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Old 07-21-2008, 03:57 PM   #1
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dehumidifier INSTEAD of crawl space vents


hi everyone!
does anyone know if i can install a dehumidifier INSTEAD of crawl space vents? I have my architect/engineer telling me he would not advise them in this area and to close them after i install them! seems a lot of work if i can just have a dehumidifier with a humidistat. anyone?

tnkx!

DM

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Old 07-21-2008, 05:40 PM   #2
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dehumidifier INSTEAD of crawl space vents


Many localities require vents as code. I would ask your local building department about an exception, but I doubt you will get it. The code is for the building, not you per se. The next person that owns the house won't put a dehumidifier in there and moisture issues will arise.
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Old 07-21-2008, 08:37 PM   #3
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dehumidifier INSTEAD of crawl space vents


Ron is right. The code requires vents in a crawlspace unless a number of conditions are met. If there is HVAC ran to the crawlspace, vapor barrier, etc, then that might help you eliminate the vents.

As an inspector, I would not consider the installation of a dehumidifier in trade for no ventilation.
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Old 07-22-2008, 08:32 PM   #4
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dehumidifier INSTEAD of crawl space vents


In my area, it was found through studies that moisture, did in fact come in through the vents in humid air.
My house has a 3 foot crawl space with the earth covered with a 6 mil poly. vapor barrier.
I closed off the vents about 10 years ago and this area has become drier than the Sahara desert.
Its important to keep this area completely sealed off from any outside, humid air.
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Old 07-22-2008, 09:05 PM   #5
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dehumidifier INSTEAD of crawl space vents


Quote:
Originally Posted by Wildie View Post
In my area, it was found through studies that moisture, did in fact come in through the vents in humid air.
My house has a 3 foot crawl space with the earth covered with a 6 mil poly. vapor barrier.
I closed off the vents about 10 years ago and this area has become drier than the Sahara desert.
Its important to keep this area completely sealed off from any outside, humid air.
What is being described here is not a code-legal installation. The vents can be eliminated if a vapor barrier is installed, but the area has to have pass-through ventilation to the house or HVAC running into it.

Site-specific conditions will definately vary from region to region, and from house to house on the same block, as Wildie has demonstrated. There's some risk in doing what he's describing, in that moisture may still find its way in and lack of ventilation will result in excessively humid conditions. Goes to show that it works for some peoples' homes though!
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Old 07-23-2008, 07:56 AM   #6
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dehumidifier INSTEAD of crawl space vents


They have wireless weather monitors you can place in the crawl space to monitor both temperature and humidity. You put the base station where you can monitor it and put the remote units where you want. I have one in each crawl space for this purpose.
I also close off the vents in winter to keep the pipes to the kitchen from freezing. Now that the plumbing inspection is done, I can reroute the water lines to a less idiotic location.
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Old 07-23-2008, 08:02 AM   #7
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dehumidifier INSTEAD of crawl space vents


Vents is old school. See buildingscience.com. If your crawlspace is colder than the outside and you have vents, the relative humidity of the air will increase as it comes in from the vents, possibly leading to mold growth. Seal all air coming from the outside, put 6 mil plastic over the floor & use a dehumidifier. If it is a large space, the biggest residential dehumidifiers are from ThermaStor
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Old 07-24-2008, 11:56 AM   #8
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Originally Posted by thekctermite View Post
What is being described here is not a code-legal installation. The vents can be eliminated if a vapor barrier is installed, but the area has to have pass-through ventilation to the house or HVAC running into it.

Site-specific conditions will definately vary from region to region, and from house to house on the same block, as Wildie has demonstrated. There's some risk in doing what he's describing, in that moisture may still find its way in and lack of ventilation will result in excessively humid conditions. Goes to show that it works for some peoples' homes though!
In my case, the crawl space is in fact, now conditioned!
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Old 07-24-2008, 01:09 PM   #9
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dehumidifier INSTEAD of crawl space vents


In order to be considered conditioned, there would have to be duct openings in the crawlspace or the crawlspace must open into the condtioned basement.

Vents are not "old school", and are routinely installed in crawl spaces, as required. There are certainly better ways of doing it, but you can't just close them off and not take steps to get air circulaiting in there.
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Old 07-26-2008, 08:29 PM   #10
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dehumidifier INSTEAD of crawl space vents


Quote:
Originally Posted by PerpetuallyRepairing View Post
Vents is old school
Maybe so, but they are still required by most of the codes, so I would talk to the local building dept before spending any money on dehumidifiers and humidistats.

