Third floor too hot with central A/C: options?

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coalcracker
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Third floor too hot with central A/C: options?

Post by coalcracker » Fri Feb 23, 2018 2:12 pm

I am in the midst of a significant remodel of a newly purchased home. It has central heat and A/C, and a finished attic in which we are 2 large bedrooms, a landing, storage closet, and full bath.

We have noticed this winter that the central heat works well on the third floor, but were warned by the previous owner (as evidenced by a window A/C unit on the third floor) that the central A/C does not work well in the summer heat. We are in PA to give you an idea of the climate.

It seems like overkill to add another HVAC unit for a single floor. I have been reading about ductless Mini Split A/C systems, but they get pricey particularly with dual zone systems, which we would need with the layout of the floor. Because of some changes we are making to the layout of this floor, the current single window unit will not work well.

Any other ideas for improving cooling on this floor in the summer?

bloom2708
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Re: Third floor too hot with central A/C: options?

Post by bloom2708 » Fri Feb 23, 2018 2:16 pm

What do you do with your vents in summer in winter?

In summer, we close all basement vents. I partially close some main floor vents. All vents open on the 3rd/top level.

In winter, we reverse. All basement vents open. Main floor vents about the same, maybe a bit more open. All vents on top floor fully closed.

We run the "fan only" 50 minutes of every hour. That helps to keep mixing air.

Cold air sinks and hot air rises. There is no fixing that. Adding a second AC unit and using that for the top floor vents (closing off and making a second zone) would be your next step. Add a thermostat upstairs. Keep it set to keep the 3rd floor comfortable. Cold air will continue to sink to lower levels, but that could keep the lower level AC unit from running at times.
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lthenderson
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Re: Third floor too hot with central A/C: options?

Post by lthenderson » Fri Feb 23, 2018 2:22 pm

coalcracker wrote:
Fri Feb 23, 2018 2:12 pm
Any other ideas for improving cooling on this floor in the summer?
There are now a number of companies that make smart vent covers that essentially turn every room into its own zone. They replace your old vent covers and after you program them with your smart phone, open and close to maintain your desired temperature in every room. I don't have any so I can't vouch how well they work.

coalcracker
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Re: Third floor too hot with central A/C: options?

Post by coalcracker » Fri Feb 23, 2018 2:26 pm

bloom2708 wrote:
Fri Feb 23, 2018 2:16 pm
What do you do with your vents in summer in winter?

In summer, we close all basement vents. I partially close some main floor vents. All vents open on the 3rd/top level.

In winter, we reverse. All basement vents open. Main floor vents about the same, maybe a bit more open. All vents on top floor fully closed.

We run the "fan only" 50 minutes of every hour. That helps to keep mixing air.

Cold air sinks and hot air rises. There is no fixing that. Adding a second AC unit and using that for the top floor vents (closing off and making a second zone) would be your next step. Add a thermostat upstairs. Keep it set to keep the 3rd floor comfortable. Cold air will continue to sink to lower levels, but that could keep the lower level AC unit from running at times.
We might see how this approach works this summer, but based on similar attempts in our prior home I don't hold out much hope. I'm thinking of ways to take care of the problem while we still have parts of the house torn apart.

wilked
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Re: Third floor too hot with central A/C: options?

Post by wilked » Fri Feb 23, 2018 2:26 pm

We have similar setup:

New england climate, old Victorian house, finished attic (finished into three rooms, bathroom in middle).

We added central / heat pump as part of the project so a little different. We have a 3.5 ton unit (house is 3 levels, maybe 2500 sq ft in total). Note that it only feeds 2nd/3rd floor (we didn't want to give up the closet space for 1st floor)

What is your tonnage?

Where is the air handler stored? Is it in a 'conditioned' space (ie in a temp-controlled space)?

First thing - there is a decent chance that your insulation in the roof is sub-par. As part of our project we spray-foamed the roof in-between rafters (6" closed-cell spray foam, R-40). That roof and area is tighhhht on heat entry/loss. I think that makes a massive difference - before that it was pink stuff in there and it got wicked hot in the summer. Cost about $5K (not cheap) but should pay itself back within 5-10 years.

