# Is it possible to use ductwork to move the warmed air from wood stoves?



## Suji (Oct 24, 2013)

Once upon a time there was a cellar furnace in this fixer upper farmhouse. The furnace use was discontinued because the unfinished cellar floods in extreme rains and everything metal will rust in the damp the rest of the time. So, the house went to zoned electric heat in every room, not all of which work downstairs. Meanwhile there is ductwork left in the ceilings from the old furnace days with (plugged up) registers in the rooms. If a high BTU woodstove was placed at the back of the large kitchen wing (where the ductwork is accessible)  is there some way to move that heat in the wing through the old ceiling ductwork to the main house registers? Is a furnace the only thing powerful enough to do that?  My house layout complicates heat flow since there is no place to put a stove centrally. Meanwhile, I have no to substandard heat in 3 main rooms downstairs without replacing baseboard heaters and thermostats from the 60's or using space heaters.


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## begreen (Oct 24, 2013)

Heat loss in the ductwork to the cold basement would probably negate any gains. If we can see a floorplan sketch we may be able to make a suggestion.


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## HotCoals (Oct 24, 2013)

You might need a couple wood stoves.How big is the place?


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## Backwoods Savage (Oct 24, 2013)

It is very rare to hear of anyone having any luck trying to move air through duct work.

On those rooms that are not getting heat, have you tried fans? The best way with fans is to use a small fan, placed on the floor and running on low speed. Try setting the fan near those colder rooms and aim the fan toward the stove, not toward the rooms.


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## Suji (Oct 24, 2013)

There's no longer any ductwork in the cellar. What remains runs through the kitchen wing into the adjoining room with ceiling "registers" there and floor "registers" for the two bedrooms above. The kitchen wing is two rooms separated by a wall, so 24x25 and 11x25. The adjoining room (I call it the gathering room-front door opens into it, open stairs) is about 21x26 with a currently unheated gutted bedroom at the bottom of the stairs 17 x 18(used to have ductwork coming from cellar to heat it).  Ceilings are 7.5 feet. 225 year old log based house. Insulation not great--old leaky house but coldest in the kitchen wing from NW winds and cellar below.  There's a great room wing off the gathering room as well with cathedral ceilings--I just drop a blanket down over the doorway to keep the heat in there.  No hearths or working chimneys-just remnants. No wood burning or pellet stove yet--just intent to do something.

My DH seems to think he is going to be able to find technology available in either a fireplace/insert or stove to utilize that open ductwork in the kitchen wing. Is there truly nothing like that available or is it that no one is happy with the outcome heat or safety wise?


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## BrotherBart (Oct 24, 2013)

When my office was in the basement I knocked the cap off of the ductwork right next to the stove and put a duct fan in it trying to move the heat upstairs. Miserable failure on that one.


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## thundar (Oct 25, 2013)

I have to disagree with some of the guys on Hearth who have said you can't move air with your furnace fan. I'm doing it right now with good success.  The key is having enough cold air returns in the vicinity of the wood stove so the furnace can pull the warmest air.  I have a Jotul Oslo on the main floor of our ranch home, and we have an almost full basement. I have watched the temperature in the basement go up while I run the furnace fan. We have a newer thermostat that in addition to being able to tun the fan on, allows me to select "circulate", which automatically cycles the fan on and off (the fan runs about 30% of the time). Our upstairs stays in the 70s, and the downstairs in the mid to upper 60s.  If it gets too hot upstairs, I turn the thermostat to just "fan on", and it will really heat up the downstairs. If you were moving air to an upper floor, it would work even better. The key is having enough cold air returns.


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## USMC80 (Oct 25, 2013)

I'm still yet to try it with my furnace fan.  Will give it a go when it gets colder.


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## daleeper (Oct 25, 2013)

You can see through the responses given that moving heat is not easy.  Stoves are space heaters, and to expect anything more than that can lead to disappointment.  Some get lucky and are able to get heat moved to where they want it.  There are many posts on this forum looking for help getting heat to move where they thought it should have moved easily, myself included.

If it is a choice between a stove and a furnace, get the furnace if you want to get heat moved into difficult areas, or get more stoves.


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## jeff_t (Oct 25, 2013)

Suji said:


> My DH seems to think he is going to be able to find technology available in either a fireplace/insert or stove to utilize that open ductwork in the kitchen wing. Is there truly nothing like that available or is it that no one is happy with the outcome heat or safety wise?



