Sweating HVAC Supply Duct

[rgf2912]

I have a 2 story colonial type house with the HVAC ducts that supply the downstairs run in the space between the ceiling/floors, about 2 feet high. The ducts to the kitchen and breakfast area are 8" round flexible uninsulated duct that sweat and stain the ceiling. There is what I would call random batts of insulation in the space but hardly 100% coverage. Would replacing the runs with insulated duct solve this problem? How about blowing in loose insulation? Most of the homes in the neighborhood all suffer from this problem so the contractor messed up. I really don't want to tear down the ceiling if at all possible but would like to have this problem behind me before the upcoming kitchen remodel.

[energy_rater_La]

do you have attic access to the area surrounding the second floor?
you can blow in insulation...but spots will be missed due to ducts/
framing, pipes etc.
foam sealing between the floors would be a better option.
this would seal attic air from moving between floors and then
ducts would truly be in a conditioned space.
best of luck

[rgf2912]

The place where I'm having the problem is between the first floor ceiling and the 2nd level floor, the space created by the floor joists. It's about 24" high, with access only from the registers unless I take down sheetrock on the ceiling of the first floor.

[sktn77a]

Are you sure you have a 24" space between floors (usually, it's more like 12")? If so, you may be able to "fish" replacement insulated duct between the floors. Insulated duct is your best bet but failing that blown-in or foam would do. I'm guessing it's an older house or an added space but you should definitely fix the problem before it starts danaging the wood ceiling joists.

[energy_rater_La]

do you have access
to the space created by floor joists
from inside the main attic?

in other words...if you go into your attic
are you standing on ceiling joists/walkway/decking
for the first floor?
can you see the second floor walls??

the area created by floor joists is the area
I'm asking if you have access to.

[kls-ccc]

I think I am asking the same question Energy_rater_La is asking only in a differant way, do your second floor outside walls line up or are they inset form the main floor walls? If the 2nd floor walls are inset from the main floor then you have attic air getting into the space between ceiling and floor. I ran into one of these a couple of years ago. In the winter you could use a non-contact thermometer and tell exactly where the 2nd floor outside wall was on the Kitchen/dinette ceiling as the temp would drop about 10* there. It was actually warmer at the outside wall than it was 5' in from the outside wall when I scanned the ceiling whit the thermometer.

[genduct]

If you do have that much space please DO NOT BURY YOUR UNINSULATED DUCT IN LOOSE FILL INSULATION. If you think you have problems now. with out a vapor barrier your duct will sweat like a pig and wet insulation is NO INSULATION

[mccben10]

What type of flooring do you have on the 2nd floor? If it is carpet it's pretty easy to just roll it back and cut the plywood floor where you need too.

[allan38]

I'd have your service company cut the drywall and replace the uninsulated flex ducts. You sometimes have to make multiple holes to locate exactly where ductwork is running. I'd rather make multiple holes in drywall than subfloor. Others may do it differently.

They may know a good drywall guy, best case the entire situation could be resolved in a day or two after you call.
Insulated ducts have a vapor barrier that will stop the inner liner from sweating.
Blown in insulation won't have a vapor barrier and the duct will still sweat.
Properly installed, the standard insulated flex duct is just fine.

A dripping duct can grow mold in a building. Don't put off the repairs, it can get really expensive the longer you wait.

[tedkidd]

The ductwork may condense because your band joist is leaky. Humid air leaking in hitting cold ducts is condensing. Stop that leakage. Might also happen if you use ac intermittently without regard to dew point. When it cools down at night do you shut ac off and open windows? Do you shut ac off when you go to work?

What state are you in?

Sealing the band joist may solve it.

[rgf2912]

I'm in Charlotte NC. How would I check the band joists for leakage? I have access to an Infrared camera and acoustic monitoring equipment. I'm leaning to cut the existing drywall on the ceiling and replacing the ducts with insulated ones and then putting up new. Hate the pop corn ceilings anyway. Another idea I was kicking around is to open the envelope between the ceiling and floor to both the upstairs and downstaire using large registers. Would that work?

[rgf2912]

I did an InFrared scan of my system and it looks like 3 of the 6 flex ducts run in the space are not insulated. I'm not sure who the contractor or HVAC sub was but I'm sure that running uninsulated duct in this space is not in compliance with the code. I'm sure he saved a few bucks on cheap ductwork!!! Where can I order flex insulated duct? Any reputable places on the net?

[tedkidd]

Originally Posted by rgf2912

I'm in Charlotte NC. How would I check the band joists for leakage?

Look for discolored fiberglass. Spider webs? Most rim joists are leaky.

Blower door and smoke pencil is the best way. See how much air comes up through the basement door. Have an energy audit performed.