Moving Heat/Will This Work?

[RobJob]

I have a small cabin with a small Lopi woodstove/freestanding. It's made to run wide open to reduce the emmisions by recirculating the super-heated air in the stove. Works great! Consequently, I get a lot more heat than I need sometimes.

Question: If I built a sheetmetal hood over the stove and ran 6" sheetmetal duct off of it with a fan in the pipe to push the warmed air back down to the room I am building underneath (that's another story), how well can one expect the warm air to flow down?? It would only have to go directly underneath where the stove is. I was also thinking of pulling the cool air from below back up to the heated room above. Also, how many cfm fan would you recommend? I guess the bigger fan the louder. Maybe with a rheostat?

I know the logical solution would be to put the stove on the bottom floor and let the heat rise, etc. Well, things didn't really evolve in a particularly logical order. I have been searching for some references to what I am thinking of and I have not found anybody ever trying to do this and posting there results on the web anyway. Just wondering what some of the more engineering inclined folks think or if you have seen anything along these lines. Thanks for your thoughts on this. Rob.

[grumble]

It should work, I'd think. I'd put the fan in the room you spend the least time in, just for the noise reduction.

Nothing you do to push hot air downward will be especially efficient until you get to pretty fast air movement. If you want the temp to be close to the same in both rooms, it will take a fairly large fan.

[offgridbob]

On my job we take apart a lot of huge computer banks that have all sorts of fans in them. some are 110 some 24 volt and some 12 volt. all are quiet and they range from 8,6,4,2,inch in diameter. Most are less then an amp to run. Send me a PM with type your looking for and if I can just get the mailing fee I may be able to hook ya up

[krapgame]

Here's something for your consideration. What about if you used a vertical stack of duct or something equivalent to within a foot or so of the ceiling and put the other end through the floor into the lower room. Use 2 fans, one in each end of the duct, with the upper one pulling hot air from the ceiling into the pipe and the lower one blowing it out into the lower room. Granted, it wouldn't be the prettiest thing to have in the room, but if it worked out you could frame it in or put a plant in front of it or something. Similar in concept to your idea, but maybe easier to implement and later conceal if aesthetics are an issue. Also, you could probably rig some kind of thermostat controlled rheostat that would speed up the airflow as the temperature increased.

I think the hood idea should work as well, but I think I would use 2 fans, especially with all the 90 degree bends that would be required, if I understand your idea correctly. Either way, I think I'd run your ductwork down pretty close to the floor of the lower level or else the air will stratify near the lower level ceiling and not really warm the lower level too well.

[12vman]

Do you have enough headroom in your stairway that goes from the upper floor to the lower level to build some type of a duct? Wasted space anyway. I assume the ceiling of the stairway blends to the ceiling of the upstairs?

A fan to push air down the duct and possibly a ceiling fan in the lower level to move things around? Just a though..

[RobJob]

Well, there is no stairwell, on the inside at least. There is a stairwell up to the loft from the main floor that is heated. I will have stairs on the back porch down to the lower level.

The reason I was going to install a hood a few feet over the stove was that when the stove gets cranking, as small as it is, it is really putting off too much heat for a little 14X16' room and loft. Ducting from the hood to directly below will be about 12-14' run to the floor below. Two fans? I was considering another duct/fan in the opposite corner to push cool air back up creating some cross circulation. I will have plenty of opportunity to tinker with it all.

On an almost totally unrelated topic, since you mentioned stratification, I have been pleasantly surprised that there is very little stratification from the main floor to the loft when things are warmed up. Why? I think the 1" of ridge vent I left across the top of the loft ceiling lets just enough of the warm air out to keep things moving. Everything is well insulated and I needed some way to allow moisture to escape so I left a gap at the peak of the ceiling and screened it good to keep bugs out. It sure seems to work. Not to sure how I will vent that bottom floor? Probably just make a vent throught the ceiling/floor somewhere.

[MooseToo]

i think i would also try the ducted shroud idea - but - i'd run the duct from the lowest part of the lower level (which should be the coldest air in the house) into the shroud and install the fan at the bottom end of the duct - i would not rig a second fan to blow air down into the lower space until an experience factor of this set-up is obvious -

[keydl]

Heat rises and it takes power to force it down - the make 2 forms of duct fans and you can use a blower from the top of the hood or the top of the room, a hood is not needed. One thing not mentioned is a return of twice the square inches min to the powered duct.

Positioning a blower above the stove will grab the hot air rising off the stove and power it through the duct to the bottom of the lower room - where the air flow will stir the air and the mixed air will go some place, a return duct if you put one in or out of the building if you don't.

A fan has little tolerance for backpressure and the air flow will slow a lot when you need it the most, they are not intended to power ducts.

[RobJob]

Thanks for giving me some things to ponder. Like balancing the air flow. Didn't know one needed twice the return capacity. I think a hood is needed because when the stove gets cranking it is really putting off much more than needed and just pulling it off the ceiling is letting too much into the room to start with. Hasn't been a huge problem so far...I just open the doors and windows! But I haven't had that space below to heat either. Thanks!

[grumble]

Rob, I hate to throw a wrench in the project now, but maybe moving all that air with ducts and fans might get a bit unwieldy in a small house. How about a heat exchanger?

If you look around, you can find some coils from junked refrigerators and/or air conditioners. Use one at the stove and the other in the basement. Plumb them together with a reservoir for expansion and a small 1/4 HP pump to move the fluid (antifreeze?).

The coil at the stove could be put behind the stove, out of sight between the stove and the heat shield.

Just another idea. I wouldn't want all those hoods, ducts and fans, personally.