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Outside Combustion Air?

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by velvetfoot, Dec 17, 2005.

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  1. velvetfoot

    velvetfoot Minister of Fire

    Joined:
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    Loc:
    Sand Lake, NY
    Yea or Nea? My current insert did not come with one and works great. The current place's central hot air gas furnace gets its air and exhausts combustion products through the wall so there is no suction on the house envelope. The new house has a zero clearance fireplace that I would like to insert-ize. However, the new place also has a boiler that gets its air from inside the house. Alas, it also has a slight radon problem that will likely require a sub-slab depressurization system, that might also take some (maybe not much) air from within the house envelope. Negative pressure in the house (without the fan) would not help the radon problem since it would be sucked into the house.

    So...... should I get an insert with an outside air supply? I've read somewhere on the web, I believe, where they are controversial. I spoke with a local furnace supplier about an outside air supply for the boiler (oil) and he says they don't work too well because the burner cannot change settings as with the changing air temps (and hence, density) of the incoming combustion air.

    The current zero-clearance fireplace has an outside air intake. The house is two years old.

    Thanks

    (sorry if this was covered somewhere on the forums)

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  2. elkimmeg

    elkimmeg Guest

    A former poster gave the best description of outside air (Downeast)
    It was his contention that outside air was a pressure relief valve more than a combustion source.
    He also brought a very valid point about the feed system and its relationship to wind direction .
    It is possible, that the wind can hit a house on one side and leave a vacum on the otherside. and that having one outside outlet
    many times created a vacume instead of a supply. He suggested multiple outlets to eleviate this situation
  3. elkimmeg

    elkimmeg Guest

    code wise outside air may be required to produce the proper amount of combustion air vollume for all fuel burning appliances, if enough vollume is not pressent to satisfy the demand. There is also the location to factor proximity of two fuel burning appliances in close proximity doesnot lend itself to either running and drafting correctly. If not enought combustion air available, one appliance can pull exhaust air from the others' chimney into the living space. The formular is for every 1000 BTus the appliance outputs 50 cubic ft of free flowing combustion air is required. By free flowing is meant, no openings to adjacent additional air spaces shall have a closable door

    Why do wood stoves draft poorly in the cellar? A combination of reasons all add up to a less that desirable results. One the central burner is usually located there, posibly a fuel fired hot water tank and many times a clothes dryer. All which exhaust air. (Result insufficient combustion air) Two the wood stove is located at the lowest level Not the ideal location. Third most chimneys are located on and outside wall. They never maintain enough heat to promote proper draft
  4. velvetfoot

    velvetfoot Minister of Fire

    Joined:
    Dec 5, 2005
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    6,967
    Loc:
    Sand Lake, NY
    Thanks for response. Good points. It seems that in some communities actually require outside air for wood-burning appliances, but in reality, they may not perform that well?
  5. joeiii

    joeiii New Member

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    Dec 18, 2005
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    9
    Taking this post in a slightly different direction, my home is 200 plus years old. I am installing a pellet insert in the fireplace which is cental to the house. The installation instructions suggest an air intake that will draw from the flue. I have installed a 25 foot SS exhaust flex liner that ends with a with cap at the top of the chimey. They also show a plate installed where the damper is to block off natural draft.

    My questions are.... why have a plate damper down low if the cap up top is sealed?

    If I intake air from above the plate, and the cap is sealed up top, won't this be creating negative pressure as well and effect efficiency?

    thanx

    joe
  6. joeiii

    joeiii New Member

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    Sorry Velvet, didn't mean to jack your thread. I read about inserts & outside air and figured I was in the right post. I'll try and find another post that deals with getting outside air to a central chimney home.
  7. richg

    richg Minister of Fire

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    Nov 20, 2005
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    888
    I installed a new roof, Andersen windows and doors, had vinyl siding installed, and the house was tight as a drum. Too tight, it turns out, to operate a pellet stove correctly. Added an outside air connection, and the problem was solved.
  8. joeiii

    joeiii New Member

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    Dec 18, 2005
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    As I sit and reread the St. Croix manual, I see that the outside air inlet goes only as far as the damper. However.... I did notice this time that the storm collar up top is recommended to be vented. I haven't sealed the top yet and wonder if a half inch riser on the cap be appropriate to allow enough fresh air in?
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