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  1. #1

    Plenum Damper - Gas Downflow w/ Wood Add-on

    I am looking for some help here. I found exactly what I need but in a different size and cannot seem to locate one. I have a one story home and upgraded the LP gas furnace last year to a 93% high efficiency downflow. In the process I fabricated a custom plenum with the idea in the future I may want to add a radiator (outdoor boiler) and A/C coil. By odd circumstance I ran across a Hot Blast wood add-on I could pickup at a decent price. I have the warm air piped into the plenum the gas furnace is sitting on and now my gas furnace is pretty much a chimney. The installation instructions state the upper compartment where the board resides is not supposed to exceed 100F. I have twin blowers on the wood add-on and it appears they will provide enough CFM to distribute a nice even level of heat in a stand alone operation. So I am looking for a backdraft damper I can install in my plenum so the wood heat does not rise up through my gas furnace and ruin the control board. I need a simple backdraft damper like what I understand to have been used in mobile home applications where the A/C system was self-contained. The plenum damper was louvered and would be normally shut, opening only by way of the gas furnace blower pressure. I have found one of these online but the dimension is only 12"x12". I need something larger. My return on my gas furnace is approximately 20"x20". Does anyone know where I can locate a plenum backdraft damper like the ones used in a downflow application where another self-contained system introduced air which you do not want to travel up through the furnace? Thanks.
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  2. #2
    I've been looking at the hotblast furnace as well and also have a gas downflow furnace installed. My plenum is in the crawl space and I'm trying to figure out how to route the dual heat stacks down to the plenum. I spoke to the manufacturer and they said that the system is not designed to be installed in a downflow system and that it will burn out the existing gas furnace. Just wondering how you accomplished your installation and did you find the damper you were looking for. Also, I was looking at your picture and it seems to me that you should be able to take 4 of those dampers and put them together and make a 20 by 20 damper. You may have to trim the ends and weld or screw them together but you would only have to lose 2 inches from each side and you would have your 20 x 20.

  3. #3

    Downflow Furnace w/ Hot Blast Wood Heat

    Hey there. Much to my dissatisfaction, not a single "expert" has chosen to reply to my inquiry. However, my installation, while not complete, has been tested, well the wood furnace fired. My furnace resides in my garage and what would technically be the trunk duct (30"x8") I suppose enters into the crawlspace via a hole where the previous owner removed a few bricks in the foundation. My gas furnace is sitting atop a custom plenum in the garage. When I state custom, I mean this monster is almost as tall as the furnace itself. I built it to potentially accommodate a radiator for an outdoor wood heater, A-coil, and a 2nd cut-in to the upstairs if needed in the future. Unfortunately, because it is 22 degrees, I am not yet running a wood/gas heat combo to see how everything works, just gas. The backdraft damper in the picture has yet to be installed, and thus, the no wood heat. I concur to a degree to what you propose in incorporating multiple backdraft dampers just like the one I have. This is the last remaining purchase and fabrication I must complete prior to transitioning to primarily wood heat. I have decided to take two of the displayed backdraft dampers and fabricate two into one larger one which restricts the gas furnace flow as least as possible. The gas furnace will undoubtedly run, although the point of wood is minimizing gas usage. However, based on increasing the free flow area, combined with the minimization of the operation of the gas furnace, I decided to move forward with that plan. All said and done, in hindsight, now knowing the complexities, expense, and test firing, the best configuration in my application probably would have been piping my wood heat into my gas furnace return plenum and wiring the wood and gas blowers together. I found the manufacturer's recommendation to keep the gas furnace blower compartment below 100 degrees, in all likelihood not to be a factor as my wood heat output temperature 36 inches away from the furnace did not exceed 130 degrees . I would have used metal duct for run to my return grill, thus allowing for a natural escape for the wood hot air in a power failure. Heat rises and would naturally want to flow some 20 feet, with a little enginneered rise, out the return rather than fall down through the gas furnace and happily underneath the house. In addition, my Hot Blast furnace draft has two dampers, the primary is electrically operated and the secondary is mechanical. Using solely the electrically operated damper would protect against overfiring the wood furnace in a power outage as it is normally open when powered, and would close during an outage. Let me know if you have any further questions.

  4. #4
    Join Date
    Nov 2004
    can we get this thread closed

    NO DIY

  5. #5

    Request to close thread

    My apologies. I thought general discussion, residential was the proper post area. God bless and Merry Christmas!

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