Dehumidifier in Basement Question

[marko]

This should be simple but forgive me because we've always lived in 150 year old houses until we built new last year. Never had this issue before--maybe we did but never thought about it.

So: One year old house. Basement is damp; builder originally suggested we might get a dehumidifier to keep mold and dampness in check.

Got a nice one that does the job, taking RH from ~70% to ~45%. (two monitors to confirm)

Wondering: Does the dampness ever go away? IOW, do the concrete walls and floor ever dry out to maybe like 55% RH (thanks to the removal rate) or, even after 10 years does it pop right back up to 70% the day after the machine is turned off?

 

[foxcreek9]

Not in my experience, never had a "wet" basement but left unchecked the RH would be about 65-70% most of the summer.

 

[Sunset]

In theory a new home will have higher humidity as it drys out.

But we have a basement de-humidifier as I noticed the humidity was too high (rust on tools).
We also turned off the furnace humidifier as it seemed silly to add humidity and then remove it.
It's been 20 yrs and still using it.
However, lots of Chicagoland was originally swamp, and we are one of the more rare houses with a full basement in our neighborhood.

 

[Trailwalker]

We run the basement dehumidifier continuously from May to end of September, unless we are gone from the house. Upon our return when it's off, the basement always smells musty. A couple of days later, it's fine. We spend a lot of time in our finished walk-out basement because it's comfortably cool in the summer.

 

[l8_apex]

We run the basement dehumidifier continuously from May to end of September.

I do the same. I'm in MT, and for the ~6 months that the ground is frozen, there is no need to dehumidify. When the ground is fully thawed and ground water is moving, I need to run the dehumidifier.

 

[skyking1]

It is a "feature" of basements to typically be as much as 15 degrees cooler than the floor above.
Take the same volume of air containing a given weight of water and cool it 15 degrees, and the relative humidity will go up a corresponding amount.
As long as the basement is cooler, the humidity will be higher than the house.
This is a good thing, because dehumidifiers are efficient down to about 45% Relative Humidity (RH).
The orher good thing about dehumidifiers is energy when heating.
Due to the law of conservation of energy, if you are heating with electricity, the humidifier costs nothing to run.
If you heat with a heat pump it is slightly more expensive for that dehumidifier heat.
I

 

[MichaelB]

Another seasonal dehumidifier user here, from spring ‘til mid-fall in our basement in the Chicago area. Amazing how much water is extracted from the humid summer air.

To answer the OPs question, yes, it’s probably forever, but only part of the year. It won’t go up the day after you turn off the dehumidifier, it might take 2 or 3 days.

If the ground around the house is humid, the basement will be as well.

 

[PaunchyPirate]

I’m in the same camp as several above. Northwest Pennsylvania here. Turn it on with Spring rains and run it until late Fall. 1960s home here and moisture seeps in thru the basement walls some.

 

[ls99]

I’m in the same camp as several above. Northwest Pennsylvania here. Turn it on with Spring rains and run it until late Fall. 1960s home here and moisture seeps in thru the basement walls some.

Ditto SW PA.

 

[Marita40]

Old house in MN and the basement dehumidifer just got turned on this week. It will run during the day from now until late September or so. I turn in off each evening and save some money that way; it works just as well doing so. Otherwise, basement would be clammy and smelly.

 

[joesxm3]

My house is built on what probably should be a swamp, with a very high water table. Probably would not be allowed as new construction today.

I had a huge problem with moisture in the basement. The paint peeled off the walls and at one point the labels came off my wine bottles.

About 10 years ago I did a massive project to correct the situation. I found this stuff on Amazon called Radon Seal. You spray it onto your concrete wall or floor and it soaks in and then does some sort of crystalization process that pushes out all of the white stuff that had been seeping out of the damp concrete. It fills in all of the pores in the concrete and once it hardens is extremely water proof.

I bought a Bosch concrete surface grinder and used that to clean the walls and floor before and after applying the Radon Seal. For the floor I bought their more expensive product called Ion Bond Armor. This is made to use in situations where you are laying a wood floor over the concrete, but I just used it for the concrete floor. After I was finished I painted the walls and floors.

