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re: cold air return/wood stove
2 nov 2004
hayduke  wrote:

>i have a wood stove... in our basement... the only route the warm air
>can take to get upstairs is, the stairway... 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)

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 :-)

>would putting a cold air return in a corner or two of the home solve
>this issue?

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. 

>if so, how many might i need?

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.

>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?

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


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