Another humidity question

chris_ontJuly 12, 2006

Hi

I can't seem to wrap my head around this one. Does a cool basement in humid weather increase humidity in the home?

I have a century home that has the odd leak and some moisture coming up through the poured concrete floor (no standing water, just dark spots).

The air conditioning keeps the basement colder than the upstairs. Does this cause undue amount of condensation downstairs? Should I close off some of the basement AC vents?

There is a dehumidifier down there, set at 50% which seems to be running pretty much non-stop.

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formulaross

"Does a cool basement in humid weather increase humidity in the home?" Let me rephrase the question to: Does a humid basement increase humidity in the home? The answer is yes. The basement represents an area of high humidity, the home above an area of low(er)humidty. The second law of thermodynamics says that systems tend to go towards equilibrium, so the humidity in the basement will try to go towards the humidity upstairs and bring both to the same level.

"The air conditioning keeps the basement colder than the upstairs. Does this cause undue amount of condensation downstairs?" I guess only you can be the judge of that. Are you condensing sufficient moisture to literally make the basement wet?

"There is a dehumidifier down there, set at 50% which seems to be running pretty much non-stop." You might consider a larger capacity dehumidifier. Or, consider limiting moisture entry into the basement by sealing the walls/floors with drylock types of paints and sealing all air leaks from the outside to the basement (air flow can carry significant amounts of moisture).

Hope this helps.

    Bookmark   July 14, 2006 at 9:37AM
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behaviorkelton

May I piggyback?

I'm interested in this topic.
If humidity does indeed "even itself out", by traveling to areas of lower humidity....
Does that mean that I can put a dehumidifier basically anywhere in the basement area and expect it to be effective even in the farthest reaches of the basement?
IOW: Is there any special advantage to putting the dehumidifier in a particular location or can you put it anywhere?

    Bookmark   July 15, 2006 at 5:14PM
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diymostoftime

I have the same question as behaviorkelton. Can anyone help....?

"If humidity does indeed "even itself out", by traveling to areas of lower humidity....
Does that mean that I can put a dehumidifier basically anywhere in the basement area and expect it to be effective even in the farthest reaches of the basement?
IOW: Is there any special advantage to putting the dehumidifier in a particular location or can you put it anywhere?"

    Bookmark   August 8, 2006 at 7:42PM
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twatters

The amount of water dissolved in your home's air upstairs and downstairs will eventually become equal, but relative humidity depends on the temperature as well. Warm air can dissolve more water than cool air. If the amount of moisture in the air is exactly the same up and downstairs but the temperature downstairs is cooler, then the relative humidity downstairs will be higher. When the relative humidity reaches 100% condensation occurs. This often happens on cool surfaces such as basement tile, concrete walls, cold water pipes, etc..

To lower the relative humidity in your basement you can close it up can put a dehumidifier down there. If it's open (open windows, open stairwell to upstairs, etc.), then you'll spend alot of money trying to dehumidify your entire neighborhood.

Another way to lower the relative humidity in the basement is to insulate the basement walls and floor and/or raise the temperature. This is probably the best long term solution.

Another way to raise the temperature of the basement is to put in a continuous running exhaust fan down in the basement and allow it blow cool air out of the basement and pull warmer air from upstairs through on open stairwell or floor registers. This is cheaper than running a dehumidifier and gets some warmer, dryer, and fresher air into the basement. It may be enough. However, if your climate is hot and muggy, then sealing the basement and running a dehumidifier may be your only option.

    Bookmark   August 9, 2006 at 8:57AM
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jayh

So it is better to blow air out of the basement rather than blow air in?

I just bought a window fan I can stick in the basement windows and was just wondering. Lately I've been simply taking a large fan on a stand and blowing warmer air from the outside in. I would blow air into the basement from the outside, only when the outside humidity was low and I would try to close the windows whenever the outside air was relatively humid.

With my window fan, I have the option of using it as an intake or exhaust with the simply moving of a switch.

Jay

    Bookmark   August 10, 2006 at 1:30PM
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PRO
The Metal Peddler

I'd love to know how to get this balance right. We run 2 dehumidifiers 24/7 and barely manage to keep below 60%, more often 65%. But if we close off ventilation to stop the humidity coming in from outside, then the air gets horribly stale. We also have a window fan set to exhaust OUT but have a small window opened to allow air in for circulation.
I want drier air but also want cleaner fresher air...

    Bookmark   August 11, 2006 at 12:09PM
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twatters

> So it is better to blow air out of the basement rather than blow air in?

Blowing (or allowing) warm HUMID air into a cool(er) basement will probably result in very high relative humidity and condensation in the basement.

> Lately I've been simply taking a large fan on a stand and blowing warmer air from the outside in

Try blowing the basement air OUT and be sure that the air will be replaced by warmer/dryer air from upstairs (not from outside humid air). You can do this by opening the basement/upstairs door or installing a register to allow air flow from upstairs to downstairs. Keep all other basement windows closed. Let it run continuously and see what happens. This is what Humidex, EZ Breathe, and Musty Basement Solution systems do. They cost about $1000-$1500 however. Your window fan might accomplish the same thing.

    Bookmark   August 11, 2006 at 2:27PM
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