Last edited by troubleseeker; 07-26-2008 at 08:37 PM.
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Old 07-27-2008, 08:21 AM   #11
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dehumidifier INSTEAD of crawl space vents


Quote:
Originally Posted by PerpetuallyRepairing View Post
Vents is old school. See buildingscience.com. If your crawlspace is colder than the outside and you have vents, the relative humidity of the air will increase as it comes in from the vents, possibly leading to mold growth. Seal all air coming from the outside, put 6 mil plastic over the floor & use a dehumidifier. If it is a large space, the biggest residential dehumidifiers are from ThermaStor
- I love when people, who read about this stuff online, poo-poo everything the: Codes Guys, and the Builders/Remodelers have to say (When they are the ones actually in the field, working with designers & engineers, constructing, inspecting, testing, monitoring, & repairing these structures).

It's like somebody reading online, an article about how to repair one part of an engine, and dismissing what actual experienced mechanics (the trained guys who work on engines everyday) have to say...

Last edited by AtlanticWBConst.; 07-27-2008 at 08:37 AM.
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Old 07-27-2008, 11:43 AM   #12
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dehumidifier INSTEAD of crawl space vents


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Originally Posted by AtlanticWBConst. View Post
- I love when people, who read about this stuff online, poo-poo everything the: Codes Guys, and the Builders/Remodelers have to say (When they are the ones actually in the field, working with designers & engineers, constructing, inspecting, testing, monitoring, & repairing these structures).

It's like somebody reading online, an article about how to repair one part of an engine, and dismissing what actual experienced mechanics (the trained guys who work on engines everyday) have to say...
Building practices do change and venting in my area is not done anymore, as it leads mold growth from the humidity, whose source is from the vents.
It like using fuel injectors instead of carburettors.
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Old 07-27-2008, 12:22 PM   #13
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dehumidifier INSTEAD of crawl space vents


Quote:
Originally Posted by Wildie View Post
Building practices do change and venting in my area is not done anymore, as it leads mold growth from the humidity, whose source is from the vents.
It like using fuel injectors instead of carburettors.
Am am sorry, but that's actually a very vague statement: "It's not done..."

What exactly does that mean?

... It's not in in your Building Construction Code Books as a requirement anymore? Your local building dept allows/doesn't allow this? Your local inspector doesn't think it's important, or doesn't care, or doesn't know? It's not required by code enforcement for permit approvals and CO's (City/town's opinion, county opinion, state opinions?). Engineers and Architects no longer include them as part of their design plans?...?

FWIW: Cross-Venting of crawl spaces, is currently required, by construction code in my area (it's in the code books). IMHO - it makes perfect sense in building design and regional climate needs.

Last edited by AtlanticWBConst.; 07-27-2008 at 12:37 PM.
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Old 07-27-2008, 12:39 PM   #14
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dehumidifier INSTEAD of crawl space vents


Quote:
Originally Posted by Wildie View Post
Building practices do change and venting in my area is not done anymore, as it leads mold growth from the humidity, whose source is from the vents.
It like using fuel injectors instead of carburettors.
How do you know that it is not done in your area? Are you a builder? A remodeler? An inspector? Your area must be somehow different from the rest of the United States, where vents are still required by the International Residential Code, for good reason.

Your thinking is flawed if you think that a crawlspace won't mold without some sort of ventilation. You stated that your own crawlspace is now conditioned space, so I assume that you ran HVAC to it. With a vapor barrier on the floor and no vents, that is the thing to do, so you did it right. However, for someone that doesn't install a vapor barrier on the ground and doesn't have HVAC running to the space, vents are an asset. Without them, I guarantee that they'll get mold.

People need the whole picture in order to make an educated decision, and it is nothing short of irresponsible to state that vents are old technology (and recommend against them) without fully explaining how you came to what I hope is an informed decision, and how that practice can be substantiated by code. Fact is that they are required in many instances, therefore I find it irresponsible to state that they are not necessary.

The OP may be pouring their foundation and either installing blockouts in the concrete for vents or not based on what they're told here. I think we all owe them fact and not opinion, because installation of vents as an afterthought can be a challenge with some designs. MdangermouseM, you also need to know that the vents must not be operable per the IRC code, as your architect suggested. I don't like that, but that is the way it is. They have to remain open year-round. Insulation would be in order to keep the adjoining spaces warm in the winter and cool in the summer.
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Old 07-27-2008, 01:28 PM   #15
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dehumidifier INSTEAD of crawl space vents


wow, now i'm more confused than before! in the Crawlspace-to vent or not to vent thread that tomandlu started, AtlanticWBconst. showed some great ideas he did that the windows and vents DO open and close, i certainly cannot fathom allowing ice cold air to circulate under my feet freezing my floors and pipes! where is the sense in that since winter weather is usually quite dry! MANOMAN, I'M STUCK ON THIS ONE! someone shoot me please.

DM

PS AtlanticWB, if you read this, where can i get those awning-style vinyl basement windows you showed, how do they open, from the outside? and will they satisfy my codes inspector? tnkx!

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