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dm200
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Re: Third floor too hot with central A/C: options?

Post by dm200 » Fri Feb 23, 2018 2:30 pm

coalcracker wrote:
Fri Feb 23, 2018 2:12 pm
I am in the midst of a significant remodel of a newly purchased home. It has central heat and A/C, and a finished attic in which we are 2 large bedrooms, a landing, storage closet, and full bath.
We have noticed this winter that the central heat works well on the third floor, but were warned by the previous owner (as evidenced by a window A/C unit on the third floor) that the central A/C does not work well in the summer heat. We are in PA to give you an idea of the climate.
It seems like overkill to add another HVAC unit for a single floor. I have been reading about ductless Mini Split A/C systems, but they get pricey particularly with dual zone systems, which we would need with the layout of the floor. Because of some changes we are making to the layout of this floor, the current single window unit will not work well.
Any other ideas for improving cooling on this floor in the summer?
Have you personally experienced this AC issue yet? If not, perhaps wait to see how one AC season goes before doing anything expensive.

One thing to try is to keep the fan running all the time - not just when the AC is operating. That, sometimes, can "solve" the problem. I once rented a house where doing that solved the summer AC problem. I might also see if just some circulating fans to/from that area to the lower levels might help as well.

Insulating the area/roof might also help.

bloom2708
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Re: Third floor too hot with central A/C: options?

Post by bloom2708 » Fri Feb 23, 2018 2:36 pm

lthenderson wrote:
Fri Feb 23, 2018 2:22 pm
coalcracker wrote:
Fri Feb 23, 2018 2:12 pm
Any other ideas for improving cooling on this floor in the summer?
There are now a number of companies that make smart vent covers that essentially turn every room into its own zone. They replace your old vent covers and after you program them with your smart phone, open and close to maintain your desired temperature in every room. I don't have any so I can't vouch how well they work.
I checked into different smart vents. The sizing is often very limited and they are expensive. ~$5,000 to do most of our vents.

We usually end up with some strange days in the spring in fall. Start out in the 30s (heat) and come home and it is 80 (AC). How do you account for that? Well, you really can't.

A couple weeks ago, my wife was vacuuming the 3rd floor. She opened 4 of the top floor vents (unknowingly). It was very cold and I came home and it was ~80 upstairs and 67 in the basement. I closed up all the vents on the top level and it started to even out over a few hours.

Our next house will hopefully be one level. Even then, getting heat/cool air to the outer rooms is challenging at times. Mini-splits or multiple zones is the next step. Much harder to retrofit a house compared to doing it this way from new.
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dm200
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Re: Third floor too hot with central A/C: options?

Post by dm200 » Fri Feb 23, 2018 2:37 pm

Sometimes ceiling fans can help a bit as well.

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Epsilon Delta
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Re: Third floor too hot with central A/C: options?

Post by Epsilon Delta » Fri Feb 23, 2018 2:38 pm

coalcracker wrote:
Fri Feb 23, 2018 2:26 pm

We might see how this approach works this summer, but based on similar attempts in our prior home I don't hold out much hope. I'm thinking of ways to take care of the problem while we still have parts of the house torn apart.
Anywhere that is torn apart: Air seal, make sure the roof (or attic) is properly vented, and insulate.
For anywhere else tear it apart and see previous. :twisted:

Hot air does rise, but another reason that top floors get hot is that the black roof is acting as a solar collector and there is not enough thermal barriers between the roof and the living space.

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Re: Third floor too hot with central A/C: options?

