High temp but low humidity issue

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Old 06-14-15, 02:39 PM
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High temp but low humidity issue

I have a closed off crawlspace and I placed a dehumidifier in the crawlspace to bring down the humidity. It now reads anywhere from 25% - 30%. However, the temp is anywhere from 70 - 85. Is this a problem? It's basically a sealed crawlspace with a door. There really is nothing else I can do here.
 
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Old 06-14-15, 02:52 PM
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The dehumidifier may be adding the heat. I don't think it is a problem but with the humidity being controlled that low you may be able to raise the set point a bit and get the machine to cycle off and that would both save money on electricity as well as lessen the heat build up. A relative humidity of 40% is not high.
 
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Old 06-14-15, 03:06 PM
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I can raise to 40%. I also have a HEPA UV filter in there w fan to kill any airborne mold spores. Trying my best to keep it under control. There were boxes in there, but no mold visible. There were in there for 10 + years. I did a mold test and there was ASP on the pipes. No fuzzy or dark parts on the wood beams or insulation. I may replace the insulation in the fall or winter when it's a bit cooler in the crawlspace. So I treated the entire room with a FDA approved Biocide spray and fogger.
 
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Old 06-14-15, 03:37 PM
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A couple of points. Something in excess of 50% of the air you breathe in the winter comes from the basement or crawlspace. In the summer the natural circulation reverses so what you are putting down there is hopefully leaking to the outside. House to foundation is usually the primary leak to the outside.

Your current readings would be about 30% at 70. I added the RH calculator below. As Furd said you can bring that up a bit, except if you are in the process of drying things out. A crawlspace doesn't object to low humidity like people do.

As a general guideline, a crawlspace is either vented to the outside with the floor above sealed and insulated, or the crawlspace is sealed and insulated to the outside and then conditioned with heat and air conditioning just hike your living space. Just sealing up the crawlspace seems to fall inbetween.

Bud
Temperature, Dewpoint, and Relative Humidity Calculator
 
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Old 06-14-15, 04:00 PM
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Hello Bud,

Thank you for this information. I am just reading what is on the separate humidifier reader. It currently says temp 82 degrees, humidity 26%. Then a High arrow. I assume that is due to the temperature. I will contest, it is a bit hot in there. There does not seem to be any vent to the outside that I can see. There's four sides of solid concrete (one with a door), several inches of spray foam, and a ceiling with pipes and insulation. I will raise to 40% instead of continuous run.
 
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Old 06-15-15, 05:12 AM
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Do you have a proper vapor barrier? Do you even need to run the dehumidifier?
 
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Old 06-15-15, 11:36 AM
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If the dehumidifier is not running, the humidity in the crawlspace is over 70%. It's running most of the day. Not sure of the vapor barrier as the whole room is solid concrete (foundation).
 
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Old 06-15-15, 01:10 PM
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Sounds like you need to install a vapor barrier over the concrete.
 
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Old 06-15-15, 01:25 PM
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I'm guessing here, but if the crawlspace extends under the deck and the deck is somewhat open to the outside then your dehumidifier is trying to dehumidify the outside air along with the contribution from the walls and floor.

NY includes a variety of locations, but if I use Buffalo it is currently 70 and 92% RH. Albany is 71 at 71% RH. Ithaca 82 at 67 RH. So basically your crawlspace is filled with outside humidity. Remember, ALL of the air inside your home, including that crawlspace gets replaced with outside air every 2 to 4 hours.

Bud
 
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Old 06-16-15, 03:37 AM
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I live in downstate on the Island. There is no deck. The unit is sealed. There is no vents so I do not see how air from the outside is coming in.
 
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Old 06-16-15, 05:36 AM
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Sorry, wrong thread, the other has a deck leaking into the crawl area. In any case, airman's question was, do you have a vapor barrier. If it is a dirt floor then that is where one is definitely needed. Even if it is concrete, the question as to where the moisture is coming from still needs to be answered and from the outside is one of the possibilities. Where the building rests on the foundation is often a source of leakage. While you are running the dehumidifier and raising the temperature, you are increasing the natural leakage, cold air pushing in to displace that lighter warm air.

Basements or crawlspaces should not be sealed off from everything. They are either sealed from the outside and insulated and then conditioned by the heat and air conditioning as part of the house, or the floor is insulated and sealed from the house and the crawlspace is vented to the outside.

As for air leakage, a basic rule for acceptable air quality is to replace all inside air every 3 hours. Homes that are tighter than that require air exchange systems to get back to that number. On LI I'm sure you have energy codes in place with a requirement similar to that.

Bud
 
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Old 06-16-15, 06:14 PM
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Not sure on the codes. The house is 20 years old. The floor is concrete, not dirt. I can install a vapor barrier on the walls and floor, it seems easier enough. However, the previous owner left some very heavy (several hundred pound old stoves and things which are nearly impossible to move. It's only about 2 sq ft or so. Can I just cut around that area and place the vapor barrier on and under everything else?
 
