# Add on Wood Furnace......is this gonna work



## sambrent18 (Nov 30, 2010)

Hi,
First let me say great site, I love it, very helpful.
Ok, I have a us stove hotblast add on wood furnace (1537) the 2500sq ft model.  I had a heating and cooling guy come out today and give me an estimate to hook it all in with my current electric heat pump and ductwork.  First qustion is I have the fiber board duct for my main trunck line, is this ok to use or should it be metal?  Heating guy said if it works now why change it.  Second I thought the wood furnace should be tied to the cold air return but heating guy said he can build me a box on the back of the furnace with a filter and that should be fine.  Finally, my air ducts from the stove will be tied in at the end of the main trunk line meaning it will have to push about 30ft of trunk with abou 8 or 9 flex lines off of that, (its the only way I could set it up because of my chimney.  I guess I am just looking for some advice or suggestions to see if this will work and be ok set up this way.  I am going to call us stove tomorrow to see if its ok to run this furnace into fiber duct I dont know about codes, I cant find anyone that does.

Thanks


----------



## geoxman (Nov 30, 2010)

I have a few flex duct runs and I have never had a problem I do not know about fiber board. Mine are in there after a few 90's and about 15 feet of a metal run? What did US stove say?


----------



## laynes69 (Nov 30, 2010)

When installing a wood furnace, all of the ducting must be made of sheetmetal. I believe it was brought up on here one other time, and the fiberboard had a rating of maybe 250 degrees. Having the furnace tied into the ductwork and return ducting will make it work more efficiently. One of the problems is the blowers aren't that strong, and having a 30' duct run, you will have very little air flow through the ductwork. One way to help this is have the proper backdraft dampers so the wood furnace doesn't backfeed into the central furnace. Using flex ducting is a no no with a wood furnace. In a power outage, ducting with the wood furnace can reach high temperatures. Therefore the importance of having all metal ducting and proper clearances with your ductwork. We heated with a woodfurnace just like that one for years, and they can put out alot of heat. Its when the power goes with them having a fire it can get a bit scary. I've seen water droplets sizzle off the air jacket before, not fun.


----------



## sambrent18 (Nov 30, 2010)

Thanks,
I talked to us stove earlier.  They said whatever I use it has to be rated at 750 degrees so looks like i'm putting in metal.  

Laynes, are you saying that i can't use any flex duct coming off of the main trunk line that it all has to be metal to every register, also the wood furnace will push air towards my indoor air handler so i need to put in a backdraft damper above the air handler so the furnace doesn't blow back into it, right.

Appologies for not understanding clearly, i'm just trying to make sure i have it right.   I can do the work just need to know what to do.


----------



## Gator eye (Nov 30, 2010)

Use only metal duct work and make sure you have the correct clearances on that duct work because it can get hot enough that you can't lay your hand on it, specially in the first 6 feet or so.

Spend the extra time and money and hook up that return air, it really makes a difference in how well the blower will be able to move the air in your house.

Sound like you should tell your heating and cooling guy to pound sand and find someone else to do the job or do it yourself, not really all that hard once you find a good supplier for your duct work. 

I almost hired it done then decided to take the measurements to a local heating and cooling supplier and before I knew it he had all the materials I needed loaded in my truck and the whole job took me less than a day to complete.


----------



## laynes69 (Nov 30, 2010)

sambrent18 said:
			
		

> Thanks,
> I talked to us stove earlier.  They said whatever I use it has to be rated at 750 degrees so looks like i'm putting in metal.
> 
> Laynes, are you saying that i can't use any flex duct coming off of the main trunk line that it all has to be metal to every register, also the wood furnace will push air towards my indoor air handler so i need to put in a backdraft damper above the air handler so the furnace doesn't blow back into it, right.
> ...



Yes..... Your blowers don't push much air. All of that pressure could be lost into the air handler if a backdraft damper isn't installed. Now sometimes the heat coming from the furnace is excessive, and at that point you may be able to run the air handler to push the heat through the home better. Some have and do that, but where I have the problem with it is it tempers the air. Even then if you have a steady supply of warm air it will heat much like a heat pump. Follow your clearances, get it installed properly then you can play with settings to figure what works best for you. How big is the house you are going to heat with the wood furnace?


----------



## sambrent18 (Nov 30, 2010)

The house is aproximately 2400 sq ft thats counting living space and the unfinished basement.  I have 2 vents in the basement on the other side its a garage(not big enough to pull a car in) but no vents on that side.  
The problem im running into is I can't find any suppliers in my area, yeah there around but they won't sell me anything because im not certified.  I'll check with a local metal shop and see what they can do.

Thanks


----------

