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Humidifiers and temperature

Post in 'The Hearth Room - Wood Stoves and Fireplaces' started by DavidV, Dec 16, 2005.

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  1. DavidV

    DavidV New Member

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    I've been wondering about adding a humidifier to my house. I know the air dries out a bit in winter and the stove adds to that. What I'm wondering is if this will also effect my heating efficiency. it seems like dry air would be a less effective medium for heat than air that had a higher moisture content. Is there anything to back this up or am I full of it?

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  2. vgrund

    vgrund Feeling the Heat

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    It affects your perception of comfort. Dry air feels colder than humid air at the same temperature.
  3. roac

    roac New Member

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    It can work both ways I think. Think of a cold rainy day and how the humidity makes you feel colder. So I think there is a cut off there somewhere.
  4. Corey

    Corey Minister of Fire

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    I think the two sides of the equation are baed on your body's reaction to the humidity. If you are in an environment where you are sweating, the humidity adds to the percieved temperature because the sweat can not evaporate off your skin, so it seems hotter. If it is cold and rainy, it may seem colder because the humid air can pull more heat out of your body. Although I would wager that a 60 degree day at 90% RH would still seem warmer than a 60 degree day at 10% RH.

    I was reading up a bit on humidity earlier in the week...surprising to me was the fact that indoor RH "comfort zone" is about 45-50%. Seemed pretty low to me, but the claim was that above that level, mold, dust mites, etc tend to experience population explosions which can lead to the some of the same symptoms as low humidity. I went out and invested in a hygrometer and found that I was a lot closer to the comfort zone than I thought.

    Corey
  5. begreen

    begreen Mooderator Staff Member

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    Corey, I'm not following this. The body cools itself via evaporation of water from the skin surface via radiation and evaporation, aka sweat. In a dry interior environment, one is going to lose more body moisture. Thus one feels cooler. The drier it is, the faster the evaporation. One also might notice dry skin, chapped lips etc. as a result. However, I've never heard of humid air pulling more heat from one's body. What is this premise based upon?

    We have a lot of rainy cool days out here. It seems to me that on a rainy day - a, it will be above freezing, b, the dew point will be higher, and c, maybe you have less layers on or maybe you don't have the stove going as much. But if one is heating the house to 70 then I don't think that there will be any more heat drawn from one's body in spite of a measurably higher relative humidity on said rainy day.

    Of course, there is the psychological factor of just feeling colder when it's grey and gloomy and there is no warm sun to bask in.
  6. begreen

    begreen Mooderator Staff Member

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    Welcome back Frank. This is the science:

    Because of the large heat of vaporization of water, the evaporation from a liquid surface is a very effective cooling mechanism. The human body makes use of evaporative cooling by perspiration to give off energy even when surrounded by a temperature higher than body temperature. The cooling process is an example of the approach to thermal equilibrium.
    The cooling rate for a liquid (below boiling) is more complicated since the heat of vaporization changes with temperature, and the rate of evaporation depends upon ambient temperature and relative humidity.

    Sit naked in a 75 degree room and one will feel much cooler if the relative humidity is 10% vs 90%.
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