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Maintaining temps with wood furnace?

Post in 'The Boiler Room - Wood Boilers and Furnaces' started by baskinglizards, Nov 5, 2007.

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  1. baskinglizards

    baskinglizards New Member

    Joined:
    Sep 12, 2007
    Messages:
    27
    Loc:
    Northern Vermont
    Hi everyone,

    We are fairly new to woodburning as a source of home heat and need some advice from you experienced woodburners out there. :)

    We are currently using a combination wood/oil furnace and it is a forced hot air system. So far, we have no difficulty starting a fire and maintaining a hot fire. What we are wondering is if it's possible to maintain a fairly constant temperature. We find that the temps in our house go up fairly quickly when we run the wood furnace, and that they continually rise despite our efforts to simply maintain temps. We're not sure if it's because we're not burning the wood properly, or if it's because the furnace is very old, warped and inefficient, and probably lets in more air than it should, or if the furnace is just too large for our needs.

    Basically, when we start the fire, we place the kindling and logs in a criss-cross pattern and we have the damper fully open to encourage air flow and get a hot fire going, and once we have a good bed of embers in the firebox, we load it with several large logs in a compact pattern and shut the damper to encourage a slower combustion, but we still seem to get a lot of heat from the furnace. When we load it with, say, 5 logs that are about 8-10" in diameter and 18" long, we get about 4 hours' worth of heat. Does this sound about right?

    Thanks for any help!

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  2. Nofossil

    Nofossil Moderator Emeritus

    Joined:
    Oct 4, 2007
    Messages:
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    Loc:
    Addison County, Vermont
    Sounds like you have an older unit that doesn't have any thermostatic controls. Trying to maintain constant heat by hand is difficult at best. Many systems have a draft damper that's controlled by a house thermostat so that the fire is controlled by how much heat the house needs.

    Years ago, I had a hot-air furnace that sounds similar to yours. Eventually I was able to learn its ways well enough to get by. Your theory about air leaks might have something to it. Is there any way to seal it up so that you can control the air inlets more completely?
  3. baskinglizards

    baskinglizards New Member

    Joined:
    Sep 12, 2007
    Messages:
    27
    Loc:
    Northern Vermont
    I think it does have thermostatic controls, actually. The blowers that force the air through the ducts come on automatically when the air inside the plenum reaches a certain temperature. Also, there is a draft fan located in front of the firebox that I suspect should be wired to the thermostat, but it isn't. We haven't bothered trying to re-wire it, because we were under the impression that the only reason you would use a forced draft is to get the fire to burn hotter, and our problem is that it puts out too much heat.

    We replaced the fiberglass gasket around the firebox door, but it is so badly warped that we really can't seal every single crack. Also, the door for the ashpan doesn't close properly. There really isn't any way to fix it other than just replacing the doors and given how old the unit is, we don't want to invest any money into it. We also suspect that the unit really isn't designed to burn wood that efficiently, since it also burns oil - the oil-burning chamber is basically part of the wood-burning firebox, so that is probably letting air in, too.

    So do you figure with a newer, more efficient furnace, that we will in fact be able to control the temperature output better? How often should you have to tend to the fire to do that? My husband is under the impression that burning wood means dealing with cyclic temperatures, but I tend to think otherwise, especially with the newer furnaces out there. Or maybe I'm wrong. LOL
  4. Nofossil

    Nofossil Moderator Emeritus

    Joined:
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    Messages:
    3,419
    Loc:
    Addison County, Vermont
    I'll let others chime in, but I think any newer furnace will be thermostatically controlled. If you're getting too much heat even without the fan, I think that air leaks are doing you in. Newer units are likely much more efficient as well. Good luck....
  5. baskinglizards

    baskinglizards New Member

    Joined:
    Sep 12, 2007
    Messages:
    27
    Loc:
    Northern Vermont
    Thanks for all your feedback. We figured most of it was the unit itself, but we're still learning a lot about woodburning, too, which we will probably have to re-learn when we get the new more efficient furnace. LOL As in - how to arrange the logs for a slow burn and a clean burn, etc. Even with our old inefficient furnace, though, it's still better than heating with oil until we get the new furnace. :)
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