I have two sump pumps that run year round, quite often. They still do and I imagine that they are dealing with the water outside the foundation. Like I said, my house is more like a boat.

I run dehumidifiers in each of the two major rooms of the cellar and it keeps the humidity level to about 40. One of the rooms is the garage and it is not very well sealed so moisture probably comes in through the garage door.

However, the Radon Seal worked great. I can put a drop of water on the floor and come back the next day and it is still there.

I run the dehumidifiers from May to October or November.

 

[euro]

This should be simple but forgive me because we've always lived in 150 year old houses until we built new last year. Never had this issue before--maybe we did but never thought about it.

So: One year old house. Basement is damp; builder originally suggested we might get a dehumidifier to keep mold and dampness in check.

Got a nice one that does the job, taking RH from ~70% to ~45%. (two monitors to confirm)

Wondering: Does the dampness ever go away? IOW, do the concrete walls and floor ever dry out to maybe like 55% RH (thanks to the removal rate) or, even after 10 years does it pop right back up to 70% the day after the machine is turned off?

More than likely, you'll always need to dehumidify. The ground around the basement walls is always moist enough (except, maybe if it is frozen solid in the winter as other posters suggest) and concrete is porous. I used to have a rental property with a basement apartment and we had to pretty much run dehumidifier 24/7 year round to avoid mildew/mold. House was 50+ years old in NC (pretty darned muggy here, especially in the Summer.... sigh).

 

[Sunset]

We just leave our dehumidifier "on" all the time, it has a sensor on it, so it turns itself on/off depending upon the humidity levels.

Sometimes it doesn't run hardly at all, mostly in the Winter it's off.

 

[Jerry1]

We just leave our dehumidifier "on" all the time, it has a sensor on it, so it turns itself on/off depending upon the humidity levels.

Sometimes it doesn't run hardly at all, mostly in the Winter it's off.

That’s what I did when I had a basement (now on a slab). Get a dehumidifier with a sensor and keep your basement at whatever level you’re comfortable with. Mine didn’t have a reading, just a “hi” to “low” dial. Also make sure to run a hose from the dehumidifier to a drain or your sump pump so you don’t have to empty the bucket of water it creates.

 

[RunningBum]

Timely reminder, I just set my dehumidifier on in my basement. Actually you guys should have reminded me a month ago. Do better next year, ok?

I also emptied the container for my house humidifier that runs through the furnace vent. That should have been done in March. Better late than never.

 

[Walt34]

Northern WV here. Like most we also run a dehumidifier* from spring (mid May) until about November or December. It will run constantly and then not at all in the winter. The same was true when we lived near Washington, D.C. which is not surprising since that area is well-known for high humidity.

Concrete is porous and the water from outside will infiltrate unless you go to some rather drastic (and very expensive) measures to block it. A dehumidifier and the electricity to run it is much, much cheaper and easier.

*Actually we run two of them but the second one was bought after a dishwasher leak upstairs and isn't strictly needed but since we have it we figured we might as well use it. The basement is a large one and we put one at each end. Both also empty into condensate pumps of the type normally used with central A/C units and are very reliable (one moving part). Except for an annual inspection/cleaning of both dehumidifiers and condensate pumps they are pretty much "set and forget".

 

[CardsFan]

Marko,

If I recall correctly, you are in MA. When we lived in Worcester, in a house with no A/C, we had a very musty basement until buying a dehumidifier and running it constantly from spring through fall. I was on in the winter but did not run much.

It made a world of difference.

 

[marko]

Thanks to the collective wisdom! This answers my curiosity.

I was amazed after the first night where about a gallon of water had collected! I now drain directly into a sump pump so I don't have to empty the bucket anymore.

 

[ERD50]

This is very location and situation dependent. Your profile says Florida - I thought basements were rare to non-existent there? But I'm sure it is humid.

