Return to the Heating & Air Conditioning Forum | Post a Follow-Up

AC plenum in crawlspace sweating?

Posted by Alberich (My Page) on
Sun, Jul 15, 12 at 18:59

I had a brand new Trane ac and plenum installed last summer in my crawlspace, and to date it has been a nightmare dealing with a poor install. The (national) company who sold and installed the unit has already been out 7 times to "fix" issues. Last time, they took almost everything apart, put it all back together with new insulation and parts, and sealed everything with mastic "goop" and tape. The air in the house is now finally cool and dry--so it feels like they (finally) got the job right.

However, one week later I just discovered that water is puddling on the outside of the insulated sheet metal plenum and dripping off the connections to the ducts. I can't tell if it's happening on the inside too . . .

I live in the southeast, and the weather is hot and humid. However, it's only been in the upper 80's this past week. The crawlspace under the brick house is on a slope ranging from 7 to 4 feet in height and is not insulated. There are 8 vents in the brick that we open in the summer and close in the winter, and there is a sheet of plastic ~4mm thick on the floor.

We didn't seem to have this issue before with the previous AC, which was made out of duct-board.

Can anybody please tell me what is going on, how this issue can and should be fixed?

Follow-Up Postings:

RE: AC plenum in crawlspace sweating?

If the metal plenum is sweating, then there is an insulation problem. They might have used just a sheet metal plenum with out any internal which case they should have wrapped it on the outside. I would take some pictures and give the installing company a call.

Hope this helps

RE: AC plenum in crawlspace sweating?

Thanks for your reply, but they did cover the outside of the plenum with insulation. Therefore, the water/condensation is collecting on the outside of the insulation. What can I do about that, and how would I know if there was moisture underneath the insulation as well?

RE: AC plenum in crawlspace sweating?

It seems likely to me the problem may be excessive moisture in your crawlspace. If the crawlspace is vented as most are, consider that you have hot humid air surrounding the outside of the building. Now you bring that humid air into the crawlspace where it is nice and cool..The humid outside air reaches saturation point in the crawlspace and anything just slighly cooler like you ductwork is going to sweat. Check the humidity in your crawlspace. Solution could be sealing the crawlspace to installing a dehumidifier. I believe that the the latest trend in new crawlspace construction is to seal and insulate them to prevent moisture and mold problems.

RE: AC plenum in crawlspace sweating?

Consider the possibility that outside air is leaking past poorly-installed insulation and water is condensing on the duct. That wets the insulation rendering it useless so you get condensation on the outside vapor barrier.

 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!

Return to the Heating & Air Conditioning Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Please review our Rules of Play before posting.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.

Learn more about in-text links on this page here