Moving warm air: how to make use of my forced hot air ducts?

[NH_Wood]

Hi all!

So...wondering how to make use of my forced hot air duct system to pull cold air to the basement, while helping to move heat from the wood stove around the home. Do I put the thermostat on 'fan mode' and close all heat registers - allowing the cold air return to pull cold air to the basement? My cold air return is located centrally in the home, about 2 meters from the wood stove. Hoping for some advice. Also - if this set up does not work, should I think about putting a cold air return in a distance first floor bedroom? If so, what does this entail? Thanks in advance! Cheers!

 

[LLigetfa]

My cold air return is located centrally in the home, about 2 meters from the wood stove.

I believe code requires the stove to be 10 feet (3m) from the cold return. I doubt running the blower would work for you but you are free to try it.

Air in the ducts need to be able to complete a circuit and it is generally difficult to make air go where it doesn't already want to go naturally. The best you can usually do is assist it along its path.

 

[pyper]

My return is on the other side of the room from my stove. Maybe 15 feet (4.5m). If I turn the fan on and leave the registers open, then it blows the heat into the other rooms.

Not much, but I can measure a difference.

If it's 85F in the stove room, then the air coming out of the furthest register is about 70F If the room with that register starts at 53F, it will eventually get up to 58 or 60. To me, getting out of bed when it's 60 is much nicer than when it's 50.

 

[Northern NH Mike]

I've been thinking about the same thing for the past year and will probably think about it for another (I'm hesitant to cut holes in the floors/ceilings unless I absolutely sure it will work). The benefit of a cold air return is the passive nature of it. If positioned well it will work w/o electricity. Consider how much heat you will lose when you circulate it through the air ducts. Mine would have to go through a 45 degree fieldstone foundation basement. Even insulated, the duct work in the basement would bleed too much of the heated air to make it worthwhile. It is certainly worth the experiment however. Get a few cheap thermometers and place them around the house. Get a baseline temp in each room over the course of a day or two and then record temps with the furnace fan running and see what you get.

 

[pyper]

My ducts are in an un-insulated crawl space. It's probably usually 55 in the winter.

I think it's noteworty that in order to see a positive result I needed a 30F+ temperature differential between the room with the return and the cold room.


Here's something "funny" I get almost as good a result when the bathroom exhaust fan is on. It's in the back of the house too, and as it draws cool air out of the bathroom it's replaced by relatively warmer air in the next room, and so on.

I've actually considered opening the window in the furthest room from the stove and putting a box fan in it -- I'd be blowing 55F air out of my house and into the 20F outdoors, but it would pretty quickly draw warmer air from the vicinity of the stove. I'd probably need to crack a window somewhere strategic. This wouldn't be especially efficient and it goes against my nature to waste things so wantonly, but if I have wood that's going to go to waste anyway...