supply registers. if you don't have basement supply registers and your goal is to have it fully conditioned, add those also

once you have the basement return then you can set your thermostat to run in fan only mode on some schedule to get air mixing and average out the house. if you're lucky enough to have a multi speed air handler (didn't check your part #) some people will even run at the lowest speed 24/7 . 4 tons is a lot, yeah you had a manual j, but it's still a lot for just AC. is it a heat pump - maybe it was sized for heating? in the northeast a heat pump would normally be sized for heating and could be 2x bigger than it needs to be for cooling so you won't get much air mixing in the summer without a way to run fan only

a more extreme measure is to install a dedicated "anti stack" duct to take air from the highest practical point in the house and blow it to the lowest point (separate from your regular ductwork), plus some kind of return transfer grille. you can run this with an efficient fan 24/7 so it could only take a few tens of watts. it would be like a supercharged version of running the overall system as fan only, it can counteract your stratification directly
I do not know if it is a heat pump but I highly doubt it. I'd love the stack idea but I'd have to rip apart walls and floors to do it. Maybe I can figure out a way to do this without tearing apart too much.
j.click wrote: Mon Jun 03, 2024 5:54 am HVAC Pro informed me that an easy partial mitigation is to keep blower fan 'on' all the time and not cycle. Less stress on motor than on/off cycles and helps distribute overall house air better. Hope this helps....
Jack FFR1846 wrote: Mon Jun 03, 2024 6:40 am Our home is basement with 7' ceilings, but all open, nothing finished, no sheet rock except over the furnace. First floor is normal. 2nd floor cathedral ceilings where roof is cape with dormer for the entire south side. I can equalize the entire house simply by switching the fan from run with the AC to on. This circulates air through the system from both floors. Our ducts are big enough and insulated so while the basement stays cool, I'd say it's maybe 3-5 degrees colder than the first floor. We have no ducts at all in the basement.

So in short, turn the fan switch to "ON".
firebirdparts wrote: Mon Jun 03, 2024 6:44 am The earth is about 50 degrees, so your best bet is to take advantage of that by moving more air. Make sure air is getting upstairs from the basement whether you put a return in or not, and then leave the fan on all the time. You could put a return in the basement but really you need the opposite. You need to pump air from up to down without cooling it.
A bunch of folks are suggesting running the fan. Nest seems to allow 8 hours of fan "on" only. I will have to see if there is an override to make it 24/7.
galving wrote: Mon Jun 03, 2024 6:57 am Your basement is isolated by the spray foam, and more recently by blocking the vents.
This prevents you from controlling the temperature and humidity. This is visible on the temp data you provided.

You can check for duct leaks, though it's unlikely that this would resolve your issue because you don't have a system that's capable of controlling both the upper floor and the basement independently.

There is no circulation from the upper floors to the lower floors. This prevents the 'system' from being well mixed.
It's likely better to set up a different unit for downstairs.

Good luck,
galving
The temperature I sent was shown before I blocked the vents. The blocking of vents doesn't increase the isolation (which still may be true and likely is) but it's not the vents per se. I also keep the basement door open to reduce the isolation but apparently that doesn't help. Perhaps the return pulls air whereas the door open does nada.

Setting up a 2nd system is what Im trying to avoid - it will cost tens of thousands and require me ripping apart walls, ceilings, etc. Thus me trying to find every other option prior. Reality is - the 2nd system is just going to be heat on if we can't find a solution - so a mini split would do the trick (imo) and at least not require a full 2nd system.
Target2019 wrote: Mon Jun 03, 2024 7:26 am Your basement is an insulated cooler. However, there are probably a significant number of ways for A/C air to fall into the basement cooler. Your garage is affected in a similar way.

A return vent, sized properly, will restore some balance in the temperatures, floor to floor.

You also can find the routes through which cold air gets into the basement space, and remediate those. Maybe a temperature gun would help.

In our home we have two floors and a basement. There are two (2) HVAC systems, one for each floor. The basement has no vents or returns. There is one door to the basement. If I leave that door ajar, I can easily lower the temperature of the basement. When A/C is in use, though, it will run longer on both of the higher floors when that door is open.

