Cold air return/wood stove

[Hayduke]

Ok, Here goes....

I have a wood stove as a primary source of heat( affordable heat, that is) and it is in our basement (Single story home with finished daylight basement). The only route the warm air can take to get upstairs is, the stairway. Aside from opening windows, there is no way for the cooler air ustairs to move and so it seems that the warm air in the basement is fighting to get by the cooler air upstairs, and the cooler air is just resting on the warmer air below. An inversion of sorts. (i'm waiting for a tornado to form in my stairway)

Would putting a cold air return in a corner or two of the home solve this issue? If so, how many might i need? And am I correct in assuming that a cold air return has to go from the floor upstairs(like a vent in the floor)to the floor downstairs(ducted to a vent near the floor)? Will this get the air moving?

Am I crazy?

Hayduke

[nicksanspam]

You might have a horizontal tornado, with cool air flowing down the lower part of the stairwell and warm air flowing up the upper part :-)

That would help. It might also help to raise the warm air outlet from the basement, eg close the stairwell door and put a large supply grill in the upper part of the door or the stairwell wall near the ceiling. In the latter case, you might add some thermal mass below insulation in the basement ceiling and turn on a window box fan on the stairwell side of the grill with a room temp thermostat.

That depends on the amount of heat Q you need to move and the height difference H between the supply vent and the stove and the temp diff dT between the basement and the upstairs and the minimum vent area A.

Moving Q Btu/h of heat requires A = Q/(16.6sqrt(H)dT^1.5) ft^2 of vents. If your house needs 50K Btu/h of heat and H = 8' and the basement is 80 F and the upstairs is 70 F, A = 50K/(16.6sqrt(8)(80-70)^1.5) = 34 ft^2, eg

68 6"x1' vents, with natural convection vs a fan. Q = 20K Btu/h and H = 16' and dT = 90-70 F makes A = 3.4 ft^2, eg 7 6"x1' vents.

Home Depot sells inexpensive brass-plated grills in 2-packs for areas with low foot traffic. Remove the dampers and install them around the house perimeter. Drill 4 holes in the carpet and flooring and cut out a rectangle with a Sawzall, avoiding wires and pipes and floor joists. Drop the grills in the holes and secure with a couple of drywall screws.

Sure.

I don't think you need ducts, just holes in the floor.

Nick

[Edwin Pawlowski]

Correct, it works well and I've seen a few homes like that. I also understand it is now against fire codes to have an opening above a stove. Makes sense if the stove would start blazing.

You can get good air flow up and down a stairwell. In my case, I had a 10" fan hanging in the doorway of the family room where the wood stove was. It was aimed at the stairwell and moved a fair amount of air. While not as good as the holes in the floor, it did work. Just one vent at the far end of the house would help the cool air drop.

[SQLit]

where is your furnace? Basement? Do you have ducts in the basement? If so maybe turn on the "fan" on the furnace it will stir up the air.

The stair well will naturally stratify, hot on top and cooler air will travel close to the floor. By heating the basement the floor will get warm over time and that in turn will keep the home warmer. sort of like an slow heat sink Cutting holes for faster transfer could be an violation of the fire code. Better check locally before doing so.

[Hayduke]

There is no furnace and no ductwork of any kind. The house's primary source of heat is a wood stove. The stairway is open(no door). There is no way for air to really 'circulate'. they (hot and cold air) have to pass eachother in the stairway, or like you say, convection/conduction will eventually heat the entire house assuming I can keep a fire going constantly for a few days which isn't always reality. It just seems like it would happen faster if the air had another route to the basement instead of the 'airs' having to pass eachother in the stairway.

Hayduke

[Hayduke]

I was concerned that in a very warm basement(which it can get pretty warm) the warm air will try to rise through any means available, and by just having a vent in the ceiling/floor, the airs(hot/cold) would again be fighting eachother to get by. If the return vent is ducted all the way to the floor in the basement, hot air in the basement would not be low enough to try to get upstairs through that vent therefore allowing the cooler air near the floor upstairs to drop through the duct and be sucked out downstairs to replace the warm air going upstairs...blah..blah..blah.

Am I complicating this too much?

Hayduke

[Edwin Pawlowski]

If you have holes in the floor at both ends of the house, one near the heat, one away, you will get a natural floor of air. If you take a candle to the stairwell, you will see the flame going in one direction if you hold it high, the opposite as you bring it down.

In my case, I have 2000 square feet to heat. Wood stove is at one end in the lower level. There will be a 10 or 15 degree temperature difference if rely just on natural convection in the central stairwell. With a couple of fans to move the air, it can be cut in half. With vents in the floor it would be even better. No need for the return ducts to reach the floor.

Use the candle to find the natural currents, then boost it with a small fan or two.

[Oscar_Lives]

I installed a duct with a small electric duct fan in it to move the warm air upstairs from the woodstove. I installed a return grill above the woodstove, ran the duct to the fan, then duct to a supply vent that I installed on the other end of the house in the hallway. The fan would draw a steady silent breeze of warm air to the upstairs bedroom area and it made a very noticeable difference.

[John Barry]

As others have said, breaching ceiling fire-barrier may be code-violation. OTOH, for adjacent rooms, you might look at something like

If I'd found this in time, maybe I'd have put in a couple. With filters.

John