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Old 06-16-15, 07:10 PM
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Something isn't right.
Where is the dehumidifier draining to? Does it go to a floor drain, a sump, or is it pumping it out to some place? Have you noted how much water it is removing?
The one door, does it open to the outside or to a basement area?
Is there any opening between the crawlspace and the house?

Bud
 
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Old 06-17-15, 05:12 AM
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Initially, the first week, it was filling up 50 pints a day in a 70 pint unit. It's now only a few pints a day. The unit has a collection bucket which I empty out. There is no way to run a hose, I had a plumber check. It's in a solid concrete room on three sides an the floor. I check the unit daily. I emptied it last on Sunday. Checked it today, only a few pints in there out of 70. Basically not much. The door opens to the basement, that is all. Not that I can see. I checked around the house for vents as well, but none was found.
 
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Old 06-17-15, 05:48 AM
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With the door opening to the basement, what is the humidity level in that space? If the basement is conditioned to maintain a reasonable level, now that you have the mess in the crawlspace cleaned out, can't you share, open the door? Since you are now collecting a minimal amount of water, whatever is controlling the humidity in the main basement should easily handle a little extra.

Bud
 
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Old 06-17-15, 08:09 AM
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The basement also has a dehumidifier. I am not sure, even with the door wide open it will be able to dehumidify the crawlspace as well. Hence the reason why I added the HEPA filter, fan and dehumidifier into the crawlspace. Since the basement had a major mold issue before, I'm hesitant to try it again. Granted, the entire basement was gutted down to the studs. The only thing that was not emptied was the crawlspace as there was nothing to take out. There was no visible mold anywhere; even on the cardboards, so the room was left alone. The basement, however, looked like a forrest. Everything, and I mean everything was torn down. It was a nightmare. The mold did not reach the other side of the drywall though; which was a good thing. But yes, the basement, which is about 3000 sq. feet, is a bit hot. If left without a dehumidifier, it gets very humid as well. The only ventilation in the basement is a door to the outside which needs to be closed (animals will walk in). I've installed two ceiling fans which are on 24/7. Since there is no AC, there were two mini AC units installed, however, they are expensive (not very energy efficient) to run. The contractor said there was no way to hook it up to the central AC unit.
 
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Old 06-17-15, 08:34 AM
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Your problem with heat is, using the dehumidifiers. They are essentially self contained ac units where the heat is exhausted into the same space. An air conditioner will do a better job of removing moisture while exhausting the heat outside. With a mini-split you could install an ac head in each space while leaving the compressor outside, no ducts. Not a pro on ac units but some here are.

Unless you can tap into your existing conditioned air you are between a rock and a hard spot. 2 pints a day is not a lot of moisture, so perhaps you could continue to address that with a plastic VB over the concrete floor. But VB have a down side in that the moisture side will gradually increase in moisture level until it matches the moisture in the soil below, it will equalize.

Managing the moisture in a crawl or basement is a normal procedure. Not always cheap, but you have seen the alternative.

Bud
 
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Old 06-17-15, 07:29 PM
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Yes, I actually have two of the Pioneer Ductless Mini Split's in the basement. However, these are expensive to run when compared to the dehumidifiers. Plus, I do not believe the mini-splits would reach inside the crawlspace. I was unable to find any mini splits which are energy star compliant. However, these are the best sellers and highest rated on Amazon. I put them on occasionally. However, I do not have them on 24/7. The dehumidifiers, seem to be on 24/7 though.
 
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Old 06-18-15, 04:13 AM
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The problem seems to be down to which appliance to use and whether the dehumidifiers are cycling properly. Lets see if some of the hvac guys can offer more advice.

If you have mini-splits, you could install a head in that crawlspace. As for cost to operate, from what I know, that should be related to the work it is doing. In other words it should cycle on and off as needed. Turn an air conditioner on in a cold dry room and it should just sit there. Add humidity and some have a setting to address just that. But an ac unit should solve your crawl space problem at a lower operating cost than a dehumidifier.

Airman, others??

Bud
 
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Old 06-18-15, 06:57 AM
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They have ductless splits that are rated at 33 SEER so they will be cheap to operate. I still have to believe that if you put down at least a 6mil vapor barrier on the floor and the walls of the crawl. Making sure to overlap and seal. That you will not need a dehumidifier in the crawl space. I have only seen just a few that would still need a dehumidifier. One issue with AC in a cooler basement is sometimes it has to run temps down into the 50's to run long enough to remove the humidity.
 
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Old 06-18-15, 02:01 PM
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The ones installed are 15 SEER (two of them). The crawl space is pretty dry now pulling in nearly a few pints a day, if that. However, the dehumidifier never shuts off. It's set at 40. Should I enable the timer mode, or would that work against me? I will also be purchasing the vapor material so that I can also add that to the walls and most of the floor (one small section will need to be open. No way around it.)
 
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