https://www.energyvanguard.com/blog/case-closed-get-those-air-conditioning-ducts-out-of-the-attic/ Building science knowledge, HVAC design, & fun Tue, 28 Jun 2022 12:06:02 +0000 hourly 1 https://wordpress.org/?v=6.6.2 https://www.energyvanguard.com/blog/case-closed-get-those-air-conditioning-ducts-out-of-the-attic/#comment-2049 Sat, 18 Oct 2014 02:27:30 +0000 http://energyvanguard.flywheelsites.com/?blog_post=case-closed-get-those-air-conditioning-ducts-out-of-the-attic#comment-2049 @Ira, it is not a good idea
@Ira, it is not a good idea to close a crawlspace (in a humid climate) that wasn’t designed that way. In particular, there must be a continuous vapor retarder on the exterior walls and ground. Trying to dehumidify a non sealed crawl would be an exercise in futility.  
 
Since this is a vented crawlspace, condensation can easily be eliminated by properly insulating supply ducts with a product that has a continuous vapor barrier on the outside, with complete coverage of boots and every cold metal surface, and all joints taped. As long as moist air can’t reach cold metal, there’s no possibility of condensation. The air handler itself has internal insulation on the supply side to avoid this problem.  
 
If you have a wet crawl floor, you should address the source (roof and site drainage away from foundation, and/or sump pump at low point if water is coming from ground within the crawl. But that has nothing to do with wet ducts. In a humid climate, uninsulated ducts in a vented will always sweat, and properly insulated ducts will not sweat.

]]> https://www.energyvanguard.com/blog/case-closed-get-those-air-conditioning-ducts-out-of-the-attic/#comment-2048 Fri, 17 Oct 2014 16:16:18 +0000 http://energyvanguard.flywheelsites.com/?blog_post=case-closed-get-those-air-conditioning-ducts-out-of-the-attic#comment-2048 Jeremy… 

Jeremy… 
You are saying that your floors are wet from condensation from the air vents, and the joists are rotted where the vents touch them. Do you mean the vents that actually blow air into the room, or the ducts that run through the crawlspace and are fastened to the joists? 
 
If it is the actual vents, then you have a bigger problem, but the solution is the same regardless of whether it is the vents or the ducts that are making the condensation. 
 
If it is the vents, you can’t lower those or make them not touch the floor or joists because they stick through the floor and blow air into the room. 
 
Assuming it is the ducts, the short answer is that you can lower them so they don’t touch any wood. That will not stop the condensation though. 
Doing that will allow you to put insulation on the ductwork which will result in less condensation. Its a good idea for energy efficiency too. 
 
The real source of your problem is too much humidity in the crawlspace. That can be from several causes. The most common is that crawlspace vents are commonly left open during the summer, and warm humid air comes into the crawlspace. The cold air blowing through the vents then condenses the humidity into water which rots your wood.  
 
Keeping your crawlspace vents closed is the simplest solution, and will most likely solve that problem. 
 
You may have a high water table in your area and moisture is getting in through the walls or floor of the crawlspace.  
 
If that is the case, you may need to put a dehumidifier in the crawlspace (that drains into a sump pump) to lower the humidity. You can also have one or two vents put into the ductwork to blow air conditioned air into the crawlspace which will lower the humidity, but remember to shut those in the winter so you don’t waste heat, and remember to open them again the next summer.

]]> https://www.energyvanguard.com/blog/case-closed-get-those-air-conditioning-ducts-out-of-the-attic/#comment-2047 Thu, 16 Oct 2014 17:25:18 +0000 http://energyvanguard.flywheelsites.com/?blog_post=case-closed-get-those-air-conditioning-ducts-out-of-the-attic#comment-2047 I have my duct work in the
I have my duct work in the crawlspace of my home its about a 4ft crawl. Here is my problem. My floors have soaked the moister from the condensation of air vent that now it has rotten my joist where the vent touched them and subfloors are as well. My home is 20 yrs old. is this normal? should I have the ducts lowered away from joist a few inches?

]]> https://www.energyvanguard.com/blog/case-closed-get-those-air-conditioning-ducts-out-of-the-attic/#comment-2046 Wed, 03 Sep 2014 22:05:20 +0000 http://energyvanguard.flywheelsites.com/?blog_post=case-closed-get-those-air-conditioning-ducts-out-of-the-attic#comment-2046 I have been saying this very
I have been saying this very thing for years. The books that I learned from stated that in general terms that the systems size had to be increased 1/2 ton for every 100sqft of exposed duct in an unconditioned space, that is both supply and return.

