Crawlspace dehumidifiers <--- any insights? (floor, roof shingles, foundation, windows)
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I am in the market for a dehumidifier for my new home crawlspace. I am interested in hearing whether any of you currently have one installed, which brand, if it works to low temps and anyother insights or advice. One builder I spoke to says he now regularly installs them standard, after sealing up all the vents. I have read though that most are not rated to work below 50 degrees or so. I do believe the crawlspace may get colder than that during winter.
Unless you have a completely sealed crawlspace, putting a dehumidifier there would be like putting a dehumidifier in your attic space. Not effective. If your crawlspace is completely sealed, then that's another story.
Also, you can go to "askthebuilder.com" and see what's said there. Every crawlspace should have a vapor barrier though.
I'm doing research on the same subject and found out that an attic fan will pull "bad" air from the crawlspace up through the main living area of a home, and also pull humid air through the windows into the living area during the summer.
I've shut my attic fan down in the summertime and find my house is much less humid. Here's a good site about that, too: Advanced Energy
Having lived in humid climates with both a crawl and a slab foundation, I'm still confused about it, although living on a crawlspace, which is further above ground level than a slab foundation is, feels much better to me. I felt like I was walking around on a cement patio when I lived in a house built on a slab.
Just google "dehumidifying a crawlspace" and there's lots of stuff there.
They will ice up if the temp gets too cold. I had to get one that worked to 50 deg for my basement because a regular one iced up in the winter in my 55 deg. basement.
^^^ These are supposed to be some of the best dehumidifers out there. Pricey, but they are very efficient and durable, and definately go down to colder temps.
Different options to choose from. You may even want to consider an in duct dehumidifier, if applicable. Good luck.
I'm doing research on the same subject and found out that an attic fan will pull "bad" air from the crawlspace up through the main living area of a home, and also pull humid air through the windows into the living area during the summer.
I've shut my attic fan down in the summertime and find my house is much less humid. Here's a good site about that, too: Advanced Energy
toodie
I remember this article from a couple of years ago. Though the study was comprehensive and had positive results- the end of the article said it all- you'll have a hard time convincing others; i.e., state, county, and municipal building inspectors. And unless the building code changes for a particular area/city (like NC)- you would have to do it on your own. Then you would be subject to a private inspection if you were to sell (and buyer hired inspector).
As far as the attic fan (we are talking attic ventilation fan)- I believe you're doing more harm than good. Unless your home is 80+yrs old, I doubt it is balloon framed. These fans don't draw a lot energy. But, I'm sure your A/C is drawing a lot more because of the attic fan being off. And if you think your attic fan was drawing that much moisture into your home, I'd check your doors and windows weatherstripping plus seal material for your attic access. Plus, the lack of ventilation really is determental to the roof material- unless its clay tile.
KLedgeBldr,
I'm interested in this subject and thank you for your reply. I hope it's okay to copy and paste this article here, but if you have an opinion about what it says, please pass it on. This is a confusing topic for me but I do know that my a/c bill was lower with the attic fan off; the humidity level was lower and I liked it better without the fan running.
Q: A house we've looked at has extra attic ventilation. In addition to the regular gable-end vents, it has soffit and ridge vents and two power ventilation fans. The builder says that this will help keep the attic cooler in summer, reduce the air conditioning bills, and make the roof shingles last longer. My friend Lou, who's from the old school (still doesn't own a microwave), says it's all a bunch of hype — houses have lasted for hundreds of years without that stuff. Why do we need it now?
A: The fact that houses didn't have certain things for hundreds of years would be a good reason not to do something if we were building houses the same way we built them hundreds of years ago. But we're not building them the same way. Houses today are tighter, better insulated, heated and cooled, wired, and filled with a chemical stew of substances that didn't even exist 100 years ago. So, if we look at Lou's logic, I'd have to say Lou is all wet or, more appropriately, full of hot air.
In this case, however, Lou is probably closer to the truth than he realizes. The original purpose of venting the attic was to remove moisture from damp crawl spaces under the house. Years ago, most buildings were "balloon framed," meaning there were lots of direct connections between the crawl space and the attic. Opening some holes up in the attic had the effect of drawing moist air up from the crawl space, and could help dry out the area under the house.
Over the years, a number of other reasons have "evolved" for venting the attic, including reducing air conditioning bills in the summer, reducing attic moisture problems in the winter, and extending shingle life. Interestingly, the amount of ventilation required by most building codes is still the same as it was 50 years ago — when the purpose was to help dry out the basement!