What helped me to understand the complex situation was, think of your home as a box that is filling with cold air. If the floors are not isolated from each other, your systems are running to fill that space, and then the cooled or heated air can trigger your thermostat(s) to pause the HVAC.
I took a temperature gun to the whole basement... found no sig differences anywhere except the floor. You do bring up an interesting point about my basement door. I had been leaving it open... but maybe I should leave it closed. At least then the AC will run less for the main floor (possibly).
mpnret wrote: Mon Jun 03, 2024 8:45 am You sure that the basement installed HVAC unit isn't blasting cold air into the downstairs space from somewhere else other than the supply vents you sealed. Looks like you may already suspect this by this line in your original post "Perhaps the HVAC room is blasting cold air out of it into the garage (the door to it has at least 1" between it and the floor)." This should be easy enough to check just by closing the door and feel at the bottom of the door with your hand or use one of the many other simple tests like smoke, candle, flame, etc.
I'm not sure - but can't find any cold air leakage (except for a tiny amount right from a little hole in the insulation in the HVAC room. I just feel that the garage shouldn't be so cold as well - so something could be up. I'd say however, it could be that ground is 50 degrees and even though the garage has one side open - it is 2 sides to the 50 degree ground and as such, cold.

So after all the comments I see 3 possible answers (prior to mini split or continued use of summer space heaters):

1- Blow fan 24/7. If Nest allows it - I will do it. If not I may remove the Nest and install one that does allow it.
2- Add a return to the basement. Quote was $1k. Figure it can't hurt but has a chance to help.
3- If 1 & 2 make no difference, see if there is any reasonable method to blow air from top of cathedral into basement without tearing house apart. It is possible I could do this through the attic and down through a linen closet. Q: Would it help if I blew that air from basement to top of cathedral? Or does it have to be top pushing down.

Appreciate all the responses... always open to more if anything pops up or someone new reads the thread.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by bombcar »

sperry8 wrote: Mon Jun 03, 2024 4:20 pmQ: Would it help if I blew that air from basement to top of cathedral? Or does it have to be top pushing down.
Air has to circulate, if you blow from the basement up, where does the replacement air come from? If it backdrafts furnace/water heater that could be bad, if you replace the basement door with one with louvers it might be fine.

You could try turning the entire system off for a few days/week if possible, and see what the "natural" temperature of the basement is. If there's enough dirt around it, it might be 50-60 degrees without any cooling whatsoever.

And if that's the case, you need more heat down there somehow.
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walkabout
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by walkabout »

Where in the northeast is your home? Southern Massachusetts? Northern Maine? That will help readers understand the climate that your home was designed for.

Was the idea of a finished basement included in the original design? Were the uses of the basement considered? This question could probably also be read as Was your home designed (including HVAC) such that the upstairs is really the main living level and the basement might be used only occasionally?

Is your HVAC designed to heat/cool the whole home? Or is it designed just for the upstairs. You state that there are vents downstairs, so I assume the HVAC capacity is appropriate for the whole home. I will say that, generally, people have a lot of problems heating/cooling a two story home evenly with only one HVAC system (or a non-zoned system).

Did you have the home designed and built? Or did you buy it “off the rack”?

Have you contacted the builder?

From your posts, it sounds like you have ended up with two significantly different climates in your home. Getting more circulation between the upstairs and the basement will probably help, but (during cooling season) you would be mixing cool air from upstairs with colder from downstairs. This might moderate the downstairs temp somewhat, but you might also be “overcooling” the upstairs (with the cold moist basement air), which might leave the upstairs a little muggy (since the AC might not run as much as it would otherwise). A dehumidifier downstairs might help. It will reduce humidity and raise the temperature somewhat.

What about in the winter? What kind of problems will you have then? Basement still too cold, but at least running the heat is normal vs the counterintuitive idea of running the heat during the summer. Whatever solution you come up with now may or may not help with any winter problems.

This problem probably needs a holistic solution. You might consider:
1. Talk to builder or HVAC contractor to see if there is a logical explanation for the problem (seems like it should have been accounted for in the design).
2. Implement temporary solutions to get through the summer: fans, dehumidifier, leave the door open more.
3. Live with the issue in the winter to get an idea of what problems will crop up in cold weather.
4. Next spring implement something more permanent that, empirically, has a good chance of helping.

Depending on your experience, you might find the problem is summer only (too cold in basement in summer, but ok in winter), summer and winter, or some combination.

Some solutions could be:
1. Better air circulation, dehumidifier, possibly auxiliary heat source (eg oil filled radiator).
2. Second HVAC system, such as a mini split.

Good luck!
The Stone Wall
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by The Stone Wall »

Please do a google search for "average soil temperature" for your location. I did a few locations in the Northeast and found values around 60 degrees. That doesn't seem to different from the values you found for the garage and basement. Evidently, your garage doors have decent R values. The air in the garage has a higher dew point/humidity because it is not being conditioned from your system. However, your primary problem is that the area underground is functionally the same temperature as the average ground temperature.

