US stove Hot balst Ducting?

[NYRICH]

Hi, new to the site. Great info man i didnt think as many people were into heating with alternative sources. Well I say to hell with Exxon Mobil!!
Anyhow got a new US stove hotblast add on furnace. Got the chimney installed. RAnch house 1 story . The Add on is in the basement next to my Propane forced air unit. Im not a sheet metal expert so i need some help here. The furnace shows multiple connection ideas for duct work. It also states you should not direct the hot air from add on into the cold air return of the gas furnace. I had a HVAc guy here who told me he has done it on numerous installs. He said they key is to hit the cold air return farther down the line. That way the air is not to hot for the gas furnace blower. The returns from the house will add with the warm air from the wood furnace? It seems to make sense because otherwise the blower on the gas furnace seems like it would compete with the blowers on the wood furnace. I thought about piping in on the updraft plenum of the hot air out on the gas furnace. But how can you honestly get both blowers to work in cunjunction? Semms like they would push at each other. I also have an Ac a coil in there. So i need to get above it. I know that when summer comes i need either dampers or blast gates in the 8" duct to stop my ac from filling the woodstove. What has anyone out there tried and what works best? P.S> my heating trunk in my home is also DUCT Board. Not sheet metal. Anyone know the temp rating on Duct Board.
Thanks
Rich WNY

 

[laynes69]

With the high temps that are possible with the wood furnace, Do not run the heat into the cold air return. On the supply from the wood furnace, with a parallel install into the plenum, you will need to add some sort of damper under the 2 ducts to keep the heat from backfeeding into the main furnace. Also just use 2 8" dampers to aid for shutoffs in the summer. I can't answer your question about the heat ratings of ductboard. I can tell you with galvanized ductwork, clearances become important in case of a power outage. You don't want the ducts touching the combustibles up ahead. You may find that you won't need the main furnaces blower to help push the heat. But there are ways to do it if needed. Whats the square footage of your home you are going to heat? Good luck, hope this helps!

 

[Duetech]

Hi NYRICH,
I had a Hot Blast for a time and went to an Englander. I have metal duct so I can't help with the duct board other than it should be UL rated so any heating installation/repair company or maybe building supplies store would be able to give you the answer you need.

laynes69 is right about the cold air return. Those wood furnaces put out some serious btu's and the cold air return is designed for cold air return. The limit switch in the furnace will kick in your furnace blower if the temperature gets too high and then you would be cycling some pretty hot air over your furnace air filter and blower motor. That could stress the temperature design limits of the blower motor because it would not get air cool enough to keep it from over heating under load. I had to put a damper that restricted flow into my heat exchanger area on my oil furnace or the blower on the oil furnace kept kicking in and I was plumbed into my hot air plenum. The damper was designed like the draft damper on the oil furnace exhaust in that it had an extended over center weight that would rotate the plenum damper closed when the blower from the wood furnace kicked in. The Englander came with one heat run outlet but it supplied the back draft damper for when the oil furnace kicked in. If both blowers kick in at the same time they will resist each other but in my experience neither will over power the other but they will act as combined output and boost the duct pressure and really force some air out of your ducts...Stay warm...Cave2k

 

[Pyromaniac]

NY RICH, I've got to be honest with you... I have the set up that your heating contractor has suggested and it works great, BUT ITS NOT DONE RIGHT. I've only had this set up( a hotblast 1557 connected to the cold air return) for the end of last winter and the beginning of this one but I cannot sleep comfortably knowing its set up this way. Like you I had a heating contractor do it this way saying he's done it this way numerous times with no problem.

The problem for me is the manufacturer clearly states NOT to do it this way so if your house burns down do you think the insurance company is going to cover you? I don't think so either. I don't burn my furnace near as hot as I could (or should for that matter) as I try to find the perfect balance between a nice flue temp but not too hot to overheat my central furnace blower wiring and a/c coil wiring/switches too. I've even had another contractor suggest I could be evaporating my a/c heatpump coolant by running it this way, too. Don't make the same mistake I have... Do it right the first time!

I believe your better off researching the way laynes69 has his even if it takes longer and more cash in the front end. I'm basically going to be redoing mine the right way myself AFTER I paid someone else to do it wrong. What I've found is that most heating contractors in my area don't know the first thing about heating with wood.

 

[Gator eye]

I have a Yukon wood furnace and I would not hook my hot air into the cold air return. My duct work gets hot to the touch when the stove is really crackin, even fifteen, twenty feet down the line. I ve never taken a temp reading but I wouldn't want to lie awake on a cold night worrying about it.

I am hooked into the gas furnace plentum on top of the A/C condensor. I have a one way check valve to keep the gas furnace from blowing into the wood furnace but nothing to go inbetween the wood to the gas furnace. I don't seem to have a problem with back feeding air through the gas furnace into the cold air return.


And...don't skimp on hooking up the cold air return to your wood furnace, it makes a huge difference in the operation of the wood furnace.

 

[smokinj]

you dont want to go throug the cold air of your propane furance and i belive all duct work sould be metal

 

[matt701]

A few years ago when I first installed my hotblast with the factory blowers and only 2-8" ducts, I also hooked mine to the return duct. I knew it got really hot and I wanted to know how hot. I put a plastic/glass thermometer on top of both big return ducts upstairs. I could smell burning/melting plastic soon after. It shriveled up the thermometers and broke the glass out of them both, one being about 20 ft down from the wood furnace. After that, I put a much bigger blower on the furnace to keep the temps down which helped and now have it hooked up the correct way with with proper clearances. The original blowers don't move much air, so the temperature of the air coming out could be a real hazard, especially if you have much resistance from the ducts reducing the airflow even more.

 

[ikessky]

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Here's how I ran my Daka add-on furnace. Due to the size of my A-coil, I couldn't fit the 8" duct's into the plenum. I am tied directly into the duct work, but only about 1/2" away from the plenum. The wood furnace's blower comes on when the air jacket reaches 110 and goes off when it gets below 90. I find that this constant air movement seems to heat my house fairly well, but we did take a few of the storm windows off so that we can heat the outside a little if necessary! I have not yet installed back-draft dampers, but have only had the gas furnace fan kick on twice. It did make some funny noises in the sheet metal of the wood furnace, but I doubt it caused any damage.