Let's look at the air conditioning issue. Fifty years ago, when we had little or no insulation in the attic, the temperature of the attic had a big impact on the temperature of the house. The attic floor would heat up and act as a big radiator, radiating heat into the house. Insulation slows down the movement of heat from the attic into the ceiling; and the more insulation we have, the slower the heat moves through, and the less the ceiling will act like a radiator.
New houses today are required to have at least R-30 in the attic. If this insulation is installed properly, heat will move through it very slowly, and once the sun goes down, most of the heat will be given off to the outside, unless, of course, you've got air moving between the attic and the house.
One source of this air movement is air leaks — around the pull-down staircase, around and through recessed light fixtures, and around holes drilled for plumbing, wiring, and ductwork. If you have these kinds of leaks, then air that you paid to cool is leaking into the attic, pulling hot, humid air into the house to replace it.
What happens if we have a powerful exhaust fan running in the attic? While the diagrams that come with the fans always show them pulling the air in through the soffit vents or gable-end vents at the other end of the attic, the fact is that the air didn't go to the same schools as the people who drew the diagrams. So, when the fan comes on, it pulls air through the light fixtures, around the attic stairway, and through any other holes available.
The attic is, in fact, cooled by your air-conditioner. And while that attic fan is pulling air out of the house, it is also pulling make-up air into the house from outside or from the crawl space. Some of these attic fans are powerful enough to create a negative pressure in the house. If you have a gas water heater, this negative pressure can cause it to back-draft, putting poisonous combustion gasses into your house instead of up the flue.
The bottom line? Code-required attic ventilation levels are adequate. Putting in extra ventilation is probably a waste of money. Finally, powered attic vent fans are more likely to increase energy bills than to reduce them, and they can create dangerous conditions in your house. A little extra money to really seal the ceiling from the attic will go a long way toward providing comfort and lower bills.
Granted there are truths and tall tales in anything. As mentioned in the question- there were several types of attic ventilation- it was overkill!
Some simple theory- hot air rises. In attics we create convection, as hot air rises it pulls cooler air in from the soffit vents and it discharges through either the gable vents or the ridge vent. Or in some cases through an electric fan (which is in some cases actually "pulling" air in through the soffit vents). In some cases, an attic ventilation fan can pull air from the house itself because of a lack of/ or blocked soffit vents (the negative pressure). But remember, these fans are controlled by a thermostat (so obviously they are not running constantly).
The theory behind the attic fan to me is this- instead of relying solely on convection to cool the attic, have a consistant exchange of cooler air to cool the attic. Thus, reducing the amount of radiant heat penetrating the ceiling, which inturn relieves the work/energy load for A/C. And by keeping the attic cooler you also extend the life of the shingles on the roof.
Unless you have a completely sealed crawlspace, putting a dehumidifier there would be like putting a dehumidifier in your attic space. Not effective. If your crawlspace is completely sealed, then that's another story.
toodie
In reality, all you have to do is close your foundation vents. You don't need a sealed crawl to make a dehumidifier effective. I have done my own case studies on this taking moisture readings of the structural members throughout the seasons before and after having a DH installed. Of course a sealed crawlspace is nice, but a 100% vapor barrier, keeping the vents closed, and having a DH gains 90% of what a completely sealed/conditioned crawl will give you.
At a 10k price tag to retrofit an existing crawl, they can keep the 10% difference lol.
Does anyone have any experience using crawl space ventilation fans? I've researched the benefits of both, and it seems it depends upon where you live. I had a mold expert tell me to use the vent fans to create a vacuum effect in the crawl space, pull the air from the house down, and the moist air f/ the crawl outside.
Which would be better-a vent fan or a dehumidifier?
Most de-humidifiers are not rated for use in a crawlspace. Basements yes, under the house no. Has to do with UL ratings I think.
The debate between sealed or open crawlspaces is quite diverse and even the "experts" can not agree, and each have compelling research and data to support their cases.
The big part of having a sealed crawlspace work is having "conditioned air" flowing through it. That means you have to have a heat/air ducts in there. All of the information I have read about sealed spaces want you to have a poured concrete floor (like making a mini basement) to fully seal the ground moisture from entering the space.
I have been in many crawlspaces that have a vapor barrier and the vents closed. I would say that most if not all of them have fungus and wood rot issues.
Foundation vent fans work pretty well, and in many jurisdictions, the Building Dept's require them if the foundation vents do not meet spacing, number and size required by the code. I have also seem many retro-fits where the crawlspace ventilation is poor, and they are having fungus issues.
I have also seen several houses that had household fans and de-humidifiers in the crawlspace. They were usually a rusted out mess and didn't work. When you put a de-humidifier in a crawlspace, you still have to get rid of the water. probably a pump will be needed.
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crawl space vent fans or a dehumidifier?