Post by jminv » Fri Feb 23, 2018 3:24 pm

It sounds like the issue is that the HVAC was sized for the house when the attic was unfinished which is no longer the case (or was not properly sized). When prior owners went to finish it, they did not upgrade the HVAC system which they should have. Your HVAC system is no longer properly sized for your house. I would imagine the insulation is likely also lacking. I suspect this because I had experienced the same issue with an addition to a house I owned at one point. Prior owners had put in a bonus room which had been an unfinished attic in third floor plus a large addition on one side of the house. I first added new insulation to R-60 level as contractors had finished to a pathetic level (below R10). This helped some with heating but didn't make it as comfortable as the rest of the house. I fixed air loss issues. I also adjusted the air flow around the house as the addition had caused problems elsewhere in the house. I was about to install a new heat pump but instead I was moved and it became someone elses problem. This was the only real solution to the problem given the size of the addition and the current HVAC system.

Assuming you stay in the house long term, adding to the central HVAC system will pay off in lower heating and cooling costs because of it's much greater efficiency. I have experience with mini-split system units and they are not great. My main problem with them is their reliability, which is much lower than a central system. If you're staying shorter term, though, they are an option. They're ubiquitous outside the USA.

curmudgeon
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Re: Third floor too hot with central A/C: options?

Post by curmudgeon » Fri Feb 23, 2018 3:33 pm

For cooling, I might look into whether a booster fan is possible in the ducts going to 3rd floor. Maybe also see whether they need some better air return flow; if the floor is closed off by doors without a return vent, it will have higher air pressure and get less cool air flow out of the vents. Maybe doing something like trimming the bottom of BR doors or adding a vent panel in them or in a door at the top of the stairs.

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Smorgasbord
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Re: Third floor too hot with central A/C: options?

Post by Smorgasbord » Fri Feb 23, 2018 3:36 pm

My attic was finished off by a previous owner, and the ductwork up to there is a bit lacking so it also gets quite warm in the summer. The AC was replaced last year, and when I inquired about upping the tonnage, the company flat out told me that a small unit in the attic would be far better than trying to get the main system to blow enough air up to the attic to keep things cool. I've been thinking about adding something like in the following link.
https://www.menards.com/main/heating-co ... 070&ipos=6

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Re: Third floor too hot with central A/C: options?

Post by Shikoku » Fri Feb 23, 2018 5:45 pm

We got additional baffles and soffit vents installed to increase attic ventilation. This keeps the attic temperature little down which in turn helps with upper floor temperature in summer.
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Re: Third floor too hot with central A/C: options?

Post by madbrain » Fri Feb 23, 2018 9:40 pm

How big is the house, and how old is the existing central HVAC ?

In our 2.5 story, 4600 sq ft mansion in California, we went with Carrier Infinity system, with 2 AC and 2 furnaces. Grand total of 10 zones - 5 downstairs and 5 upstairs.

Carrier Infinity zoning works with dampers in the ducts - not "smart vents". Closing vents would be very inefficient and is not recommended. It would cause pressure issues and would not save you as much.

This was not cheap, but considering VHCOL location, it was $25K net after state rebates. This was done before we moved into the house as it was a very extensive project with ceilings open for a while. Very happy with the results. It's a very efficient system.

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Re: Third floor too hot with central A/C: options?

Post by mouses » Fri Feb 23, 2018 10:39 pm

bloom2708 wrote:
Fri Feb 23, 2018 2:36 pm
We usually end up with some strange days in the spring in fall. Start out in the 30s (heat) and come home and it is 80 (AC). How do you account for that? Well, you really can't.
I have that happen in my house. There are thermostats that control both heat and AC that handle this weird situation.

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FrugalInvestor
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Re: Third floor too hot with central A/C: options?

Post by FrugalInvestor » Fri Feb 23, 2018 11:00 pm

Is there any way to improve the insulation in the ceiling of the third floor? This should reduce the heat stratification in the house and even out the the temperature from top to bottom. Also, you might look into having an energy audit performed. In some areas these are subsidized by the utility companies. A good energy auditor should be able to suggest solutions to improve the situation.
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Re: Third floor too hot with central A/C: options?

Post by DavidW » Sat Feb 24, 2018 1:01 am

I live in the west coast and mostly dry heat. My 2nd floor is quite warm during summer and we use a whole house fan to draws in outside air. I am not sure if that is something that is common in your area.

With the whole house fan, you can only turn it on when outside is cooler. So, we don't go upstair until bedtime... So, it is limiting to what you can do but the cost is reasonable.

