[Use basement air to cool 2nd floor?]

Questions on how we spend our money and our time - consumer goods and services, home and vehicle, leisure and recreational activities
Post Reply
Topic Author
Mrxyz
Posts: 742
Joined: Wed Feb 29, 2012 6:12 am

[Use basement air to cool 2nd floor?]

Post by Mrxyz »

Hi all,

The basement temperature during summer is around 10F lower than the 2nd floor - so why not install a duct with a fan which moves air from basement to the top floor? I know, I know - I am probably wrong because it sounds too easy to be true. I guess air has to be displaced - that is there cannot be a vacuum created when air leaves the basement and perhaps that is the limiting factor.
Thoughts/ suggestions ?
(Engineers of the forum - this one is for you!)
Mr. Rumples
Posts: 1103
Joined: Sun Aug 25, 2019 7:16 am

Re: Basement temperature versus 2nd floor temperature

Post by Mr. Rumples »

I'm not an engineer, just a bit of a VA history enthusiast...we have all seen the cupola on Mt. Vernon. This was functional as well as decorative (alas, it also always was leaking). As hot air rose, it was exhausted out through the cupola; what we call today "passive cooling."

Even at the Constitutional Convention, George Washington was thinking about his cupola: "Let particular care be used to putty, or put copper on all the joints to prevent the leaking, & rotting of the wood as it will be difficult, & expensive to repair it hereafter..." George Washington to George Augustine Washington, Philadelphia 12th Augt 1787 https://founders.archives.gov/documents ... 05-02-0266

Up until the advent of air conditioning, large homes were built with a large central hallway which also functioned as a breezeway with a cupola. The cupola, the large central hallway and later the use of screened "sleeping porches" (our townhouse had a sleeping porch) made homes in the south tolerable by the standards of the day. It helped to keep moisture from building up and even helped dry hay in barns.

Modern roof ridge vents use the same principle. Perhaps it might work if you have a ridge vent and just open the attic door and basement windows.
Last edited by Mr. Rumples on Mon May 04, 2020 2:13 am, edited 7 times in total.
megabad
Posts: 3316
Joined: Fri Jun 01, 2018 4:00 pm

Re: Basement temperature versus 2nd floor temperature

Post by megabad »

Doesn’t seem to me like this would save much for most folks. How cold is basement relative to outside air? Also, basements are usually humid...
KT785
Posts: 398
Joined: Fri Jul 11, 2014 2:21 pm
Location: Texas Hill Country

Re: [Use basement air to cool 2nd floor?]

Post by KT785 »

At our previous house (we now live in Texas with no basement) I had an air return installed in the basement when we had a new HVAC system installed. Basement was 3/4 finished and already had air supply vents run throughout, but no air return. Purpose of the install was mostly to balance out the basement air, particularly in the summer when the basement was much colder than the rest of the house and likewise reduce the humidity since the basement air would actually more readily get back to the AC coils and dehumidify (and didn't need a standalone dehumidifier anymore).

Install went without a hitch and the basement started to balance out compared to the rest of the house--the second floor also was in better balance with the house too, but I attribute that to the new HVAC system with a variable speed fan and communicating/intelligent thermostat vs. the basement duct work.

Something you might consider if you're evaluating duct work changes is having a separate thermostat installed on the second floor; our Texas house (around 3,000 sq. ft.) has a single AC unit and furnace, but two thermostats that tell the system to direct airflow between the two floors as needed--it's a zoned system with dampers in the ducts.

KT785
ScubaHogg
Posts: 762
Joined: Sun Nov 06, 2011 3:02 pm

Re: [Use basement air to cool 2nd floor?]

Post by ScubaHogg »

Following with enthusiasm. Four story townhouse with a half basement. Easily 10 degrees cooler downstairs compared to upstairs in the summer, would love a better way to cycle the air upstairs.
“Unexpected Returns dominate the Expected Returns” - Ken French
BanquetBeer
Posts: 494
Joined: Thu Jul 13, 2017 5:57 pm

Re: [Use basement air to cool 2nd floor?]

Post by BanquetBeer »

I would check for radon first.
Designairohio
Posts: 80
Joined: Thu Aug 15, 2019 3:57 pm

Re: [Use basement air to cool 2nd floor?]

Post by Designairohio »

An A/C drops the temperature from the return to the supply ~20 degrees and dehumidifies the air
If your A/C was operating with only a 10 degree drop and not dehumidifying, most people would call for a service call
In most colonials the upper floor is warmer than the first floor Even with 20 degree drop and proper dehumidification unless the duct system is designed perfectly or there is a zoning system installed,
You would have to pump an insane amount of air upstairs to drop the temperature and would still be sticky due to high humidity
ScubaHogg
Posts: 762
Joined: Sun Nov 06, 2011 3:02 pm

Re: [Use basement air to cool 2nd floor?]

