Add-on Wood Furnace installation

[Fixedblade]

Greeting all: I'm trying to install a used Royall add-on wood furnace and can't decide if I should do it in series to my existing oil hot air or completely separate. Both are installed in a room adjacent to my garage. My oil hot air furnace is a simple set-up with just one register dumping all the hot air into the kitchen area of my home and it diffuses very well thoughout the house. The wood furnace was used as an add-on and has no distribution blower of its own. The only way I can install it in series is to have the oil furnace pull the already hot air from the wood furnace into its plenum and use its blower. I'd also duct the cold air return into the house separately. I've been told installing it that way is a no-no as the oil furnace shouldn't be fed hot air into its cold air return as it can damage the blower motor/belt. Others have told me it's often done with no problems. They did suggest taking the filter out of the oil furnace first and installing it elsewhere so the hot air won't be going thru it. The other alternative is to get a separate distribution blower and filter box to install on the wood furnace and duct it in separately to the house creating a separate system. My real question is about whether sending hot air from the wood furnace into the oil furnace will be a problem or hazard. Thoughts anyone???

Thanks, FB in Vt.

 

[pybyr]

Hi fellow VT-er ! Where in the NEK are you located?

You definitely do not want to send the heat from the wood furnace through a compartment that contains the oil burner's blower motor. Nearly all furnace blower motors rely on the movement of the air for cooling, and that just plain won't happen if you're feeding hot air into the unit. Most electric motors (outside of special applications) are not rated for ambient temperatures of the sort that you'd be feeding from the outlet of a wood furnace. You _might_ be able to find a severe-duty motor that you could swap in, but it may be expensive.

Parallel rather than series may be a good idea anyway-- that way, when you run oil, you won't be trying to heat up the wood unit's mass of metal on the warm air's way through.

You may be able to get a free blower for the asking if you know of anyone who works on furnaces-- the blowers usually outlive the rest of the furnace. Heck, if you come up short, I think I even know of a place I could come up with one for you.

 

[laynes69]

I reinstalled a woodfurnace dad heated here for 20 years from a parallel install, to a series install. You need the oil furnace first, then duct into the wood furnace. It made a night and day difference. But you should have a bypass, so in case you didn't burn wood you don't have to heat that mass like mentioned. I now have a new furnace thats installed in parallel with the LP, but a series install is very simple and effective. If going series just make sure the oil furnace is operating fine. Otherwise you lose your blower, or the furnace fails to fire and you have no way to push the heat out the woodfurnace. If going parallel then you need backdraft damper and such. Also Central air if you have it will play in effect on how its ducted.

 

[Fixedblade]

[quote author="pybyr" date="1264814215"]Hi fellow VT-er ! Where in the NEK are you located?

I'm in Derby, heart of the NEK and about 30 below zero wind chill today. Got the big pellet stove and oil furnace pumping full speed to heat my 3000 square feet of 200 year old house... Looking forward to having the wood furnace to use instead of the oil as we all know it's just a matter of time before that stuff goes WAY up again...

FB

 

[pybyr]

Hi fellow VT-er ! Where in the NEK are you located?

I'm in Derby, heart of the NEK and about 30 below zero wind chill today. Got the big pellet stove and oil furnace pumping full speed to heat my 3000 square feet of 200 year old house... Looking forward to having the wood furnace to use instead of the oil as we all know it's just a matter of time before that stuff goes WAY up again...

FB

I know Derby- great area; I used to work a few days a week in Newport a long time ago.

I used to have a Sam Daniels wood furnace in series with my oil furnace-- the oil came first, and its blower sent the air through the wood unit (with the blower only activated) when using the wood unit. Worked reliably, but my gasifier is night and day better at heating my own big ol' VT house without resorting to oil.

 

[pybyr]

If going series just make sure the oil furnace is operating fine. Otherwise you lose your blower, or the furnace fails to fire and you have no way to push the heat out the woodfurnace. .

It's possible to run the blower's control in parallel to the wood unit so that the blower will come on even if the "oil gun" is not in operation- my old system used to be set up that way.

 

[laynes69]

Right, so did mine. The relay on the circuit board would allow for blower only operation but when there was a call for heat the LP furnace would fire. With the safetys in furnaces, if they don't fire 3 times they shut down disabling the blower. Sounds like mine was setup the same way. There was only 2 wires going from the woodfurnace to the LP furnace board. We had our unit get hot one night, because the woodfurnace didn't keep up and the LP furnace failed to fire disabling the furnace. I smelled it and had to reset the furnace to get the blower back.