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  1. #1

    Invented - new controlled fireplace air intake vent

    Necessity is the mother of invention, and so it goes.

    I needed a controlled fireplace air intake vent, in order to seal the fireplace doors of my wood burning open through fireplace. So I invented one.

    The research called for 2-3 times the air flow provided by the then code 4" round air intake, to sustain a moderate fire. The research also warned of backdraft, requiring backdraft protection so that combustion products do not exhaust out the air intake during a wind event. Further, the research warned of coupling between flue and air intake which could accelerate air flow and burn rate, suggesting that intake air flow be controlled if the doors are sealed.

    The researched warned that firebox temperature can rise when the doors are sealed, due to a reduction in quenching air from the house. Thus it is important to increase the air intake size to provide more quenching air. This is accomplished by directing the air up from vents parallel to and along the bottom of the doors, and not directed at the fire.

    The doors are tempered glass and 11" from the fire grate on either side in my case. I have 14" vent slots in front of the doors on either side. The doors are tempered glass which loses it's temper at 500 F. The current hottest temperature reading on the glass is 210 F. Typical is about 180 F.

    The closer the glass is to the fire the hotter it gets. So, you have to be careful with this sort of thing. Some fireplaces have the fire much closer to the glass.

    With my current arrangement I have a hole in the wall that is 12.56 square inches that never closes, and is a heat loss from my house. In addtion, the damper does not seal air tight and leaks air out the chimney constantly. By sealing the air intake and the doors, I can significantly reduce my heat loss through leakage.

    So, to seal the doors I needed to meet the requirements outlined in the research.

    I have invented an outside hooded vent with remote controlled flap that provides a weather stripped lock closed position, infinitley variable flap openning for intake air control, and instant weatherstrip sealed flap closure on backdraft.

    The remote control uses bicycle cable jacket and cable, with a control lever mounted on the wall next to the fireplace. The air supply can be completely cut off by closing the flap. This could be handy for chimney fires or if you just want to turn the fire off, but is most important for shutting the hole in the wall when the fireplace is not used.

    The ducting is 3 1/4" x 10" rectangular duct, which provides 2.7 times the cross-section area for air flow compared to the standard four inch round air intake.

    I am installing this in my own home. Does anyone think there could be a market for this sort of thing?

    Even if you don't seal the doors, closing the air intake is a major heat loss savings, and providing more air to the firebox from outside reduces the amount drawn from inside. It provides backdraft protection. It still seems like a good idea.

    I just don't know if there is much of a market for such a thing. Do people still put in wood burning fireplaces or has everyone gone gas, woodstove, and inserts.
    Last edited by foaf; 11-17-2010 at 03:20 PM.

  2. #2
    It's a bit rough in finish, but is fully functional and solid as a one off for my fireplace. The flap is spring loaded to provide the air flow with a spring assist to lift the flap. The big dip in the edge is a compensation for the spring warping the flap, which could be easily fixed in a production design.

    The spring assist decreases as the spring relaxes, but as the flap rises from horizontal more of the flap weight is transferred to the hinge reducing the weight the air flow must lift to open the flap further, and so compensating for loss of spring tension.

    Reverse air flow slams the flap shut, to provide complete sealed backdraft prevention.
    Attached Images Attached Images     
    Last edited by foaf; 11-17-2010 at 04:24 PM.

  3. #3
    Quote Originally Posted by foaf View Post
    The spring assist decreases as the spring relaxes, but as the flap rises from horizontal more of the flap weight is transferred to the hinge reducing the weight the air flow must lift to open the flap further, and so compensating for loss of spring tension.
    I just wanted to add that between the spring tension and the weight transfer, the flap remains more or less weightless throughout its range of motion, and the air does not struggle to lift the flap from horizontal, reducing any bottleneck that can be caused by the flap.

    I just need to pick up some longer cable jacket and cable to install the thing.

    Cheers

  4. #4
    One more thing.

    I mentioned research. This is the best I could find.

    http://heatkit.com/docs/airreq.PDF

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