Heat basement with warm attic air

[thelooch]

I have a below ground basement which is always cold unless you turn the heat on. Even on a warm summer day you need to turn on the heat to bring it up to a comfortable temperature. It's well insulated, but the sun doesn't hit any of the wall to warm it up.

As I crawled around in my attic the other day the heat was almost unbearable. It was 30 degrees outside and must have been 45 in the attic. I was thinking to myself, why can't this warm attic air be used to heat the basement? I think all you would need is a vent running from the attic to the basement with a fan pumping the air through it. The drawbacks I could see to this system are that there is fiberglass dust in the attic, the system would only work in the summer, and the air in the attic seemed to smell funny, although it may have just been the heat.

Has anyone ever tried to implement such a system?

[larry]

we had a local guy try a similar thing last summer. He ran two 12" pipes from the crawl space (under house) to attic, to "swap" cool foundation air with hot attic air, to reduce air conditioning load. And added a 3/4 hp blower. Result: worked great for about 30 minutes, then the floors started to get warm ;-) he has good mechanical skills, just needs the math to work out these things, or nick's phone number!

-larry / dallas

[Shopdog]

I wonder if you were to get insulated round duct, the kind that has the spring in it. If you were to run this down to your basement and have a blower attached at either end. My thought would be to have the blower in the basement (only due to the hight heat in the attic) I would also build an enclosure for in the attic, attach the duct to one end of the enclosure and have the other end fitted for a filter (to remove dust and fibers) I think this is doable! Great idea too! I have a woodshop in my garage and thinking about this, maybe this would work for me. Seeing that the heat rises and the second floor of my garage is heated (its another workshop and rec room up there) I wonder if I could bring enough warmth down to the shop to make it comfortable.

Searcher

[Tomes]

I would be concerned about humidity issues. Tomes

[Edwin Pawlowski]

Comfort depends on the temperatures, but it will bring down the heated air and is certainly worth the minimal effort required. . May be just as cheap to run a second heater though. It certainly won't be free. (except in summer)

[nicksanspam]

It can, altho it may condense water in the basement if its dew point temp Tdp = (T+460)/(1-(T+460)ln(RH/100)/9621)-460 is higher than the basement temp. For instance, 70 F and 50% makes Tdp = 530/(1-530ln(0.5)/9621))-460 = 50.5 F, with condensation on 45 F basement walls. Then again, that warms the walls. With enough airflow, they will warm to the dewpoint and the condensation will re-evaporate. Without enough airflow, the basement will gradually become an aquarium. We might avoid this with a "differential humidistat" that only moves air through the basement when it contains less absolute moisture than basement air, eg a Smart Vent (tm.)

My basement has a $5 humidistat and a $12 window box fan near the floor that pushes air up through a duct to the first floor when the RH of the air near the floor rises to 60%. Yesterday, I washed some clothes and hung them to dry in the basement. The fan is running this morning, for the first time this year. T = 65.5 F with RH = 69% on the first floor. The outdoor temp is

51.0, at 6:30 AM. This might be a good time to run a dehumidifier to warm the house. Or wait till outdoor air warms up later today, and open a window. If it were hot and humid outdoors, a window AC could help, with additional net house cooling from the basement.

An attic with a transparent south roof can collect lots of heat, as in our Soldier's Grove Solar Today story at

Nick

[FixerDad]

This is something I've thought of as well. You would need two ducts, supply and return, otherwise you'd draw air into the attic from the outside, which would make the whole thing useless in the winter. Using a filter over the intake in the attic as someone else mentioned is a necessity. It must be pleated hepa grade to ensure no attic contaminants move thru the house. Bigger is better than smaller- lower resistance, longer maintenance cycle. A bit more $ up front, but can be vacuumed clean many times with care. Use a fan/blower that's just large enough to move the air at a reasonable rate. You'll have to figure out for yourself how to control the on-off cycle. If you have predictable sun in winter, a photo switch might do, or a timer or ? otherwise. There should also be a filter on the return in the attic, as there may be times/conditions when the fan is off that you get air going down that way. All of this depends on if/how well your attic is ventilated and other "local" conditions.