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  1. #1
    Join Date
    Oct 2005
    Posts
    3
    I need to increase the ventilation in my home and am considering using a fan cycler. This brings in fresh air, but does not exhaust stale air. I can adjust it to bring in the required amount throughout the day. Will I run into problem with excessive pressure and/or humidity that may lead to moisture problems developing in wall cavities? I am located in Illlinois (~6,000 annual HDD). Thank, Neal

  2. #2
    Join Date
    Jun 2004
    Location
    4H: Hot, Humid Houston H.O.
    Posts
    3,304
    From what I have tried to learn, your concern is quite a valid one. Theory says you will get positive pressurization, and with air going outward thru who-knows-what cracks in the walls, it would seem probable that air would meet some object lower than its dewpoint temperature.

    I don't know how it would fit into your possible plans, but an exhaust fan strategy would avoid that problem. You might have a small bathroom fan running continuously, for example.

    Have you been able to research what Joe Lstiburek or his company Building Sciences Corp. would say about your situation? I do believe you could phone them and you might be able to get steered toward a good answer -- a book recommendation possibly. Lstiburek has a "Builders Guide to XXX Climate" in 4 versions for different climates. I have one and it is excellent, however mine is for hot-humid climates.

    Best of luck -- P.Student

  3. #3
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,064
    Consider all homes have warm, moist air exfiltrating out through the attics/walls/insulation during cold weather because of the "stack effect". Most homes leak enough air during cold weather to remove the internal moistue. Moisture condensing on cold windows is signal that more ventilation is required. At this stage, the exfiltrating air is very moist and condensation may occur in the insulation and on cold exterior. Increasing the ventilation rate will reduce the moisture content or dew point of the exfiltrating air. Reducing the dew point reduces the potiential for condensation. Therefore increasing the make-up air volume with an air cycler in usally not be a problem.
    All home need mechanical ventilation during mild weather and no wind. A good point is that a good bath fan exhausting 50-80 cfm when the home is occupied also provides fresh air. High humidity gets to be a problem when the outdoor dew points exceed 60^F. You need fresh air but must control the indoor humidity. In green grass climates, a good dehumidifier is requiree to maintain <50%RH to avoid mold or dust mites. We make an dehu with make-up air ventilation. Check out Santa Fe/Ultra-Aire. TB

  4. #4
    Join Date
    Oct 2005
    Posts
    3
    Thank you both for your insightful answers! I've checked out the web site for Building Science Corp. and intend to order the book P Student suggested. Thanks! Neal

  5. #5
    Join Date
    Apr 2002
    Posts
    11,808
    I guess when you lump in all houses old and new together you can use the term "Most homes leak enough air...."

    New homes however, can be so well sealed that there will be winter time condensation problems unless mechanical ventialtion is used
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  6. #6
    Join Date
    Jun 2003
    Location
    Madison, WI/Cape Coral, FL
    Posts
    6,064
    Homes with winter moisture problems need mechanical ventilation year around. Many homes without winter moisture problems need mechanical ventilation when the stack effect is not working. Just to be safe, use mechanical ventilation to make sure! TB

  7. #7
    Join Date
    Apr 2002
    Posts
    11,808
    An R2000 home will end up with 0.07 or less air changes per hour. They use this infiltration rate in load calcs if the house is 1, 2, or 3 stories high. No stack effect.

    A less sealed home will have a varying infiltration rate based on how high the building is due to stack effect changing with building height.

    Homes with winter moisture problems often may not have central ac. Good chance windows are open in the summer.
    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

  8. #8
    Join Date
    Jul 2004
    Location
    Southern Alabama
    Posts
    448
    Wouldn't you want to keep the house in a negative pressure in cold climates to keep humidity in?

    Wouldn't it be better to install an HRV and control the ventilation route better than using the house exfiltration?

    I like the idea of using an ERV (used in the South to remove humidity from outside air) and continuously ventilate from the points of contamination (kitchen, bath, laundry) and bring in fresh air into areas where people stay (bedroom, livingrooms).

  9. #9
    Join Date
    Apr 2002
    Posts
    11,808
    If you have a house in Canada and you find it necessary to run a humidifier, the house is drafty and is naturally changing its air. You will not need mechanical ventialtion except to get rid of odours.

    This would apply to an American Home as well. A dry house is a drafty house.

    If you have a tight home in Canada you will need mechanical ventilation else you will have a bad problem with condensation.

    An HRV is an excellent way to ventilate a new home in a northern climate and is even more appealing now with the rising energy costs.


    The way we build has a greater impact on our comfort, energy consumption and IAQ than any HVAC system we install.

    http://www.ductstrap.com/

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