IME, I've found keeping the RH between 55% and 60% was adequate for our summer months, we don't need to run it at all from late Fall to late Spring. Then we need to humidify (the upstairs) in the Winter.

In our previous home, the basement was unfinished, I didn't bother with a de-humidifier, but would open vents so the AC would take some out. But it got high enough to get dank and some musty smell. Tools got a little rust on them sometimes.

So when we moved last year to a finished basement, I got a de-humidifier, and wished I had bought one for the old place way back. It's nice to just feel comfortable down there, and know you aren't going to get any musty smell,. so no worries about storing anything there.

New construction (especially cement) will give off more moisture for months, maybe even a year, I would think. But as others have said, depending on your climate, you can expect to need to de-humidify at least during any humid seasons.

Oh, since I'm retired, I got into a habit of checking the humidity in the AM, and just turning it on and letting it run (manual mode - full ON, not auto-cycling) until it dropped 5 or 6 points (several hours to most of the day sometimes). Seemed that when I left it on 'auto' it cycled on/off a lot, running only 5 minutes at a time, and I don't think that's good for efficiency. If I was not going to be able to check it, I'd set it to auto.

Just turned it on now for the season - basement got to 66%, while the AC was keeping upstairs at between 52%~55% ( @ 77F). As mentioned earlier, since it is cooler in the basement (66F now, was 64F a few days ago), the RH is higher for the same actual water content, as cold air holds less moisture. So even circulating the air will have a higher RH down there.

This is the model we have, and my son bought one too, seems to work fine:

https://www.homedepot.com/p/GE-50-p...ree-Fan-Speeds-ENERGY-STAR-ADEL50LZ/312405764

-ERD50

 

[marko]

This is very location and situation dependent. Your profile says Florida - I thought basements were rare to non-existent there? But I'm sure it is humid.

Thanks. We winter in Florida, but summer north of Boston. I need to update my profile!

 

[Midpack]

Another seasonal dehumidifier user here, from spring ‘til mid-fall in our basement in the Chicago area. Amazing how much water is extracted from the humid summer air.

To answer the OPs question, yes, it’s probably forever, but only part of the year. It won’t go up the day after you turn off the dehumidifier, it might take 2 or 3 days.

If the ground around the house is humid, the basement will be as well.

+1. Depends on humidity of outside air, which depends on what area of the country you’re in. We have a dehumidifier in our crawl space, it runs a lot in summer when it’s humid, less in spring/fall and almost never in winter, ours it set to maintain 55% or below year round. As for drying out a wet basement, you’ll reach an equilibrium that follows ambient humidity. If you need a dehumidifier, it’s permanent if you want to avoid mold, insects, wood rot etc.

With a properly sized automatic dehumidifier, basements and crawl spaces are pretty maintenance free, and handy spaces - we’ve had houses on slabs, crawls and basements, and we miss having a basement.

 

[W2R]

Good heavens! Basements sound like a lot of work. They are rare here in New Orleans, and after reading this thread I'm glad that neither Frank nor I have one.

 

[folivier]

Our new to us cabin in the Colorado mountains has a basement. Part of it is concrete floored the other half is just dirt and is open for about 10' to the other half. Never having a basement before (I'm from south Louisiana also) I just looked at my Ambient sensor and humidity is 61%. That's just above what our house in Louisiana averages inside with AC running. Hard to get it much lower than that.
Anyway it doesn't seem damp to me and there is no mold that I can see. But I'm on a slope so would think any moisture would not accumulate much.

 

[Music Lover]

This should be simple but forgive me because we've always lived in 150 year old houses until we built new last year. Never had this issue before--maybe we did but never thought about it.

So: One year old house. Basement is damp; builder originally suggested we might get a dehumidifier to keep mold and dampness in check.

Is it a concrete foundation? It will be cured in a month but could still give off moisture for a year or so.

 

[travelover]

Good heavens! Basements sound like a lot of work. They are rare here in New Orleans, and after reading this thread I'm glad that neither Frank nor I have one.

I think if you dug a basement in New Orleans, you would have a swimming pool.