Asked on Jun 12, 2013

Duct work is sweating in the crawl space!

FilterDeliveredCaperniusMike Lee
+7

Answered

Today we installed a door to the part of the crawl space that you can stand in and discovered all of the black coated, insulation wrapped HVAC ductwork is sweating. OK, it was 95 degrees today but this can't be good! Of course we didn't know and have no idea how long it's been going on. So afraid of mold now. What's up? What to do?
10 answers
  • The reason for the sweating is the dampness in the space is cooling down to the dew point on the cold insulation. If you have older insulation you will need to remove and replace with foil faced duct wrap. Not house insulation. You need to purchase the thicker or Higher R value wrap. They make two thicknesses of this product. As far as mold, perhaps there may be some because of the paper wrapping but the stuff needs to be removed. When replacing the insulation you need galvanized wire that comes on small spools Often called baling wire. You also will need foil backed tape, Not duct tape. Get the expensive stuff not the low cost or it will fall off in a few short months. First off remove all the old stuff and wipe the duct down with a damp cloth to remove any dust. Then using the foil tape tape every duct seam to prevent any air leakage out and into the ducts. Then wrap the duct with the insulation then use the foil back tape to seal every opening. Do not let air come into contact with the duct or it will sweat under the insulation causing it to fail in short order. Once you insulate all of the ducts in the space, take the wire and wrap it around the duct to help support the fiberglass from drooping. This will prevent the tape from failing and make the job last a long time. Just remember, no exposed ducts, wrap everything. Do not compress the insulation to much, you need the higher R value to prevent the foil face from cooling down causing the the outside of the insulation to cool down enough to cause the condensation to form. Lastly address the extra humidity in the crawl space. If it is accessible from the basement? Keep the door access open and close off any outside vents. If its only a crawl space, open up any outside vents, and be sure to cover the floor with plastic if any exposed soil is present. Great amounts of moisture can come from the ground. Have any other questions, please ask or contact me!

  • J & J Refrigeration
    on Jun 13, 2013

    Yes it is time to reinsulate with 2" or 3" foil backed insulation (3" would be best). Use a licensed contractor who has done this type of insulation.

  • The link to article below is a link on what to look for when conducting an energy audit for your home. It explains air leaks and duct work insulation. This could you you out with your situation. http://remodelinghomeimprovement.net/Orlando-Remodeling-Home-Improvement-Articles/home-energy-audit/

  • Dan Kradzinski Remodeling
    on Jun 13, 2013

    Was the duct work the only thing that was sweating? Do the doors on the first floor stick or is there a musty smell when the house is closed up for a few days. A dehumidifier maybe needed to take away the excess moisture in the crawl space.

  • Ncn184084
    on Jun 21, 2013

    Thank you all for your help. I'd say just the sweating is the problem. I don't think there is a musty smell usually as I'm very sensitive to that (we have cats and I worry about smells all the time!). Doors don't stick either. We installed auto-opening crawlspace vents a long time ago. Plus, I suppose insulation has improved since the mid-70s too! Looks like we have our work cut out for us. Thinking we'll pull out all of the old insulation and duct wrap ourselves to try and save some money. Then someone can investigate the underpinnings of the actual floor before having new insulation installed. Of course I welcome any additional thoughts on this idea. Thanks again!

  • Ncn184084
    on Jun 21, 2013

    Thank you all for your help. I'd say just the sweating is the problem. I don't think there is a musty smell usually as I'm very sensitive to that (we have cats and I worry about smells all the time!). Doors don't stick either. We installed auto-opening crawlspace vents a long time ago. Plus, I suppose insulation has improved since the mid-70s too! Looks like we have our work cut out for us. Thinking we'll pull out all of the old insulation and duct wrap ourselves to try and save some money. Then someone can investigate the underpinnings of the actual floor before having new insulation installed. Of course I welcome any additional thoughts on this idea. Thanks again!

  • The Air Conditioning Guy
    on Jul 3, 2013

    The answers I read above about re insulating your ducts should work if they are hard pipe ducts. Usually ducts will sweat because the insulation is not enough or not there. If they are flexible ducts you're better of replacing them. It would be a nightmare trying to insulate them. Are you sure these are air conditioning ducts and not swamp cooler ducts? Even the lower 'R' rated ducts wont sweat. I think you just need to replace the ducts. The reason I say this is because I once saw someone install air conditioning to swamp cooler ducts. These ducts where just like a hose when the system was off they would flatten out just like a fire hose. They will sweat just like a soda can does when you take it out of the refrigerator and put it on a table. The cold condenses the water that is in the air. Hope this helps.

  • Mike Lee
    on Jul 8, 2013

    Wrapping ductwork/ best way is to remove as was stated in above post : to measure easy take size of pipe 6" round =6x2+2 -14" make a mark 14" across the 48" long roll and cut. Then flip and cut-2" off the end of insulation only leave a flap. Then wrap pipe 48" down and start again.

  • Capernius
    on May 3, 2015

    If there is any mold/mildew, experience has taught me That spraying it with straight Vinegar will dispose of it in very short order...

  • FilterDelivered
    on Jun 12, 2015

    you may want to lay down thick plastic if it has a dirt floor as well. also, with any hvac system it is critical to keep air moving at the right velocity and volume, and typically the furnace filter is the culprit of insufficient airflow. BE SURE TO REPLACE YOUR FURNACE FILTER REGULARLY!! Once it's plugged up it restricts air and the ac outlet temp drops and causes even more sweaty ducts. If you can't remember to replace your filter on a consistent basis just go to www.filterdelivered.com and subscribe to have your replacement filter automatically delivered to your door on a consistent schedule. No more remembering! good luck with the moisture issues.

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