"Make-Up Air"

egclassic Posted By egclassic, Dec 8, 2011 at 9:20 PM

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  1. egclassic

    Feeling the Heat

    Jan 1, 2011
    SW Ohio
    Thats exactly my concern here!
  2. Ehouse

    Minister of Fire

    Jul 22, 2011
    Upstate NY
    Try this: open the ash hatch, open the cellar clean out, put one of your incense sticks at the edge of the ash hatch and see where the smoke goes in different situations: with no fire in the stove, in mid burn, and at the end of a burn when the draw up the chimney is presumably low. I'm guessing that at the end of a burn, the flow may reverse as the cold air drops into the basement. If the ash hatch has been open all this time it may be contributing to your draft problem. The chimney may be pulling air up, the ash channel may be pulling air down at the same time. Try shutting the ash hatch and see if that helps.

  3. LLigetfa

    Minister of Fire

    Nov 9, 2008
    NW Ontario
    In my opinion, there are two separate issues that relate directly to this thread, 1. Convection forces internal to the home, and 2. Air infiltration/exfiltration through the building envelope.

    When you have a strong point source of heat, you will also have strong convection currents within the home which cause cold drafts. When there is also air infiltration through the building envelope, the drafts are intensified. The strong point source of heat can also intensify the exfiltration of hot air through the building envelope. This causes the neutral pressure plane (NPP) to rise which in turn increases the cold air infiltration.

    The building air system needs to be balanced factoring all of the aforementioned forces. Points of exfiltration need to be reduced to lower the NPP and not just the points of infiltration sealed which raises the NPP. There will be points of exfiltration that cannot be prevented. Exhaust fans, flues, clother dryers, etc. all consume indoor air so makeup air must be provided. If you only seal up points of infiltration and don't provide adequate makeup air, you risk radon gas infiltration and/or flue reversal and potential carbon monoxide poisioning. The building needs makeup air which should be provided in a controlled manner that does not create cold drafts. Once the points of exfiltration are taken care of and makeup air provided, you can move on to the other issue, that being strong convection currents.

    The way to deal with convection currents is to work with it and increase the currents so as even out the high and the low. The lower the high and the higher the low, the weaker the current and the less the discomfort. Ceiling, through-the-wall, doorway, and duct fans perhaps used in combination will do that.

    I designed my home with wood heat and the natural convection currents in mind. The main floor is open concept, the crawlspace is conditioned space, and part of the upstairs is heated by reclaimed heat from the chimney chase. The stairwell allows warm air to rise and cold air to fall. I have one large 650 CFM duct fan drawing cold air off the crawlspace floor and blowing it up to my stove. The hot air from the stove blows across the floor and rises. Air is drawn down into the crawlspace via the hatch under the stairs which is some distance from the stove and warms the floor. Makeup air for the whole house is via a HRV that dumps into the cold air return of the furnace duct. The path of least resistance for this makeup air is a cold return register in the hall near the front entry where the dog enjoys the coolness when she is in. She doesn't like the heat and prefers to be outdoors most of the time.

    I understand that retrofitting an existing home to wood heat may be more challenging and in the end, you might be better off to use a space heater in the cold room if moving the air wiith fans proves impractical.
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