Your home doesn't allow any way to warm the basement space naturally. The temperature coming out of the basement vents would be an indication if they are adding significant cooling to the space when the AC is on. I am not a believer in closing vents because it simply adds pressure against the HVAC fan. A return should have been installed in the basement during construction. It's a lot of space without a return. A return might be more beneficial during the winter during heating mode. A return will add some mixing of the air.

I'm curious about the idea of piping 1st floor air directly down to the basement. An analysis would be needed to determine what the effect of mixing the two air volumes would be. Moving warm air to a cooler space would increase the humidity. Anything above 55-60% humidity starts to cause musty conditions. How many air exchanges would be necessary to overcome the cooling effect of the walls/floor?

The bottom line (with your home design and location) is that you will have to heat the air in the basement if you want it to be warmer than the soil temperature during the summer. Is it the space comfortable during the winter?
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by JeffAL »

I have a similiar sized, much older house with basement way farther south and my hvac unit is 2.5 tons. Maybe your hvac is oversized.
z0r
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by z0r »

sperry8 wrote: Mon Jun 03, 2024 4:20 pm A bunch of folks are suggesting running the fan. Nest seems to allow 8 hours of fan "on" only. I will have to see if there is an override to make it 24/7.
one note on running the fan... a 4 ton system can draw as much as 750 watts for the air handler, depending on air handler quality, duct resistance and speed settings. that could be counterproductive to run 24/7 if it's that much, it would heat your house up and cost a lot. if you can run at lower speed, you're lucky with duct resistance, etc. it could be only 100-300 watts and more reasonable to run all the time, so maybe measure the current and see. it's common to run something like 10 minutes/hour, my ecobee thermostat allows that type of programming
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by toomanysidehustles »

We have a walk-out basement (in Colorado=cold) and after having 3 years in a row of freezing pipes, we added a Jotul gas fireplace on its own thermostat. I set it to 60 and no issues since. 20 minutes before we want to watch a movie, we crank it up to 70. Low 7' ceiling height warms it up pretty quick. Same might work for you if it's like a meatlocker in the summer....though my kids would love it being so cool in the summer!
The Stone Wall
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by The Stone Wall »

I thought a little more on this overnight. The temperature coming out of the vents is around 55 degrees depending on the AC efficiency. All of the temperature readings you posted were taken in the morning, which may have caused the close similarity between garage and basement temperature readings. Are they that similar around 2 in the afternoon on a warm sunny day?

There is a way to check if moving warm air from the 1st floor to the basement will work. Open the basement door and close off some/most of the first floor vents. (the door has to be open to allow air exchange) Turn off the AC and place the unit in "fan on" only mode. This should essentially move all 1st floor air into the basement via the HVAC fan. Monitor and plot basement temperature with time. I would start with 15 minute intervals but I doubt if the temperature increase will be that rapid. I believe you also said you can measure wall temperatures. Record and plot those data as well. This should tell you how much the basement wall surfaces are controlling the temperatures of the space and whether or not moving air will make a difference.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by mpnret »

The Stone Wall wrote: Tue Jun 04, 2024 9:05 am I thought a little more on this overnight. The temperature coming out of the vents is around 55 degrees depending on the AC efficiency. All of the temperature readings you posted were taken in the morning, which may have caused the close similarity between garage and basement temperature readings. Are they that similar around 2 in the afternoon on a warm sunny day?

There is a way to check if moving warm air from the 1st floor to the basement will work. Open the basement door and close off some/most of the first floor vents. (the door has to be open to allow air exchange) Turn off the AC and place the unit in "fan on" only mode. This should essentially move all 1st floor air into the basement via the HVAC fan. Monitor and plot basement temperature with time. I would start with 15 minute intervals but I doubt if the temperature increase will be that rapid. I believe you also said you can measure wall temperatures. Record and plot those data as well. This should tell you how much the basement wall surfaces are controlling the temperatures of the space and whether or not moving air will make a difference.
What would cause the 1st floor warm air to drop down to the cooler basement? Only return is on the 1st floor.
The Stone Wall
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by The Stone Wall »

mpnret wrote: Tue Jun 04, 2024 10:05 am
The Stone Wall wrote: Tue Jun 04, 2024 9:05 am I thought a little more on this overnight. The temperature coming out of the vents is around 55 degrees depending on the AC efficiency. All of the temperature readings you posted were taken in the morning, which may have caused the close similarity between garage and basement temperature readings. Are they that similar around 2 in the afternoon on a warm sunny day?