For me, it saves me hundreds annually by not having to run the AC just to cool the bedrooms...

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Re: Third floor too hot with central A/C: options?

Post by Sandtrap » Sat Feb 24, 2018 1:29 am

1 Foam insulate the attic. Might change things drastically.
2 Add a smaller A/C system just for the attic.

I have a 3 story home and there are separate A/C-Heat units with independent thermostats for each floor. Works great. Saves $$$ with a zone system.

j :D

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Re: Third floor too hot with central A/C: options?

Post by Dudley » Sat Feb 24, 2018 6:38 am

Has the refrigerant charge/pressure been checked in the AC unit ?

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mrc
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Re: Third floor too hot with central A/C: options?

Post by mrc » Sat Feb 24, 2018 8:34 am

Our second floor gets hot in the summer. House has the feed plenum for 2nd story in the attic, and flexible duct to ceiling vents in the rooms. he central return in the hallway. So no closing doors. This has to be the worst idea ever. HVAC tech says there is no way to push cold heavy air from the basement unit up three stories, across a hot (but very well loose-fill insulated) attic, through these flex vents to the ceiling ducts.

The basement is not conditioned, so there are no vents to close there. When I tried closing some of the 1st floor vents to push more air upstairs, the evaporator coils froze due to reduced air flow.

HVAC tech says the house should have been dual zoned. DW won't tolerate a window unit in the bedroom, so for now, we just sweat it out. There is a special place in hell for builders that scrimp on HVAC when building new homes.
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Re: Third floor too hot with central A/C: options?

Post by scifilover » Sat Feb 24, 2018 8:46 am

Is there a return air line from the 3rd floor? Without a return from that floor, it is going to be very difficult to cool it. Thermostat usually on first floor. Cold air sinks, so thermostat reaches desired temp before 3rd floor cools.

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dm200
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Re: Third floor too hot with central A/C: options?

Post by dm200 » Sat Feb 24, 2018 10:51 am

. DW won't tolerate a window unit in the bedroom
Don't know if it makes any difference, but there are units that sit on the floor and just have the small in/out vents in the window. Perhaps an adjoining hallway near the door might help.

3feetpete
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Re: Third floor too hot with central A/C: options?

Post by 3feetpete » Sat Feb 24, 2018 11:34 am

Ceiling fans make a world of difference. Another thing you could try is insulating some more around the ducts and installing a booster fan in the duct just before it enters the room. Amazon has them starting at $16

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Re: Third floor too hot with central A/C: options?

Post by Scrapr » Sat Feb 24, 2018 12:12 pm

FrugalInvestor wrote:
Fri Feb 23, 2018 11:00 pm
Is there any way to improve the insulation in the ceiling of the third floor? This should reduce the heat stratification in the house and even out the the temperature from top to bottom. Also, you might look into having an energy audit performed. In some areas these are subsidized by the utility companies. A good energy auditor should be able to suggest solutions to improve the situation.
This. We had a bonus room above a garage that was always too hot or cold. We had knee walls on the sides. Energy audit done and we did a bunch of air sealing. Made a big difference. In the bonus room the pink insulation in the knee walls was a good filter for hot/cold air. But not a good barrier. Put a barrier (Tyvek I think) plus some sealing at top/bottom plates and made all the difference in the world.

The energy audit really helped

just one man's experience

CurlyDave
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Re: Third floor too hot with central A/C: options?

Post by CurlyDave » Sat Feb 24, 2018 11:17 pm

coalcracker wrote:
Fri Feb 23, 2018 2:12 pm
I am in the midst of a significant remodel of a newly purchased home...
What work are you doing?

If possible, the very best passive things are:

1. Attic insutaltion -- pay particular attention to insulation around the edges of the roof. Many contractors skimp there and it is surprisingly large percentage of the total area.

2. Attic venting

For a 3-story house, the typical residential HVAC system is going to be overwhelmed and just not work as well as it should. The mini-splits, or a separate HVAC system with two zones many make the upstairs much more livable.

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