Wood Furnace connected to traditional furnace

GW

I have little experience with wood furnaces being parked next to regular furnaces. I looked at this one job where there are the basic manual dampers on both sup and ret connecting the two appliances. The person wants to update their furnace, keeping the wood furnace. Are there some basics that need to be obeyed- in other words, what keeps the gas/oil furnace from simply cycling its energy through the wood appliance? Or, is it better to tip my hat and let some other person do this type of install?

Thanks, Gary

hot_rod

I would think the same logic applies to air handlers as hydronic boilers. You would never want the gas furnace flowing through the wood fired one.

I've also been told the wood fired ones can run very hot, possibly causing concern with limit switches in the gas fired equipment.

In hydronics a simple 3 way valve or a few pumps with hydro separation solves that. With ducting, it seems some sort of full sized dampers would be needed to get 100% separation between them??
Depending on manual operation of that damper would concern me. Wonder if the manufacturer of the gas furnace would void warranty if they knew of this "cross connection"

Do you like to gamble

GW

Thanks HR, no I don't like to gamble for such small numbers such as this. When i roll the dice there are bigger carrots at the end.

The trouble is the gas furnace sends air to the house, the wood sends heated air into the gas furnace (well, it's an oil furnace now), your 3-way mix valve analogy is a bit different.

I'll just walk, unless someone chimes in. The trouble is the people are new to the home, and of course the prev people said 'it works great'. So, and lack of greatness becomes my problem, not worth the risk!

hot_rod

Wise decision. Wood heat in a boiler or furnace requires a lot of interaction from the homeowner. A steep learning curve is sometimes involved and not all homeowners get the hang of adjusting the burn to the load conditions.

I was referring to a 3 way diverting valve in my example. I'm not sure such a device exists for ducting? A flapper that only allows flow through one device at a time

GW

yes i see what you mean, that sure would make it easier.

Ironman

I do a lot of outdoor wood boiler installs and the beauty of hot water heat is that it can easily be integrated with almost any other type of system. I'm sure you know that. However, mixing a wood burning hot air furnace with a gas furnace is another animal altogether.

I suppose that you could construct a damper setup using a modutrol motor that would have one damper n/c and the other n/o. That would prevent mis-orientation of the dampers, but it would be somewhat costly. I shutter at the thought of manual dampers and a gas furnace with an ECM motor. If the H.O. gets them wrong, a very expensive motor is gonna be toast!

GW

yes thanks Bob. The fact that this guy is new to the home (new to the system) makes it tricky; his inability to master the system will become by problem.

Tim McElwain

The first concern I have as to code is how are they vented? We have in the past had equipment that could burn wood or could run on gas (never at the same time). Most of the ones I saw were boilers not furnaces so the heat transfer through piping was not a problem.

RobG

You could always call the wood furnace manufacturer. I'm sure that you are not the first person to have this question. Let us know if you get a answer.