Basement dehumidifier

[KC]

100+ year old house.  Roughly 500sf basement, with an similarly sized 'open' crawlspace on one side (from an addition), and another crawl space from the original build at the other end that's effectively closed off, but none of the space around ductwork is sealed.  Floor is concrete.

Basement isn't wet, and there's no noticeable mold, but it's certainly musty and 'damp'.  Humidistat thingy said 70% down there, 55% upstairs.   So we got a dehumifier yesterday.  Humidistat thing says it's down to 57% in the basement; display on the humidifier says 60% (advertised +/- 5%)... so it seems to be working.  Dumped the bucket a couple times in the 18 hours it's been on.  

Question is, can I expect the water collection to slow down as the humidty stabilizes at the 'new' normal of 50% (or whatever that number is)?

[jteneyck]

100+ year old house.  Roughly 500sf basement, with an similarly sized 'open' crawlspace on one side (from an addition), and another crawl space from the original build at the other end that's effectively closed off, but none of the space around ductwork is sealed.  Floor is concrete.

Basement isn't wet, and there's no noticeable mold, but it's certainly musty and 'damp'.  Humidistat thingy said 70% down there, 55% upstairs.   So we got a dehumifier yesterday.  Humidistat thing says it's down to 57% in the basement; display on the humidifier says 60% (advertised +/- 5%)... so it seems to be working.  Dumped the bucket a couple times in the 18 hours it's been on.  

Question is, can I expect the water collection to slow down as the humidty stabilizes at the 'new' normal of 50% (or whatever that number is)?

Maybe.  It depends upon how leaky the basement is to air ingress and moisture seeping through the concrete and ground or whatever is under the crawl spaces.  I have poured concrete walls and floor in my basement, all painted, and the rim joists spaces are sealed fairly well, but the dehumidifier still runs regularly as the RH goes up outside in the Summer.  I have it set at 55% and as soon as the outdoor RH climbs much higher than that the dehumidifier starts running.  

John

[branchacctg]

First house forty-five years ago had a full basement that was like yours very must and dank.  After a month of getting settled in, we got a portable dehumidifier and put it in the basement.  Had to empty it three or fours times a day for about a week.  After that maybe once every other month.  Best guess is that previous owners left the windows and doors open and the outside humidity came on in and stayed. Had no problems like crawl space to deal with.  Good luck on yours,

[KC]

Thanks for the replies!

[Snipe Hunter]

Question is, can I expect the water collection to slow down as the humidty stabilizes at the 'new' normal of 50% (or whatever that number is)?

No. Well, maybe a little

The dehumidifier is pulling moisture from your walls and floor as well as from the air. There is still moisture behind those walls and it will always wick through. The drier the air the faster the moisture migration. You also have basement walls and a floor that are in contact with the earth somewhere around 55 degrees. So interior humidity will always condensate on the basement walls and floor. All you are doing with the dehumidifier is pulling moisture from the air which will make the moisture on your floor and walls evaporate into the air faster... feeding more humidity.

A moisture meter (even a cheap one) will tell you where your surface moisture is most prevalent. Any surface moisture above 19% mc (moisture content) will sustain mold growth.

Basements are the coolest area in the house so all the moisture in the air in the house will migrate to the basement to condense in the air and on the walls and floor.

Musty smells are generally caused by wet, bare earth or mold spores in the air.

You can use a moisture barrier paint like Dry-Lock to help slow moisture intrusion through the walls. Vinyl plank flooring or a painted floor will help prevent moisture intrusion from the floor. A properly installed 6mil plastic vapor barrier over the crawlspace floor will help prevent moisture from the bare earth. So will insulating the walls in the basement and crawlspace but that can contribute to some other "trapped moisture" problems and mold behind the insulation or vapor barrier on the walls. If your crawlspace floor isn't covered with a vapor barrier, that is most likely where most of your easily controllable moister is coming from. I don't remember the numbers from my training but gallons of water can pass through a pretty small opening in a single day. If your crawlspace has a higher humidity level than the outdoors, a powered crawlspace vent and make-up air vents, plus the vapor barrier and sealing around any penetrations between the crawlspace and the basement will help a lot.

Air movement is also important to reducing the mc in the air. Ideally, seal off the crawlspace and vent it and air condition the basement. An air conditioner will remove a lot more moisture than a small stand alone dehumidifier.

