Wood furnace questions

[Farleyta190]

Hello all,

This is my first time posting and I am a novice at best when it comes to furnaces and HVAC. I am buying a house that has a fuel oil furnace as the primary heating source and it also has a wood furnace. Now I don't know the brand of either (I will in two days when I go back for the home inspection) but I had some basic questions which I think can still be answered.

I want to tie the wood furnace into the existing fuel oil furnace. My plan is to run the wood furnace supply into the fuel oil supply plenum to push heat through the existing duct work via the fuel oil furnace blower. I would place a back draft damper at the beginning of the wood furnace supply duct and maybe put a damper in the fuel oil supply plenum. Now won't the hot air from the wood furnace activate the blower on the fuel oil furnace if it sets of the limit switch in the supply plenum?

And I plan on keeping the thermostat set at about 55 or 60 so in case my fire goes out the fuel oils furnace can still kick on and supply heat to my house. I will tie the return duct work from the fuel oil furnace into the wood furnace. That is my plan. Each furnace has it's own chimney as well and all duct work is metal and I'm pretty sure all clearance requirements can be met. . Any thoughts, suggestions or problems with this plan. please share. Thanks

 

[begreen]

Welcome. I am moving this over to the boiler room for a more targeted response from other furnace owners. This question is getting asked more frequently recently. It is not recommended to use the main furnace blower for the wood furnace. You might consider buying a good combination fuel furnace if this is the desired plan.

What furnaces are you considering?

 

[Farleyta190]

I'm not sure the make of either furnace, I'm still in the early stages of buying this home. But the home inspection is Tuesday so I'll be sure to get the make and model of each. The wood furnace is only about 10 feet from the existing furnace and start of the duct work. If the wood furnace had a powerful enough blower could I just tap in and share the duct work of the existing furnace, and just put a damper in to ensure the wood furnace didn't blow back into the fuel oil furnace?

In case anyone is wondering, the furnaces are located in an unfinished basement, the house is two stories and about 1700 square feet.

 

[laynes69]

Your central furnace's fan control can be activated from the heat of the woodfurnace. Depending on where the fan control is located, you could place a damper above the central furnace's fan control. You also want to be careful with backdraft dampers over a woodfurnace. If it has a plenum, you want it to remain open unless it's out or not being used. You don't want it to be closed when operating, in case of an outage. If you were looking to replace the furnace and wanted a single blower with no dampers in the system, then you would install in series which utilizes the central furnace's blower.

 

[begreen]

I seem to recall some furnace manufacturers specifically saying that series installation is not permitted with their furnaces. That's why I asked what model furnace.

 

[Farleyta190]

Yes the plan would be for the wood furnace supply damper to be open unless the fire dies out or the furnace isn't being used. Won't the damper stay open unless air flow from the opposite direction closes it, like when the fuel oil furnace kicks on for back up?

Begreen I'll be sure to check to see if that's the case for each furnace.

Second question to laynes69. If I put the damper above the fan control in the fuel oil furnace will the hot air from the wood furnace be able to reach it in order to activate the blower?

 

[DoubleB]

I might have missed it...what problem are you trying to solve? What's wrong with the way the furnaces are currently arranged?

 

[Farleyta190]

Double 8

The wood furnace is not hooked up to any duct work. I wanted to use wood as my primary fuel source and keep the fuel oil as back up and use the existing duct work and fuel oil furnace blower to move the hot air from the wood furnace. Just looking for tips and the correct way to do a project like this and/or if it's feasible at all

 

[laynes69]

The damper in the fuel oil furnace would prevent backflow where the limit control would be activated. Once you get the model of the furnace, post here and we will get it figured out.

Begreen is right about series. I was just stating if you wanted to go this route, there are furnaces that allow this, but without knowing the model... Otherwise, you'll be looking at a parallel install.

 

[Farleyta190]

Ok I'll post the models of each on Tuesday and get some more info on them. Can someone explain the difference between series and parallel?

 

[begreen]

This is for the Drolet Tundra. Series is one furnace feeding into the other. Note that series is not permitted. (click to enlarge)

 

[TheBigIron]

begreen,

With that parallel Drolet install would you need a damper on the return side of the wood furnace to prevent condensed air being sucked through the wood furnace in the summer time??