Post by ScubaHogg »

Designairohio wrote: Mon May 04, 2020 8:13 am An A/C drops the temperature from the return to the supply ~20 degrees and dehumidifies the air
If your A/C was operating with only a 10 degree drop and not dehumidifying, most people would call for a service call
In most colonials the upper floor is warmer than the first floor Even with 20 degree drop and proper dehumidification unless the duct system is designed perfectly or there is a zoning system installed,
You would have to pump an insane amount of air upstairs to drop the temperature and would still be sticky due to high humidity
Assuming the basement is temperature controlled as well, I’m thinking of this as something in conjunction with AC, not to replace it. A better central fan to equalize the temp so to speak, and then the AC to keep it comfortable.
“Unexpected Returns dominate the Expected Returns” - Ken French
rkhusky
Posts: 10909
Joined: Thu Aug 18, 2011 8:09 pm

Re: [Use basement air to cool 2nd floor?]

Post by rkhusky »

You do have to watch out for humidity. We would occasionally open the blower door to the 1969’s era furnace in the basement and just use the fan to blow a little cold air upstairs. But once we got a new system, we didn’t need to do that.

+1 for the additional thermostat and zoned system with automatic dampers.
hicabob
Posts: 3226
Joined: Fri May 27, 2011 5:35 pm
Location: cruz

Re: [Use basement air to cool 2nd floor?]

Post by hicabob »

It would work if you have a big enough basement. Case in point ....
https://www.atlasobscura.com/articles/l ... nditioning
Topic Author
Mrxyz
Posts: 742
Joined: Wed Feb 29, 2012 6:12 am

Re: [Use basement air to cool 2nd floor?]

Post by Mrxyz »

BanquetBeer wrote: Mon May 04, 2020 8:02 am I would check for radon first.
Yup, no radon, under basement ventilation system which runs 24/7, with 'normal' levels.
hicabob wrote: Mon May 04, 2020 9:48 am It would work if you have a big enough basement. Case in point ....
https://www.atlasobscura.com/articles/l ... nditioning
Very interesting read! Thanks.
I am still not clear if there is a way/need to replace the basement air, if it is possible to pump it upstairs.
neilpilot
Posts: 3553
Joined: Fri Dec 04, 2015 1:46 pm
Location: Memphis area

Re: [Use basement air to cool 2nd floor?]

Post by neilpilot »

An energy efficient alternative to A/C when the weather is borderline hot is to run a whole house fan in the evening, exhausting the air from the top floor into the attic. Keep the downstairs (not basement) windows open to inflow outside air, typically cooler in the evening, bring downstairs air up. A big advantage is cooling the attic space, lowering radiant heat from the upstairs ceiling and potentially also extending the life of your shingles.

This won't work in Memphis, since the shoulder AC season is too short and humidity is high (it's 98% humid now). However, it worked like a charm for me in upstate NY and northern NJ.

PS - basements are extremely rare in the Memphis area.
Last edited by neilpilot on Mon May 04, 2020 10:02 am, edited 1 time in total.
hicabob
Posts: 3226
Joined: Fri May 27, 2011 5:35 pm
Location: cruz

Re: [Use basement air to cool 2nd floor?]

Post by hicabob »

Mrxyz wrote: Mon May 04, 2020 9:52 am
BanquetBeer wrote: Mon May 04, 2020 8:02 am I would check for radon first.
Yup, no radon, under basement ventilation system which runs 24/7, with 'normal' levels.
hicabob wrote: Mon May 04, 2020 9:48 am It would work if you have a big enough basement. Case in point ....
https://www.atlasobscura.com/articles/l ... nditioning
Very interesting read! Thanks.
I am still not clear if there is a way/need to replace the basement air, if it is possible to pump it upstairs.
Maybe try a spot experiment by putting a large fan at the top of the basement stairs and letting it run for a couple hours and see if it changes the temp upstairs significantly?
User avatar
vitaflo
Posts: 1469
Joined: Sat Sep 03, 2011 3:02 pm

Re: [Use basement air to cool 2nd floor?]

Post by vitaflo »

We have the HVAC fan set to run for 15 mins every 2 hours. This just cycles the air in the house, so some hot upstairs air can move to the basement and some cool basement air can move upstairs. Basically it evens the temps in the entire house. Plus no worries about air displacement moving air only one way.
Alex Frakt
Founder
Posts: 11098
Joined: Fri Feb 23, 2007 1:06 pm
Location: Chicago
Contact:

Re: [Use basement air to cool 2nd floor?]