There is a way to check if moving warm air from the 1st floor to the basement will work. Open the basement door and close off some/most of the first floor vents. (the door has to be open to allow air exchange) Turn off the AC and place the unit in "fan on" only mode. This should essentially move all 1st floor air into the basement via the HVAC fan. Monitor and plot basement temperature with time. I would start with 15 minute intervals but I doubt if the temperature increase will be that rapid. I believe you also said you can measure wall temperatures. Record and plot those data as well. This should tell you how much the basement wall surfaces are controlling the temperatures of the space and whether or not moving air will make a difference.
What would cause the 1st floor warm air to drop down to the cooler basement? Only return is on the 1st floor.
The HVAC fan would take the air entering the return in the 1st floor and discharge it out the basement vents. The process would have to cycle the air. This all has to happen in fan only mode with no AC.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by corduroysuit »

sperry8 wrote: Sun Jun 02, 2024 7:59 pm
Looking for some HVAC advice.
Do you happen to have a heat pump water heater installed in the basement? If so, it will make the basement noticeably cooler. I'd be surprised if it accounted for the full 10°F of difference, but it seems worth a mention.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by Amien »

Ditto re need for adequate-sized dehumidifier in basement, at least here in Great Lakes Midwest. We installed supplemental electric baseboard along one wall of habitable basement room, which also has gas fireplace. Voila! Comfortable guest room / office-library for all seasons.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by tm3 »

Hopefully there is a less expensive solution, but, once I installed a whole house dehumidifier everyone became comfortable with the thermostat set to 78, which gives a basement temp of about 72. Plus no more mold.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by SpaghettiLegs »

You can consider using a smart thermostat with remote sensors. Ecobee is what I have, although I don’t use the sensors. You could put a sensor in the basement and then work out a comfortable average between your zones.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by sperry8 »

z0r wrote: Mon Jun 03, 2024 11:12 pm
sperry8 wrote: Mon Jun 03, 2024 4:20 pm A bunch of folks are suggesting running the fan. Nest seems to allow 8 hours of fan "on" only. I will have to see if there is an override to make it 24/7.
one note on running the fan... a 4 ton system can draw as much as 750 watts for the air handler, depending on air handler quality, duct resistance and speed settings. that could be counterproductive to run 24/7 if it's that much, it would heat your house up and cost a lot. if you can run at lower speed, you're lucky with duct resistance, etc. it could be only 100-300 watts and more reasonable to run all the time, so maybe measure the current and see. it's common to run something like 10 minutes/hour, my ecobee thermostat allows that type of programming
I took at look at the manual for my system and it pulls ~198 watts for fan only (only single speed fan so it is what it is). I do wonder what extra it will cost to run fan 24/7 but this is currently what I'm doing (see below for more details).
The Stone Wall wrote: Tue Jun 04, 2024 9:05 am I thought a little more on this overnight. The temperature coming out of the vents is around 55 degrees depending on the AC efficiency. All of the temperature readings you posted were taken in the morning, which may have caused the close similarity between garage and basement temperature readings. Are they that similar around 2 in the afternoon on a warm sunny day?

There is a way to check if moving warm air from the 1st floor to the basement will work. Open the basement door and close off some/most of the first floor vents. (the door has to be open to allow air exchange) Turn off the AC and place the unit in "fan on" only mode. This should essentially move all 1st floor air into the basement via the HVAC fan. Monitor and plot basement temperature with time. I would start with 15 minute intervals but I doubt if the temperature increase will be that rapid. I believe you also said you can measure wall temperatures. Record and plot those data as well. This should tell you how much the basement wall surfaces are controlling the temperatures of the space and whether or not moving air will make a difference.
Thank you for giving this so much thought, I truly appreciate it! It is a good idea and one which I may do if my current experiment which is helping doesn't continue to work.
JeffAL wrote: Mon Jun 03, 2024 8:49 pm I have a similiar sized, much older house with basement way farther south and my hvac unit is 2.5 tons. Maybe your hvac is oversized.
My HVAC is most likely oversized. Perhaps someday when it breaks I'll install a smaller unit. As it's brand new now guess I'll just have to live with it.
Amien wrote: Tue Jun 04, 2024 5:34 pm Ditto re need for adequate-sized dehumidifier in basement, at least here in Great Lakes Midwest. We installed supplemental electric baseboard along one wall of habitable basement room, which also has gas fireplace. Voila! Comfortable guest room / office-library for all seasons.
tm3 wrote: Wed Jun 05, 2024 6:30 am Hopefully there is a less expensive solution, but, once I installed a whole house dehumidifier everyone became comfortable with the thermostat set to 78, which gives a basement temp of about 72. Plus no more mold.
I have a dehumidifier on both floors. Frigidaire 50-Pint Portable Dehumidifier on the main floor and it's slightly smaller cousin in the basement. Both work great.

