Supply side ductwork in crawl space sweating

[dkeener]

Hi Folks.. I have a question. Its been a very wet and humid late June and early July here in central NC. I noticed that the 'stand up' crawl space was quite wet and found that the water was coming from the sheet metal supply plenums and the flex ducts. They were all sweating bullets. The system is a Carrier 48XT Infinity dual fuel with 2 speed compressor so its running quite a bit dehumidifying. I tried drying the ducts off and running a fan in the crawl space which made little difference. I then discovered that the condensate drain was plugged. Could the plugged drain explain the sweating issue? Could the excess water be getting picked up by the fan and blown thru the supply ducts? Condensate did seem to be exiting the system around the base of the unit. The drain is now fixed and Ill be watching what happens under the house.

Thanks!!

[Brent Ridley]

Is the crawlspace encapsulated?

My guess is...No.

When operating with low speed fan, the ducts are below the dew point of the crawlspace; creating condensation on the face of the ductwork.

You need to encapsulate and add a small dehumidifier in your crawlspace. This will prevent any sweating, mold, mildew, and moisture issues from occurring.

[dkeener]

Is the crawlspace encapsulated?

My guess is...No.

When operating with low speed fan, the ducts are below the dew point of the crawlspace; creating condensation on the face of the ductwork.

You need to encapsulate and add a small dehumidifier in your crawlspace. This will prevent any sweating, mold, mildew, and moisture issues from occurring.

No. The crawl is just open with multiple foundation vents and no insulation.

Ive never seen this much sweating in all the years of having this system.

Perhaps If I turn off overcooling for humidity control (set it back to efficiency mode)?

[Brent Ridley]

Perhaps If I turn off overcooling for humidity control (set it back to efficiency mode)?

This will help but may not completely remedy the situation.

[Southern Mech]

Close your vents and get a dehum unit to put under there. Make sure the dirt is covered wall to wall.

I am having this same issue at a cistomers house. After he has blamed me for the issue he opened hi s vents 2 weeks ago that have been closed for 6 years. He had water dripping off the floor joists in 2 days. He also has a grade problem.

[dkeener]

Hmm.. Close the vents? I always thoughts those vents were to be wide open year round?

[Southern Mech]

That's old way of thinking...that code officials, dept of insurance and of the like are starting to see is not a good idea. Cold air settles through the floor and into the crawl. When it does it is met by hot humid ou tside air via crawl vents. Now you basically have a thunderstorm brewing. Colder and less humid house =worse conditions get.

[dkeener]

Interesting... I see your point. I will try closing the vents.

[dkeener]

I changed the A/C airflow setting in the Infinity control to 'efficiency' instead of 'comfort' and the duct sweating reduced dramatically. Hopefully that will be all that is needed.

Thanks!