Condensation on Supply Air Ducts 2

[k29]

Wondering if anyone can help, I have condensation on the supply air ducts in the space between the 2nd and 3rd floor of a townhouse. There is no return air on our heat pump unit, the heat pump is new (1 year old) and the condensation has rotted two layers of ceiling drywall. Should I used insulation on the duct and if so any recommendations on the type?
Thanks.

 

[AEBuck]

The supply duct should have been insulated from the start. Use a fiberglass blanket with foil facing, typically 1.5 to 2 inches thick. Most importantly in your case, the foil facing is meant to function as a vapor barrier, so you will need to use duct tape to seal all joints and prevent moisture in ambient air from reaching the surface of the duct. Install insulation continuously from the discharge of your indoor unit to all supply outlets. There is little variation between insulation products of this type from various manufacturers.

Also most curious is the lack of a return duct? Why did you mention that? Where do you live? Since you'll be opening up walls and ceilings to insulate, I'd really consider having return ductwork installed to reduce your energy bills.

 

[k29]

Thanks for the info, I will try that.
Live in VA, no return air can make it warm here in the summers = cranking the heat pump to cool off the house=condensation on supply air duct, a bad cycle.
Thanks again

 

[quark]

The surface temperature of a foiled insulation will always be lower than that of unfoiled insulation due to high emissivity of the foiling material. When insulation is foiled or cladded, you should supplement it with extra insulation thickness to negate the condensation effect.

If you go with closed cell insulation material, you can reduce the moisture permission and you need not foil it. Any of the insulation manufacturers can do the calculation of insulation thickness with and without cladding and you can plan as per your budget.

For a clear idea go to,

http://www.extolohio.com/DATA/ARTICLES/emittance.html

Regards,