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  1. #1
    Join Date
    Aug 2003
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    907

    Safely maximizing humidity in freezing weather

    Here's a question to take your minds off the hot weather .
    I understand that in a cold climate, the humidity levels in a house need to be lowered as the outside temperature goes down, to prevent condensation inside the walls or in the attic insulation. I have seen generic guidelines based solely on the outside temperature but I think these are oversimplifications because the real situation would have to depend on how tight the home is, the number of floors it has to create a stack effect, the inside temperature, winds, etc... Also, the maximum humidity should probably be based on the condition of the insulation of the top floor, where the pressure should be higher than in the basement, therefore causing more humid air leakage and a greater risk of condensation. Is there a measurement that can be done so that I can have as much humidity inside as is safe and have some peace of mind and proof that there really is no in-wall condensation happening? Has anyone experience in safely maximizing humidity levels during winter (up to a maximum of 40% or so)? How is that done with appropriate measurements (not just an outside thermometer) and hopefully no guesswork?

  2. #2
    Join Date
    Apr 2002
    Posts
    11,808
    the windows are the most prone to condensation in a tight home.

    Well sealed houses with high end windows can hold 40% in the winter.

    In a cold climate it is possible to build and have next to no infiltration
    Last edited by Carnak; 07-11-2007 at 07:51 AM.
    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/

  3. #3
    Join Date
    Aug 2003
    Posts
    907
    Quote Originally Posted by Carnak View Post
    the windows are the most prone to condensation in a tight home.

    Well sealed houses with high end windows can hold 40% in the winter.

    In a cold climate it is possible to build and have next to no infiltration
    Thanks. This is a 75-year old house with new, fairly high quality windows, and insulation blown in the walls and in the attic (well-ventilated attic). It's probably still leaking like a sieve though. Should I believe that as long as there is no condensation on the windows, it is *probably* safe? Would a blower door test and thermal imaging scan to find and fix leaks be worth the money, or should I just give up now and move to a new home, if my goal is to enjoy 30-40% humidity even on the coldest days during Indiana winters? Are there numbers to know how tight is "well sealed" enough for that goal?

  4. #4
    Join Date
    Apr 2002
    Posts
    11,808
    The homes with the continuous sealed vapour barriers could do it, but this is not your case at all.

    going to need a well ventilated attic.

    would also be best if the home was slightly negative pressure all the time. Should not be impossible if your combustion appliances are direct vent and it is not a radon prone area.
    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/

  5. #5
    Join Date
    Aug 2003
    Posts
    907
    Quote Originally Posted by Carnak View Post
    The homes with the continuous sealed vapour barriers could do it, but this is not your case at all.

    going to need a well ventilated attic.

    would also be best if the home was slightly negative pressure all the time. Should not be impossible if your combustion appliances are direct vent and it is not a radon prone area.
    Yes, the furnace uses direct vent (sealed) combustion and all the rest is electric, so there can't be any backdrafts. There is a little bit of radon, but not enough to be a concern (well below the EPA action levels). Thanks!

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