Post by Alex Frakt »

hicabob wrote: Mon May 04, 2020 10:02 amMaybe try a spot experiment by putting a large fan at the top of the basement stairs and letting it run for a couple hours and see if it changes the temp upstairs significantly?
I doubt this will do anything. The air that the fan is moving had to be replaced. Most likely it will be replaced by the air you just blew in, so you'll set up a very local circulation and won't actually draw up the cooler air.

For this to work you either need warm air to leave the house at the roof (and be replaced by relatively cool air at ground level) or air to be circulated through the whole house.

Edit: see vitaflo's post just above for an example of the latter
Mr. Rumples
Posts: 1103
Joined: Sun Aug 25, 2019 7:16 am

Re: [Use basement air to cool 2nd floor?]

Post by Mr. Rumples »

There are many articles online regarding passive cooling. While I don't have a basement, today I opened the windows and then held a smoke stick by the attic hatch while it was closed. The smoke did not go up. Then I opened the hatch and the smoke definitely rose as if there was a slight draft, though I could not feel it. I'm not sure what that tells me since opening the windows like that will only bring pollen in the house.

But my point is, and I am getting to it, is that after my aunt died in upstate NY, they found the basement behind the finished walls was riddled with black mold. Had she brought that air into the entire house there is no telling what would have happened.
tibbitts
Posts: 12532
Joined: Tue Feb 27, 2007 6:50 pm

Re: [Use basement air to cool 2nd floor?]

Post by tibbitts »

I'm not an engineer but I used to have a basement. Just to clarify this is a finished basement, correct? My basement was always humid, so it wouldn't have worked for me.
Topic Author
Mrxyz
Posts: 742
Joined: Wed Feb 29, 2012 6:12 am

Re: [Use basement air to cool 2nd floor?]

Post by Mrxyz »

tibbitts wrote: Mon May 04, 2020 11:33 am I'm not an engineer but I used to have a basement. Just to clarify this is a finished basement, correct? My basement was always humid, so it wouldn't have worked for me.
Yes, it is a finished basement.
Mr. Rumples wrote: Mon May 04, 2020 11:17 am There are many articles online regarding passive cooling. While I don't have a basement, today I opened the windows and then held a smoke stick by the attic hatch while it was closed. The smoke did not go up. Then I opened the hatch and the smoke definitely rose as if there was a slight draft, though I could not feel it. I'm not sure what that tells me since opening the windows like that will only bring pollen in the house.

But my point is, and I am getting to it, is that after my aunt died in upstate NY, they found the basement behind the finished walls was riddled with black mold. Had she brought that air into the entire house there is no telling what would have happened.
We do not have any mold / radon issues. But thanks for pointing this out!
Alex Frakt wrote: Mon May 04, 2020 10:50 am
hicabob wrote: Mon May 04, 2020 10:02 amMaybe try a spot experiment by putting a large fan at the top of the basement stairs and letting it run for a couple hours and see if it changes the temp upstairs significantly?
I doubt this will do anything. The air that the fan is moving had to be replaced. Most likely it will be replaced by the air you just blew in, so you'll set up a very local circulation and won't actually draw up the cooler air.

For this to work you either need warm air to leave the house at the roof (and be replaced by relatively cool air at ground level) or air to be circulated through the whole house.

Edit: see vitaflo's post just above for an example of the latter
Yes, that was my concern also as to how to 'move'/ displace air so that the cold air comes up. Easiest for me is to start the attic fan and that would remove or push out the attic air and (hopefully) move the basement air upwards (my house is quite air tight).....but not sure if any additional duct air movement was needed.
User avatar
TeamArgo
Posts: 131
Joined: Fri Jul 22, 2016 8:18 am

Re: [Use basement air to cool 2nd floor?]

Post by TeamArgo »

I am an Engineer who lives in a condo now, but up until 6 years ago I spent 25 years in a two story home with a basement. The basement was cooler and the second story (bedrooms) always ran warm. We had a laundry chute that led from the second floor hallway to the basement. I would place a quiet personal sized fan on a low setting at the bottom (I made a wire hanger for the fan right under the chute opening) and prop the cover open at the top for the four hottest months. It made a several degree difference when the fan was running. Return airflow passed down the stairs and under the door to the basement.
Until I did this, we would turn the thermostat down by two or three degrees at night for sleeping comfort, but afterwards this seemed unnecessary. I figure it saved about three to four bucks a week in cooling costs. The solution ticked many boxes for me: cheap, effective, low maintenance, unobtrusive, DIY. The only additional cost was for a laundry hamper, from which I carried the laundry down to the basement every few days to make up for the loss of the chute to my spouse.
“Love with your heart: use your brain for everything else.” -Captain Disillusion
Post Reply