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Fairfield, NJ on Sep 24, 2011

I have forced air for my furnace and central air conditioning.

I recently noticed that sometimes the duct work is "sweating". This duct work is located in the garage (duct in garage is insultated) and laundry room (unit is also located in laundry room)....What's wrong? What should I do? Will the duct work rust? Please advise. Thank you.

4 Comments

James A Roswell, GA

The duct sweats because its outside surface is below the dew point of the air surrounding it, or the humidity is high. Might increase the air flow. Maybe a louvred door for the laundry room. Perhaps sealing and insulating garage vents.

on Sep 25, 2011 · Like 0
Emperor cooling and heati... Covington, GA

Also the insulation on the duct may not be enough. I am assuming the duct work is metal and alot of the metal duct work is older so insulation standards weren't what they are today. If it's that old aluminum foil looking stuff then I would suggest re wrapping these ducts . Hope this helps.

on Sep 25, 2011 · Like 0
Woodbridge Environmental ... Colonia, NJ

Both folks are correct on this, but a few other things can also be wrong.
The ducts should be wrapped with a foil faced duct wrap, not house insulation. The foil facing should be sealed tight with no holes or tears. The reason for the foil is to prevent any moisture from reaching as James stated to the colder ducts and condense . The inch thick insulation in our region of the country is more then enough thickness to prevent the cold duct temps from reaching the ...»
surface of the foil causing condensation to form on outside of facing.
If this is indeed happening, then I would check into the operation of the
AC system as chances are your air flow is too slow, causing the air temps leaving the evaporator coil located on top of the furnace to be much colder then it should.
If the foil barrier is torn or damaged then I suggest that the insulation be replaced.
Excessive moisture will rust ducts, but the bigger issue is mold development on the insulation or any surfaces that the ducts may come into contact with that will promote microbial development once damp from condensate.
Feel free to contact me to discuss this further if you like. My number is on my profile page.
Bob

on Sep 26, 2011 · Like 1
HandyANDY Home Renovation... Marietta, GA

It couldnt be put any better. Give Bob a call. We see alot of this in older homes in Atlanta where there was initially only central heat. Years later, someone comes along and adds air but doesn't properly insulate the supply lines or the register boxes. I'll post a pic later with the black mold outlines coming through the wall in one client's home. Mold and mildew is a much more serious issue in our market.

on Sep 26, 2011 · Like 1