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  1. #1

    realative humdity question

    if you had to set realative humdity to say 20% for -20 degrees, you would choke from it being to dry.

    i Live in michigan, have my humidistat set at 40%, if i go any lower 37-38% me and my wife will wake up with dry throats choking.

    My windows condensate pretty bad when the temperature is 15 degree F outside. but i can't go any lower on the humidity cause of the dry throats.

    Outside Temperature Inside Humidity
    20 to 40F Not over 40%
    10 to 20F Not over 35%
    0 to 10F Not over 30%
    -10 to 0F Not over 25%
    -20 to –10F Not over 20%
    -20F or below Not over 15%

  2. #2
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  3. #3
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    Quote Originally Posted by smooth2222 View Post
    if you had to set realative humdity to say 20% for -20 degrees, you would choke from it being to dry.

    i Live in michigan, have my humidistat set at 40%, if i go any lower 37-38% me and my wife will wake up with dry throats choking.

    My windows condensate pretty bad when the temperature is 15 degree F outside. but i can't go any lower on the humidity cause of the dry throats.

    Outside Temperature Inside Humidity
    20 to 40F Not over 40%
    10 to 20F Not over 35%
    0 to 10F Not over 30%
    -10 to 0F Not over 25%
    -20 to –10F Not over 20%
    -20F or below Not over 15%
    Measure the actual humidity in your bedroom at night. You may find that it is not a high as the area the humidistat is in. Your bedroom may have a lot of air leakage.
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  4. #4
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    The cause of low humidity in a home is a result of warm air leaking out of the home and being replaced by cold air that must be warmed to a useful temperature. Most everyone knows that cold air can hold less moisture than warm air. % humidity is called RELATIVE HUMIDITY because it's predicated on the air temperature. A cubic foot of air at 30F can hold way less moisture than that same cubic foot of air when its temperature is 70F. So if 70F air leaks out through the roof/attic of your home, the laws of nature/physics dictate that an equal amount of air needs to infiltrate your home to replace it. Thus, when it's 30F outdoors, that's what leaks into your home. When the heating system raises that 30F air to 70F for your comfort, the RELATIVE HUMIDITY takes a nose dive. Thus, if the air infiltrating is 50% RH when it enters the home, is then heated and the RH drops WAY down. So the first need to solve a low humidity problem is to stop the exfiltration (leakage) from the home to cut the infiltration. This is all quantified with a blower door test and the calculated ACH (air changes per hour). A tight home will be in the range of .25 ACH, while an average home is around .5 ACH and really leaky home can be anywhere from .8 ACH to over 1.0 ACH. Put another way, a tight home (requiring mechanical ventilation) has a total of 4 air exchanges in a 24-hour period, an average home about 12-air exchanges per 24-hours and a loose home anywhere from 18 to 24+ air exchanges per 24-hour period.

    By now it should be obvious that a loose home needs gallons and gallons of water added to the rapidly changing cold air that's heated and quickly exfiltrates the home as it's warmed due to chimney affect (warm air rises and the colder it is outdoors, the faster it rises up and out). An average home needs less moisture added to the air and a tight home needs little on none added as normal living conditions (showers, breathing, cooking, laundry, etc. all add moisture naturally) tend to add moisture and the ACH is so low it can sometimes be all that's needed. Otherwise a minimal amount of moisture can be added, mechanical ventilation is required and proper control over the moisture content is essential so that humidity doesn't get too high and create mold or mildew problems.
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  5. #5
    I have no problems mainting a humdity of 40%. the problem is the condensation on the windows. I can't lower any less than 37-38% or i'll wake up very dry throat, and sometimes even choking, same as my wife.

  6. #6
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    Quote Originally Posted by smooth2222 View Post
    I have no problems mainting a humdity of 40%. the problem is the condensation on the windows. I can't lower any less than 37-38% or i'll wake up very dry throat, and sometimes even choking, same as my wife.
    Might need to look into getting triple pane windows then.
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  7. #7
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    Maybe buy a small portable humidifier just for your bedroom to use when you are sleeping, and leave the rest of the house's humidity lower.

  8. #8
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    It's called dewpoint. The surface temp of your windows and frames are below dew point and water vapor condenses on the cold surface. That's why your humidistat has that crude scale on it. As was mentioned one fix is to get better windows. Also the window cover products that you shrink with a hair drier might give you a lower dewpoint and allow you to raise your humidity level.
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  9. #9
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    Quote Originally Posted by beenthere View Post
    Might need to look into getting triple pane windows then.
    Depending on if he has a vapor barrier and the amount of wall insulation, the next place moisture will condense is much, much worse than windows. Inside walls, around the window frame. Triple pane window will help glass surface temps a little, but they won;t improve the window seals or window frames. THe better ones have heavier aluminun extrusions... but at hte cost of thermal bridging. The heavy frames reduce warranty claims, help get the window to survive maybe 20 years, and don't significantly impact the overall U factor that they are targeting... that little window sticker. It's sort of like how automakers oftne spec low rolling resistance tires on a car and 0W20 oil to squeeze that last 1mpg.

    I'm sometimes suprised that 20-30% RH is "too low" inside a home, yet most people work in offices without humidification where the RH is around 10% most of the winter.


    There is a point at which the dry throats could be the opposite issue. Mositure is too high and with all that condensation you have some mold growing that you might have a mild allergy too.

    Try this... get a cheap protable humidifier and sleep wth your bedroom door closed. If you humidify you bedroom to 45% overnight and your throts are still dry, I recommed a specialst... a Ear/Nose/Throat physician or an allergist.

    Where I am in Iowa is actually a little dryer than most of MI. 20-30% is the most I maintain due to the older leaking windows I have. I have good storms so surface temps are high on the inside of the prime window, but I get excessive moisture between the panes upstairs if I keep it too humid. It's does give very, very clear evidence of stack effect. Abosulutely no codnensation between the downstairs window panes (air is being driven inward) but plenty upstairs. All of my appliances are direct vent and fireplace is out of service and sealed off.

  10. #10
    IF i leave it at 40% i'm fine, no dry throat or choking, so don't think its mold allergy. only condensate when its below 15 degrees outside, which isn't to often, but more so over night. house is only 15 years old.

    in 2 windows, I have fogging inside, inside between the panes, having someone come out tuesday to check em out and replace em. When i get the new windows i'll compare em to the other windows to see if the older windows are condensating more.

    "I'm sometimes suprised that 20-30% RH is "too low" inside a home, yet most people work in offices without humidification where the RH is around 10% most of the winter.
    "

    when at work or the office you are always swallowing, vs when you are sleeping you really don't

  11. #11
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    Just saying that 40% is a little high for 15F. I remeber getting frost on the baseboards in my last home if the humidity was that high when it dropped to near single digits.

    Thsi gives an overview. http://www.cottagestocastles.biz/pdf/misc/Humidity.pdf

  12. #12
    very nice article there, thanks. well gotta replace the 2 windows anyways, so will see what happens compared to the other windows.

    thank you everyone for commenting and posting

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