So on to where I'm at:

Based on this threads suggestions I have decided to run the AC fan 24/7. I have been doing this for ~48 hours now and it has made quite a difference. The delta between floors is now 4° rather than 8-10° degrees previously. A huge difference in usability.

You can see the new temperatures here: https://ibb.co/x65L3Kg (note humidity is a bit higher because it's raining out).
(for quick reference here were the old temps, pre- 24/7 fan: https://ibb.co/CQNVYCq)

It appears the humidity levels in my basement (not upper floor) jumped once I turned the fan on 24/7. No problem though, as I have 2 portable dehumidifiers that I can use. So I turned on the smaller 35 pint one in the basement and that keeps the humidity at 55 quite easily (and spits out a tiny bit of heat as well). I say tiny, because I ran it last year (pre-fan) and it didn't dent the icebox that was my basement. So on it's own it doesn't generate enough heat to matter. But now with the fan on 24/7, i'll take the marginal heat it generates.

The humidity in the basement is slightly higher on the last screenshot because the humidifier filled up overnight so it stopped running. I may swap the 50 pint down there which runs for much longer before needing to be emptied. Either way, managing a dehumidifier is fine for me. It was the temps that were an issue.

Since the fan is now somewhat mitigating this issue and balancing the house slightly better, it appears the theories that posited what I have is a basement cooler (all tightly covered without any way for air to get in/out) were correct. So now this brings up the next questions:

1- Would it still help to add a return down in the basement? (now that we know the fan is helping, does this give us a clue re whether a return would help?)
2- Would it still help to add a run pushing air from the cathedral (top) to the basement? Or is this overkill now that the 24/7 fan appears to be working
I'm asking the above 2 questions, because I have yet to see the cost of running the fan 24/7. The manual said 198 watts and at my KW cost for delivery and electricity of ~$.2 cents per KW - that appears to be in the neighborhood of ~$30 per mo (in the summer). If so, that's fine (although I do wonder if that'll burn out my AC unit faster). Thus perhaps I should still add 1 or 2 above (if they'll help).

Two other things to mention:
1) I realize I could add a whole house dehumidifier however, my HVAC room is very tight and it would be difficult to fit (I had 2 contractors out to quote an install). It can be done, but I may have to take space from the adjacent room (which means ripping out walls and expanding the HVAC room). Thus, I have the portables and can use them until I decide what to do.
2) this is a summer vacation home - so I don't care about the winter(s). I keep temps at 50° and the basement stays at 52° and the main floor at 50° (both are fine) as are winter humidity levels (all this happens w/o fan on).

Thank you to all for your suggestions. Even 2 HVAC repairmen never suggested running fan 24/7. They suggested 2 mini splits in the basement heating it all summer. Bogleheads to the rescue again!
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oldlongbeard
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by oldlongbeard »

These are very inefficient strategies. The only TRUE issue you have is the main room with cathedral ceiling on main level is too WARM. THAT is where you install a mini split. Adjust your main HVAC T-stat to make basement comfortable. Adjust mini split to make large living area comfortable. High ceilings are great, but insulating them against sun heated roof is near impossible at times. The mini split so installed will allow you to make this largest living area comfortable year round.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by tm3 »

sperry8 wrote: Thu Jun 06, 2024 7:26 am
I have a dehumidifier on both floors. Frigidaire 50-Pint Portable Dehumidifier on the main floor and it's slightly smaller cousin in the basement. Both work great.
Again, just as an FYI as I don't know your optimum solution, but I was running a couple of 50 or so pint dehumidifiers before installing the whole house unit. I was amazed at how much more effective the whole house unit is, and I was more amazed at how much less electricity it uses.
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by firebirdparts »