]]> https://www.energyvanguard.com/blog/case-closed-get-those-air-conditioning-ducts-out-of-the-attic/#comment-2045 Tue, 19 Aug 2014 17:06:58 +0000 http://energyvanguard.flywheelsites.com/?blog_post=case-closed-get-those-air-conditioning-ducts-out-of-the-attic#comment-2045 M. Johnson
M. Johnson: I talk to a lot of people who know a whole lot about what’s going on in the industry, and that’s the first time I’ve heard about this lawsuit. Doesn’t mean it didn’t happen. I just think I’d have heard something if it did.  
 
I addressed the roof rot issue in a previous article: 
 
Will Open-Cell Spray Foam Insulation Really Rot Your Roof? 
 
That would be a better place to post your comment.

]]> https://www.energyvanguard.com/blog/case-closed-get-those-air-conditioning-ducts-out-of-the-attic/#comment-2044 Tue, 19 Aug 2014 16:49:47 +0000 http://energyvanguard.flywheelsites.com/?blog_post=case-closed-get-those-air-conditioning-ducts-out-of-the-attic#comment-2044 I am told there was a class
I am told there was a class action lawsuit involving 260 plaintiffs, involving a major builder who had many roof deck failures using foam at the roof line in a hot-humid climate. And that the settlement included a requirement that the plaintiffs not discuss the matter. I do know Pulte Homes built with this design at one time in Cinco Ranch (Houston TX), and will not build that way today. Wish I could cite some good references, but hearsay is just about all I have. But this hearsay comes from pretty good people. 
 
For someone learning building science, it is maddening to hear of evidence being suppressed. If someone could inform us what must be done to prevent such roof failures, that would go a long way toward settling these uncertainties in my mind.

]]> https://www.energyvanguard.com/blog/case-closed-get-those-air-conditioning-ducts-out-of-the-attic/#comment-2043 Tue, 19 Aug 2014 10:39:32 +0000 http://energyvanguard.flywheelsites.com/?blog_post=case-closed-get-those-air-conditioning-ducts-out-of-the-attic#comment-2043 @Brandon, if ducts are
@Brandon, if ducts are original, they’re unlikely to be sealed. Metal ducts are naturally very leaky. This isn’t just an efficiency hit. Leaks on the return side will draw air from the crawl which is often humid and worse.  
 
There are a couple of ways to seal existing metal ducts… spray sealant (Aeroseal) on the entire interior surface, or brush on mastic along the seams from the outside (requires removal of insulation wrap).  
 
Either way, sealing in-place metal ducts can be an expensive proposition. You might want to investigate the cost of encapsulating the attic as an alternative to moving the system.  
 
But first, you should contact the previous owner or the installing contractor to find out why the crawl duct system was abandoned.

]]> https://www.energyvanguard.com/blog/case-closed-get-those-air-conditioning-ducts-out-of-the-attic/#comment-2042 Tue, 19 Aug 2014 07:15:42 +0000 http://energyvanguard.flywheelsites.com/?blog_post=case-closed-get-those-air-conditioning-ducts-out-of-the-attic#comment-2042 Spraying closed cell foam on
Spraying closed cell foam on ducts will not release anything when the ducts are carrying hot air. 
Once the foam “cures”, it doesn’t release anything unless you take a blow torch to it.

]]> https://www.energyvanguard.com/blog/case-closed-get-those-air-conditioning-ducts-out-of-the-attic/#comment-2041 Tue, 19 Aug 2014 04:05:09 +0000 http://energyvanguard.flywheelsites.com/?blog_post=case-closed-get-those-air-conditioning-ducts-out-of-the-attic#comment-2041 @ the person from St.
@ the person from St. Augustine, Fla. who wants to spray closed cell foam on the ducts…Why? Its a band-aid approach. Granted, its a cooling climate , I assume, although heat run through the ducts at any time might release isocyanates into the home, whats a better choice you ask; build a frame within the envelope where you could to hold the ductwork…thats the best approach, or get a new builder!

]]> https://www.energyvanguard.com/blog/case-closed-get-those-air-conditioning-ducts-out-of-the-attic/#comment-2040 Tue, 19 Aug 2014 00:57:29 +0000 http://energyvanguard.flywheelsites.com/?blog_post=case-closed-get-those-air-conditioning-ducts-out-of-the-attic#comment-2040 We just purchased a 1955
We just purchased a 1955 ranch-style home here in Dallas. The house is single-story and has a 3-5 ft crawlspace underneath. The prior owner just had a new AC system installed in which they switched from the equipment and metal ducts in the crawlspace to flex ductwork/equipment in the attic (where temps have regularly been in the 130-150 degrees this summer). The old ductwork and vents are all still in place, and in good shape (even insulated). The new system does not seem particularly efficient. My wife and I were considering having the ac system moved back to the crawlspace. We owned another home with old crawlspace ductwork in place that had been abandoned in favor of attic flexduct, so this isn’t our first time looking at this. Any info? Thank you for the great blog.

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