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Why is My Ductwork Sweating

I recently received a great question on one of our crawl space encapsulation posts:

Hi! I am in the process of encapsulating my crawl space and when checking the insulation around the duct work, it is completely soaked. Do I need to replace the insulation over the duct work or can I remove all duct work and leave the ducts non-insulated?

If you'd like to read the article:

Crawl Space Encapsulation Questions


It is a great question that many homeowners ask dealing with improving the indoor air quality of the home. Sweating ductwork can affect the home by causing humidity to increase and saturate whatever space the ducts are located. Not to mention humid air being passed to all parts of the home via the ducts.

The Ductwork Sweating Problem

My answer to the homeowner was to address the root cause of the problem. I feel many people only look at fixing the symptom of sweating ducts. She asked if she should remove insulation, which seems logical, but that will not stop the ducts from sweating.

The ducts are sweating because of high humidity in most cases. Leaky ductwork will make the problem even worse. The more cold are escapes the ducts and hits the warm air in the crawl space, the more the ductwork sweats.

image of ductwork sweating

Should I Remove Duct Insulation

The only reason to remove the insulation is if it is moldy or really damaged, but removal should not be permanent. Removing the insulation will expose the cold ducts even more; fixing the humidity problem will solve the issue.

If you remove the insulation, replace it after you air seal the ductwork. This will make sure the cool or warm air produced by your HVAC system is taken to the areas intended. In the winter, ductwork without insulation

Will a Dehumidifier Stop Sweating Ductwork

The number one question we receive on our YouTube Channel and comments is "Do I need a dehumidifier?" If you are a DIYer or looking for someone to fix the humidity problem in your attic, basement, crawl space, or whole home, the dehumidifier is the best solution.

Do you need help fixing a humidity problem or ductwork sweating in your home? Please click here to contact us. Also make sure you check out the video below and please leave us a comment on what you have done to improve your home's energy efficiency.

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About Michael Church

Michael Church has been involved with indoor air quality since 2005 and feels the unhealthy crawl space is one of the major problems causing poor indoor air quality.


  1. George on September 5, 2020 at 4:41 pm

    Great channel! I have a newer home and am considering installing a dehumidifier in the crawl space. ( seems humid, duct work causes condensation which drops onto the crawlspace floor which is covered in plastic). My question is: Do I need to encapsulate for the dehumidifier to work properly? I was going to seal the vents ( saw your video on that ).

    • Michael Church on September 9, 2020 at 11:52 am

      Great question George. I think installing a dehumidifier and sealing the vents is a great step in correcting the condensation problem you face. Just keep in mind that the better the ground is covered and the less hot humid air infiltrates the crawl space, the less the dehumidifier will run. If you install a small dehumidifier with very little power, it may not keep up. The 1820 by Aprilaire is great but if your ground is exposed and the wood moisture level is high, it may not keep up either if your crawl space is fairly large. This would mean you should step up to 1850 or 1870 to make up for the encapsulation not being installed. I hope that helps. Here is a link to our dehumidifiers if you want to read more about their specs: https://diy.crawlspaceninja.com/product-category/dehumidifiers/

  2. Matthew Lariviere on March 2, 2022 at 8:24 pm

    I recently hired a mason to brick up the vent holes and “anywhere you can see light coming in.” It worked awesome. RH holding 35-40% only 12 hours later. Home was built in 74. Now I notice a dirty sock smell coming from the vents when the AC comes on and I think its the old duct insulation probably soaked in mold from 40 years of humidity. My HVAC unit is 2 years old, MERV-11 at the unit, changed every 3-6 months.

    I currently have a 70 pint basement dehu hacked under there with a pump with plans to swap it out for the 1830. Already a dedicated circuit from the old HVAC humidifier.

    Do I have the right idea to finish it off by getting a powder coated steel insulated crawl door from grainger, remove the duct insulation permanently and mastic paste all the duct joints to finish the job?

    That would leave me at hiring someone to pull the old vapor barrier out and rewrapping 1200sqft. Ive been quoted anywhere from 6-12k for just a rewrap.. doesnt sound right.

    Is my plan a good plan and whats a reasonable cost to just wrap floor, walls and pillars?

    To top it off I put a smartthings multisensor in there to keep tabs on light levels, motion (rodents), and RH. Very effective.

    Burlington, NC

    • Michael Church on March 5, 2022 at 10:12 am

      Hi Matt, properly installed vapor barriers for walls, pillars and floor can cost more than most expect due to the labor element of doing it correctly and the company standing behind the warranty. Be sure to get several estimates and compare company reputation would be my suggestion. I like the removing duct insulation and mastic but I would also reinsulate if your local code requires it. If it was my house, I would anyway to create a thermal break between ducted air temp and crawl space temp even if not required by code. Hope that helps. Thank you.

  3. Tanner stenger on August 8, 2022 at 12:11 pm

    My floor is wet at the vents under the house not inside the home…very sweaty ac ducts

    • Michael Church on August 10, 2022 at 10:02 am

      Hi Tanner, we see that quite a bit. Normally it is due to cold metal duct boots sweating and leaching water into the subfloor. Do you have a dehumidifier installed under the home? If not, that may help.

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