I think a return in the basement is a problem. What happened before is that you pumped refrigerated air into the basement and there was nothing going on down there to heat it up. The air came in at 50F, and the ground is 50F. So, if you put a return down there, you would potentially rob from the return upstairs or maybe even close that up. I see this as doing absolutely nothing to help you.
This time is the same
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by z0r »

sperry8 wrote: Thu Jun 06, 2024 7:26 am 1- Would it still help to add a return down in the basement? (now that we know the fan is helping, does this give us a clue re whether a return would help?)
2- Would it still help to add a run pushing air from the cathedral (top) to the basement? Or is this overkill now that the 24/7 fan appears to be working
I'm asking the above 2 questions, because I have yet to see the cost of running the fan 24/7. The manual said 198 watts and at my KW cost for delivery and electricity of ~$.2 cents per KW - that appears to be in the neighborhood of ~$30 per mo (in the summer). If so, that's fine (although I do wonder if that'll burn out my AC unit faster). Thus perhaps I should still add 1 or 2 above (if they'll help).

Two other things to mention:
1) I realize I could add a whole house dehumidifier however, my HVAC room is very tight and it would be difficult to fit (I had 2 contractors out to quote an install). It can be done, but I may have to take space from the adjacent room (which means ripping out walls and expanding the HVAC room). Thus, I have the portables and can use them until I decide what to do.
2) this is a summer vacation home - so I don't care about the winter(s). I keep temps at 50° and the basement stays at 52° and the main floor at 50° (both are fine) as are winter humidity levels (all this happens w/o fan on).

Thank you to all for your suggestions. Even 2 HVAC repairmen never suggested running fan 24/7. They suggested 2 mini splits in the basement heating it all summer. Bogleheads to the rescue again!
if you're able to keep the house at a temp you want with fan operation, cooling the upstairs using the basement's natural cold temp (and bringing the downstairs up in temp as well), that could be EXTREMELY efficient and a good use of 200 watts. I grew up in a house that didn't need AC at all because it was designed to do this. this is offset by the power draw of the dehumidifiers but you can quantify that and see

as for burning out your blower motor, yes it might have a reduced life but they're relatively cheap and easy to swap

I still think a basement return is a good idea if pursuing this air mixing strategy
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by sperry8 »

z0r wrote: Thu Jun 06, 2024 11:40 am
sperry8 wrote: Thu Jun 06, 2024 7:26 am 1- Would it still help to add a return down in the basement? (now that we know the fan is helping, does this give us a clue re whether a return would help?)
2- Would it still help to add a run pushing air from the cathedral (top) to the basement? Or is this overkill now that the 24/7 fan appears to be working
I'm asking the above 2 questions, because I have yet to see the cost of running the fan 24/7. The manual said 198 watts and at my KW cost for delivery and electricity of ~$.2 cents per KW - that appears to be in the neighborhood of ~$30 per mo (in the summer). If so, that's fine (although I do wonder if that'll burn out my AC unit faster). Thus perhaps I should still add 1 or 2 above (if they'll help).

Two other things to mention:
1) I realize I could add a whole house dehumidifier however, my HVAC room is very tight and it would be difficult to fit (I had 2 contractors out to quote an install). It can be done, but I may have to take space from the adjacent room (which means ripping out walls and expanding the HVAC room). Thus, I have the portables and can use them until I decide what to do.
2) this is a summer vacation home - so I don't care about the winter(s). I keep temps at 50° and the basement stays at 52° and the main floor at 50° (both are fine) as are winter humidity levels (all this happens w/o fan on).

Thank you to all for your suggestions. Even 2 HVAC repairmen never suggested running fan 24/7. They suggested 2 mini splits in the basement heating it all summer. Bogleheads to the rescue again!
if you're able to keep the house at a temp you want with fan operation, cooling the upstairs using the basement's natural cold temp (and bringing the downstairs up in temp as well), that could be EXTREMELY efficient and a good use of 200 watts. I grew up in a house that didn't need AC at all because it was designed to do this. this is offset by the power draw of the dehumidifiers but you can quantify that and see

as for burning out your blower motor, yes it might have a reduced life but they're relatively cheap and easy to swap

I still think a basement return is a good idea if pursuing this air mixing strategy
Thanks for your thoughts. After another 24 hours I am now at a 2° delta between my basement and main floor (previously it was 8-10°). So the 24/7 fan and portable humidifier are working. Amazing!!

And you are correct - the fan always running means we are using A/C less as the main floor feels slightly cooler than before. Not sure this will hold up in Jul/Aug - but it is the case in Jun.