There certainly are wood burning furnaces available, that function as a central heating system, and use ductwork to distribute heat thru the home. Whether one will work with what you have depends on, what you have.

For example http://www.drolet.ca/en/products/wood/drolet-tundra-furnace

There are also high efficiency, zero clearance fireplaces that use blowers to move heat, and some of them have provoisions for ducting heat to other rooms. Those can get pretty pricey.


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## thundar (Oct 25, 2013)

Like I said, earlier, I have had success moving air with my furnace while using my wood stove.  I also have a whole house wood furnace (indoor - Clayton), and it 
does a better job of keeping all the rooms in the house at a consistent temperature - however - it uses almost twice as much wood.  With the addition of my Oslo this fall, I plan on 
only using the Clayton when necessary.


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## Lumber-Jack (Oct 25, 2013)

I've had great success using my furnace ducts and blower to move the heat around in my house. yet I've heard of quite a few people not having success, and had trouble understanding why that was until I realized that many homes in the US have their duct work running through un-insulated space. (eg. in the attic, through un-insulated crawl spaces, etc...) 
There are a lot of reasons why ducting might not work as well as it aught to, but it stands to reason that if your duct work runs through any areas where they are exposed to outside elements, and not contained within the insulated envelop of the house, then you are going to have heat loss, plain and simple. On the other hand, if you have two rooms, room A and room B, and the air in room A is 100 deg, and air in room  B is 50 deg, and you force the air from room A directly into room B (without exposing it to the cold outside), and allow the air from room B to flow back to room A, then the laws of physics dictate that the temperature in room A will decrease, and the temperature in room B will rise.
Of course for obvious reasons, to get the most efficiency out of duct work you would want the exit (or return) air duct in the warm room to be located near the ceiling, and the exhausting duct in the cold room to be located near the floor. If you have it the other way round, it's not going to work very well.
They do install cheap stand alone furnaces in small homes, they function much like space heaters or wood stoves and they generally try to locate them centrally in the home to get the best heat distribution, but for larger homes and building HVAC designers almost always rely on duct work to distribute and regulate the air temperature.


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## mellow (Oct 25, 2013)

I am able to use the recirc fan on my system as well,  but the key is I just had my R8 duct work put in a few years ago so it is able to transfer the heat very well.   Having the return in the same room as the stove and having insulated duct work are two important factors.

I check my registers in the other rooms via an IR gun and get 76-78 degree air blowing out of them which is plenty to keep the other rooms warm.  BUT I am also going sideways,  not UP, I think that is a factor as well.


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## tahoostas (Oct 25, 2013)

Another consideration is a fresh air line. Our house had a section of return air pulling outside air in, I guess from when the furnace was still an oil burning one before changing to electric. Sucking -20*C air sure didnt help!  I removed that section and will see how it does this year.


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## akbear (Oct 25, 2013)

In my mind most people attempt to reverse things by trying to push hot air to remote places (which will lose volume and pressure as it cools down on the trip) instead of pulling cold air in from the extremities.  A forced air furnace only works because cold air is being pulled into the furnace to be heated, and the lower pressure in the rooms with the cold air returns helps the warm air in the ducts to get to it's destination (and remember too, which side of the furnace is the blower?  On the cold side).  

If you had a room without a return and just a outlet for the heating ducts, the room would remain fairly cold even though some heat is getting to it, for example, in my ma's last house before she passed away a new furnace was installed in the garage with a fresh air intake for combustion, and obviously one could not have a cold air return in the garage that would pull potential fumes into the house, so the two or three registers blowing (far too strong of a word for the amount of heated air that came out of them) warm air into the insulated garage were only enough to keep the garage above freezing, usually in the 40s which was just fine for it's purpose and a small amount of fresh air to make up for the loss was likely being drawn in through the crawlspace, which preheated it during it's journey from outdoors. Same thing with the arctic entry, one heating register was installed there to keep it slightly above freezing, as otherwise being totally shut off it wouldn't have been much different from the outdoors in the depths of winter).  Often this same thing happens with bathrooms where people keep the door closed and don't use an exhaust fan, or the opposite situation where people try to save heat by turning off heat registers but neglect to cover the cold air returns, something's going to be sucked into those rooms by whatever the easiest means is.

So of course my suggestion if you are going to put some sort of blower in the ductwork near the stove is to suck cold air from the far rooms and let the house itself be the heating duct after the stove has heated and expanded that air.


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