Welcome! Here are the website rules, as well as some tips for using this forum.
Need to contact us? Visit https://heatinghelp.com/contact-us/.
Click here to Find a Contractor in your area.

Wood Furnace connected to traditional furnace

Options
GW
GW Member Posts: 4,743
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
Gary Wilson
Wilson Services, Inc
Northampton, MA
gary@wilsonph.com

Comments

  • hot_rod
    hot_rod Member Posts: 22,505
    Options
    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 :)
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • GW
    GW Member Posts: 4,743
    Options
    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!
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • hot_rod
    hot_rod Member Posts: 22,505
    Options
    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
    Bob "hot rod" Rohr
    trainer for Caleffi NA
    Living the hydronic dream
  • GW
    GW Member Posts: 4,743
    Options
    yes i see what you mean, that sure would make it easier.
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • Ironman
    Ironman Member Posts: 7,400
    Options
    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!
    Bob Boan
    You can choose to do what you want, but you cannot choose the consequences.
  • GW
    GW Member Posts: 4,743
    Options
    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.
    Gary Wilson
    Wilson Services, Inc
    Northampton, MA
    gary@wilsonph.com
  • Tim McElwain
    Tim McElwain Member Posts: 4,629
    Options
    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
    RobG Member Posts: 1,850
    Options
    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.