I would connect the dehumidifier to a drain or a condensate pump. You will get tired of emptying that bucket.

[Red Sawman]

Keep the area around it clear and .... don't forget to clean the filter and the coil once in a while ... DAMHIK

[KC]

No. Well, maybe a little

The dehumidifier is pulling moisture from your walls and floor as well as from the air. There is still moisture behind those walls and it will always wick through. The drier the air the faster the moisture migration. You also have basement walls and a floor that are in contact with the earth somewhere around 55 degrees. So interior humidity will always condensate on the basement walls and floor. All you are doing with the dehumidifier is pulling moisture from the air which will make the moisture on your floor and walls evaporate into the air faster... feeding more humidity.

A moisture meter (even a cheap one) will tell you where your surface moisture is most prevalent. Any surface moisture above 19% mc (moisture content) will sustain mold growth.

Basements are the coolest area in the house so all the moisture in the air in the house will migrate to the basement to condense in the air and on the walls and floor.

Musty smells are generally caused by wet, bare earth or mold spores in the air.

You can use a moisture barrier paint like Dry-Lock to help slow moisture intrusion through the walls. Vinyl plank flooring or a painted floor will help prevent moisture intrusion from the floor. A properly installed 6mil plastic vapor barrier over the crawlspace floor will help prevent moisture from the bare earth. So will insulating the walls in the basement and crawlspace but that can contribute to some other "trapped moisture" problems and mold behind the insulation or vapor barrier on the walls. If your crawlspace floor isn't covered with a vapor barrier, that is most likely where most of your easily controllable moister is coming from. I don't remember the numbers from my training but gallons of water can pass through a pretty small opening in a single day. If your crawlspace has a higher humidity level than the outdoors, a powered crawlspace vent and make-up air vents, plus the vapor barrier and sealing around any penetrations between the crawlspace and the basement will help a lot.

Air movement is also important to reducing the mc in the air. Ideally, seal off the crawlspace and vent it and air condition the basement. An air conditioner will remove a lot more moisture than a small stand alone dehumidifier.

I would connect the dehumidifier to a drain or a condensate pump. You will get tired of emptying that bucket.

Been two or three days... I'm tired of emptying it already.  


No floor drain down there.   Big hole about three feet deep that suggests someone was thinking ahead for a sump pump (or maybe just for water to go in an emergency... no piping).   I probably can run it into the condensate pump on the air handler.  There are a couple ducts for heat and air down there, so some air is moving.  

Crawlspace is bare dirt.  

I've spent as long as maybe an hour down before and there and it wasn't uncomfortable.   This was one of those things Jean though might be a good idea.  Hard to argue against since the monitor says the humidity is hella lower in the basement when it's running, and 10% lower upstairs.

That said, in the three or four minutes it takes me to carry the bucket upstairs to empty it and put it back, the monitor reading will start going up immediately.   Since the house has been here for a whole long time and nobody's sick, I wonder if the 'good' is worth the bother?

[Snipe Hunter]

Since the house has been here for a whole long time and nobody's sick, I wonder if the 'good' is worth the bother?

Mold is funny stuff. It affects everybody differently. That's why there's no federal/epa standards for safe or unsafe levels. Because of that, anybody can go into business as an Indoor Air Quality Tester/Consultant. Nobody regulates them.

People ask me to test the air for it if I point it mold in their home. I say... why? I can see it. If I can see it, it's there. I can test it to find out what kind it is but what difference does it make? About the only time I test for it is if someone in the house keeps having respiratory problems of if I or someone else smells  a "musty" odor. I do 2 outdoor air samples and usually 1 indoor air sample. If the spore count is higher indoors, there's a mold problem. Along with that test, I record the moisture content of the walls, floor and building materials and check the humidity. And I do a visual check. It's hard to see it in a crawlspace if it's in the dirt or in the insulation.

I got sick a year ago Christmas after going into a crawlspace. Should have worn a mask.. I could smell it. The air was so wet in the crawlspace, I could push a screwdriver through the joists. They were intact but rotted. I could feel the soft floor in the house walking on it. That was the only house where mold made me sick. There would have been another but I got out pretty quickly and told the client that I wouldn't go back in. There was black mold up to eye level on the basement walls and on the basement ceiling and the entire carpet was damp. It had been empty a few years. The outdoor basement stairwell drain was covered with about 6 inches of rotted leaves.