I will wait 30 days to see the price of running these items 24/7 and then decide if I want to install the return. Some (like you) feel it'll help - others (right above you) feel it won't. So I'm hesitant to do it at the moment. Of course, I can always close it up if it doesn't work. I'd like to get a sense of the cost of my current setup vs the 1x cost of adding the return. Currently estimate it'll be a 4 yr breakeven (but i'll know more in 30 days).
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Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by StrongMBS »

A couple of questions about your house.
Do you have a picture of the basement after the ductwork was done but before the basement was finished?

What is the construction of the wall between the finished basement and the HVAC room and garage area and how is it insulated, and the doors sealed?

What is the construction of the wall between the HVAC room and garage area and how is it insulated, and the doors sealed? (I believe this is not good since there's an inch gap at the bottom)

Is the HVAC system in a semi-finished area (i.e., are the floor and wall to underground sealed with closed foam like the finished basement)? Or like the garage?

Most of this is a physics problem that is easy to understand if you have the right model so first let’s start with some general high level HVAC concepts.

Manual J report (load calculation) although a start it only sizes the equipment for heating and cooling the building. An important aspect of this is determining the contributing humidity factors in the house (cooking, bathing, house envelope tightness) which has a large impact on the needed size of the AC unit.

For a properly designed HVAC system a Manual D (Ductwork Sizing) is also needed. For uniform comfort each closed area (i.e., room) needs a return or a low resistance path for the air to find its way to an air return.

Do you have a Manual D?

Unless the ductwork has mechanism to be reconfigured between heating and cooling (most are not) any ductwork is a compromise between the needed airflow for a room in the heating and cooling state (which can be significant - especially with south facing rooms and basements).

A blower door test determines a home’s airtightness does not directly test your air duct leakage.

If your HVAC system is in an unfinished area the air leakage of the ductwork in the that area is very important especially for the return while using AC if the unfinished area has high humidity. This problem is usually compounded if the air return is undersized or has high air resistance causing more air being sucked from the unconditioned area.

Both AC units and a dehumidifier work under the same principle, except the heat generated from the dehumidifier is placed back into the area – not a great setup if you are also trying to cool the area.

If you are using AC in a properly sealed living area, you should not need to run a dehumidifier unless there is air leakage into the system somehow or the AC system is not properly designed (mostly oversized since that causes short cycling which will not allow for the humidity to be removed).

Cold air sinks, warm air rises.

In the Northeast, unfinished underground basements are cold (50-60F) and humid because the ground below the floor and much of the walls are that temperature and moist. Concrete lets the water vapor pass easily and provides little insulation.

For a first a first order approximation let’s think of your garage as an unfinished basement (assume your doors are tight and the doors are not facing the south sun). It will be cold and humid even without outside humid air coming in.

I assume your utility room is the same, yes?

Let’s assume that your basement is sealed and insulated properly from these areas: floor, ground walls, ceiling, garage, HVAC room, and door to rest of the house.

If there were no external forces to the basement (i.e., no AC/Heat or doors open) steady state it would be my guess around 55-65F depending on the relative insulation values in the ceiling and walls/floor. This would be a fight of the 50F ground against the insulation of the floor and walls versus the 74F upstairs against the ceiling insulation.

So yes, this is normal, acceptable no but normal yes. Unless something is done to combat the issue.

BTW in winter you will be happy that you have some air from the HVAC system, but it does not need much compared to the rest of the house (50F ground vs 20F air) to keep a properly insulated finish basement warm.

Open the door and turn on the AC just on the first floor (with no air flow to the basement) air only moves down to the basement if it colder than the air already there or the air return vents are undersized and the return is sucking air from the basement.

Now if you turn on the AC and it has airflow into the basement but no air return in the basement the air must go somewhere. Either the warmest air of the basement gets pushed up the stairs into the 1st floor or the duct returns have leaks and the warmest air of the basement air (the air next to the ceiling) gets sucked into the return duct. Either way the basement gets colder if the air from the AC is colder than the starting air temperature of the basement.
If I remember right the normal AC temperature drop is around 15-20F so for 75F this would be 55-60F air.

Running just the HVAC system fan with air flow in the basement helps circulate the 74F upstairs air into the colder basement. My bet is that if the basement had an air return, then while running the fan alone would warm the basement faster since the colder basement air would be mixed with the warmer upstairs air.

