Take the 2-minute tour ×
Home Improvement Stack Exchange is a question and answer site for contractors and serious DIYers. It's 100% free, no registration required.

I am installing a new wood add-on stove in the basement and want to hook it in to my forced air furnace duct work to help move the air in the house. I have heard it can be done, but I am confused as to how or where to hook up the hot air pipe. Some say to hook it into the cold air return, but what about CO2 build up? Others say you can hook in to the output side and run it through the furnace, but I was told that could ruin the forced air furnace, and that I would have to put dampers in to by-pass the electric furnace altogether.

So I am confused. Can some one help?

share|improve this question
    
Some pictures of this stove would be helpful. Make, model so we can check out their website would help with giving advice. From your post, for some reason, I get the image of someone hooking the stovepipe coming out of the firebox into the HVAC duct expecting it to heat the house, which it would, probably momentarily and quite spectacularly. Is this stove actually a wood furnace with separate air jacket that connects to ducting? –  Fiasco Labs Dec 1 '12 at 17:07
1  
While CO2 can be dangerous when it displaces oxygenated air, what you really should be concerned about with any fuel burning appliance is CO - carbon monoxide, an odorless, tasteless, invisible, highly toxic gas. Just sayin'. –  bcworkz Dec 1 '12 at 19:06
add comment

2 Answers

I will assume this wood stove has a proper air jacket from which heated air can be drawn? The possibility of dangerous gases infiltrating into this jacket is a valid concern and entirely dependent on the integrity of the firebox. This can only be done by careful inspection and possibly some sort of pressure test. In theory, this can be just as safe as any other fuel burning furnace.

The purpose of piping the stove's heated output air to the furnace return air is that the furnace is then fed pre-heated air. This minimizes the amount of energy the furnace must use to raise it to the proper distribution temperature. It doesn't make sense to apply the wood heated air to the furnace circulating air unless the furnace's output temperature was deliberately reduced, relying on the wood heat to make up the difference. This would be very difficult to properly regulate since thermostatic control of a wood burning appliance is marginal at best unless you are burning wood pellets.

Whether the pre-heated air from the wood stove is bad for the furnace would depend on just how hot this air is. This is highly variable depending on air flow, fuel wood type and loading, as well as combustion air or damper volume. With adequate air jacket flow and typical wood stove firing practice, I don't see this being a problem for the furnace. But there's a lot of variables. It would be easy to misfire the stove and reach damaging temperatures.

Some sort of damper bypass system would be ideal, but the controls needed would be complicated to ensure adequate heat was delivered regardless of the stove's firing rate. Even then, it will require careful monitoring. It'll always be possible to over fire the stove during low heat demand conditions, wasting fuel.

share|improve this answer
add comment

By hooking to the return of the furnace you are feeding hot air to the furnace; once it hits the temp limit switch the furnace fan will kick on and essentially you will have two blowers blowing the heat. This works very well to supply the entire home. If you connect it to the supply side and high temp hits the furnace fans limit switch, the two fans are going to fight each other. Most furnace fans have different speeds: a lower setting for heat and a higher setting for a/c. My suggestion would be to hook up the wood stove to the return air and go to the gas furnace thermostat and turn the fan to the on position using your forced air furnace into a air handler: this should help keep the air being dumped into the furnace from getting too hot. Remember the furnace is designed to grab cool or (room temperature) air and in the last step, heat it and dump it into the duct, so you should attempt to keep that air from getting too hot. It should also mix the air by sucking additional air from throughout the house via the cold air returns. One thing to check would be to make sure the CFM rating of the furnace fan is larger than the CFM of the woodstove fan.

share|improve this answer
add comment

Your Answer

 
discard

By posting your answer, you agree to the privacy policy and terms of service.

Not the answer you're looking for? Browse other questions tagged or ask your own question.