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  1. #1

    woodstove change fan location

    Howdy gents,

    Long time listener first time caller. I've searched through your forums somewhat and haven't really found the answer i'm looking for. Forgive me if this was already asked. A little background first.

    I burn quite a bit of wood in the winter, generally about 4 cords a year. Pretty much use it for a primary heatsource, sweep the chimney a couple of times a year since I choke off the box at night. Usually the heater will kick on about 5am and run for a bit until I restart the fire, this has saved me a bunch of money on propane. I also frequently check my smoke and carbon monoxide detectors too. So... that should cover basic safety questions.

    On to my setup and question.

    I have a woodstove insert with a heat exchanger and a pair of 3-speed 200cfm fans. The insert is roughly 20 years old made by Long Manufacturing (since out of business) and came with house. I've happily used this system for the last 8 years but one of the motors went out. These things are $150 a pop and I'm afraid the other one is one it's way out too. Instead of dropping 300 clams, why not add some ducting under the hearth down through my crawlspace and tap into the hvac return? I would love to be able to reduce the fan noise in the room also. I imagine I would need a gate at the tap so when the heater is on, the return is not getting air from the fireplace duct.

    Anyway, just wanting a few experts to chime in and test the validity of this idea.

    thanks!

  2. #2
    Join Date
    Jan 2006
    Location
    Powell River, BC, Canada
    Posts
    763
    Generally, creating a negative pressure area close to a naturally drafting fire is a good way to wake up dead. Put air INTO the space, and have the return at the other end of the house to draw the warmer air through. How are you currently supplying combustion air to the unit?
    Where are you? Are you done yet? I got ONE more call for you.....

  3. #3
    Thanks for the reply. Hopefully this picture and a little more detail will make my question more accurate. Currently with the stock fans the air is pulled from the sides and pushed out the top of the stove. FWIW: the chimney is nearly 30 feet long and creates one heck of a draft.

    So back to my question:

    The intake for the return hvac line is in another room. I was hoping to tap into that and push the air into the heat exchanger of the wood stove. Not reversing the airflow, but in a sense moving the fans from the stove into the crawlspace of the house. As you can see in the picture, the hot air will be circulated around the firebox and out the front, this should not create a negative pressure should it? The duct work will be hidden inside the bottom of the hearth and come straight up where the current fans sit. The only thing visible is the small gap under very bottom of the stove, shouldn't be too hard to make it blend in.

    Feel free to rip my idea to shreds, I want it to be safe!

    thanks again.
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  4. #4
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,294

    Cool

    No way Jose. this stove is not tested or listed for that application. You would also screw up your furnace. Just let the woodstove pump heated air into the room then use the return duct to capture it.

    I hope that stove has an insulated listed liner. If not, pull it and replace it with one that does and is listed. If not lined with a properly sized listed liner, it is a fire hazard or what we lovingly call a "slammer"

  5. #5
    Quote Originally Posted by hearthman View Post
    I hope that stove has an insulated listed liner. If not, pull it and replace it with one that does and is listed. If not lined with a properly sized listed liner, it is a fire hazard or what we lovingly call a "slammer"
    It was when I purchased the house but upon first sweep and inspection they told me about "slammers". It now has a properly sized liner.


    You would also screw up your furnace
    Not that I don't believe you, but could you give me more detail?


    thanks for the replies.

  6. #6
    Join Date
    Aug 2004
    Location
    S.E. Pa
    Posts
    6,294

    Cool

    If you do major surgery (spelled-costing more than $300), and install ducts to and from the existing furnace, you screw up the airflow and heat transfer of the furnace. you can cause all sorts of problems from burning out the blower to damaging the heat exchanger and vent or even causing carbon monoxide formation by improper heat transfer. You see, if the air returning to your furnace is already hot, it cannot pick up much more heat from the furnace burners. That excess heat can actually cause a fire as the furnace does have a top end temp, rating.

    Now, if you intend on just using the furnace blower and ducts when the furnace is not firing, you still have screwed up the ducts. The static pressure will probably be so jacked you won't get much airflow, which can harm your blower. Moreover, when you do go back to using the furnace, you would have to have some sort of duct dampers so the fireplace loop did not tie in. this would undoubtedly lead to some intereference with airflow in the ducts.

    Lastly, this stove is not listed for connection to ductwork. By hacking a hole in it, you void any listing (UL1482) it might have been tested to. That makes it against the code, hence illegal. Should you go forward with this abortion and had a fire, your insurance company could probably deny the claim.

    If this was such a great deal, why hasn't anyone done it before? Its because they did and the fires and problems it caused outweighed the little gains.

    You can extend your supply into this room IF your HVAC tech says its ok without screwing up the airflow to the furnace and it is not within 10 lineal feet of the fireplace opening. However, doing so could cause the stove to spill smoke and carbon monoxide into the home.

    Is your CO alarm listed as in off the shelf or a special unlisted low level model? Oh, yeah, chopping a fireplace apart would also violate the code on fireplace construction. There is no provision in the code for ducts in fireplaces btw.

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