I assume your HVAC room is unconditioned and like your garage and is cool and humid like an unfinished basement.
If you run with just the HVAC system fan only and you have increased humidity problem most likely the air is being sucked into the system from your HVAC room since it is an unconditioned area. This is most often caused by poorly sealed duct in the unconditioned area (an easy thing to fix) and undersized return vents, duct, and filters (which most houses have), often an expensive thing to fix with a finished basement.
But adding a return from the basement and maybe living with a draft down the stairs (keep the door open or cut it short or add an air bypass into the door or wall next to it) might be a compromise.

Also it might be advantageous while just running the HVAC fan alone the return in the basement would be oversized (using an electric damper) to encourage more than normal air being suck from the basement at the expense of a draft down the stairs with the door open.

But without running a Manual D it is very hard to tune a system.

The first thing I would do is seal any duct work and seams on the HVAC equipment in the HVAC room. Especially around where the filter is inserted if at that location. Note remove the insulation and seal the seams, then replace the insulation – use approved UL tape or mastic.

Then add a return to the basement then try to tune the system which will be different in the winter. But first make sure the door between the basement and the garage is well sealed, you do not to pull humid air into the system.

A word of caution depending on the heating system exhaust requirements sealing the HVAC room from the garage might not be good idea. BTW where is your water heater? It also may have exhaust requirements.
StrongMBS
Posts: 73
Joined: Sat Jan 14, 2017 1:38 pm

Re: Basement is freezing due to HVAC - thoughts/fixes?

Post by StrongMBS »

Basements in the NE have 3 problems heat loss/temperature, humidity, and radon often needing nonstandard solutions to HVAC and water distribution problems.

Over the weekend I was curious to see if my Manuel J software would generate a negative sensible heat gain (temperature) for your basement, unfortunately my license had expired so I couldn't play around with it. Here are the things I have learned trying to solve this issue for my house and others.

Again, although not intuitively obvious unless you analyze it or have experience with solving this problem, even your finish basement (most likely) has heat loss 365 days a year given your desired temperature setpoint (74F). I do not have this issue since my finish walkout basement area is my workout area which I like cool so the year-round steady state temperature of 55-65F is ideal for me.
Given the temperature and humidity readings your garage looks like an unfinished walkout basement. A word of caution that high dewpoint (57F) could cause issues, condensation on any water equipment and pipes if in that environment if not properly insulated leading to mold since often the incoming well or town water is below that temperature (50-60F) just like the ground.

Hopefully the humidity in your finished basement is caused by using the door to the garage (this assumes the finished basement was sealed properly). So, unless you are going to dehumidify your garage (seems like an expensive solution if you use your garage doors in the summer), every time you open up the door to your finished basement the cool moisture from the garage rushes in.

Normally in an AC environment this latent heat gain (moisture/humidity) is removed in the normal AC process. But since there is no sensible heat gain (temperature), in fact it is negative, in the finished basement there will not be enough air flow exchange to dehumidify the basement area even if you had a return in a balance system. You might be able to unbalance the system (i.e., have an oversize return in the basement) tuning the system would be very complicated and mostly through trial and error.

The easiest and most energy efficient solution is a portable dehumidifier in the basement (which I think you already have). If this is your long-term solution, for convenience I would suggest using a setup with direct drain connection, so you do not have to empty the water bucket all the time.
Somewhere in the HVAC room is either a drain or a pump to remove the condensation from the AC equipment. Place the dehumidifier on a platform (so the water will flow down the hose/pipe) and pass a connection into the HVAC room through the wall to that setup. Caution about using this setup in wintertime if the HVAC room gets below freezing, although you shouldn't need the dehumidifier in the winter. Put the dehumidifier in a pan and add a water alarm in case something goes wrong.

Most HVAC guys will not offer running the fan 24/7 as a solution to anything since they don't want to take this service call when the fan fails.

Your current solution of running the HVAC system fan 24/7 is very inefficient for several reasons. First, with no return and the small duct size in the basement little air flow (compared to the air being moved by the fan) is being exchanged with the basement and the rest of the house.

Here are some more efficient solutions I have seen work.

One is a large direct vent from upstairs to the basement with a separate small fan that runs when the AC is not. This unfortunately usually allows too much noise between the basement and the first floor to be acceptable for many situations. Although adding turns and using soundproofing inside the duct might make an acceptable solution. Depending on the amount of air you need even a small bathroom a fan might work. This could be placed on a timer to only run during the day.

Another solution is if you have access to the returns in the HVAC room is the place a bypass with a fan and electronic damper (normally closed) between the return to a new vent into the basement. Run the fan when the AC is not on, and the temperature is not warm enough for your comfort. Sorry I could not find the webpage that had a great explanation on this setup that I thought I had saved.
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