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?
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.
I don't think you need ducts, just holes in the floor.
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.
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
Am I complicating this too much?
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
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.
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.
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.
As others have said, breaching ceiling fire-barrier may be
code-violation. OTOH, for adjacent rooms, you might look at something
like http://www.suncourt.com/thruwall2.html . If I'd found this in
time, maybe I'd have put in a couple. With filters.
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