Replies

1. 
   homedesign | Jun 07, 2011 05:08pm | #1

   Mark,
   Perhaps an air leakage problem or lack of insulation as you say...also
   I wonder if you have closed some registers in other rooms....?
   I have seen this cause the air speed to increase at certain registers and the metal becomes extra-cold.
   another possibility....
   Your AC may be oversized and short cycling and not removing enough moisture.

   Avoid opening the doors.

   A last resort (temporary)would be a standalone dehumidifer about $250-$300 at the big box store

2. 
   BobHr | Jun 07, 2011 05:40pm | #2

   Are you talking about registers in the basement? I would guess that you have an air leak from outside bringing in warm moist air. The area above the cieling should not have much air movement, from inside the house, to be carrying the humidity above the ceiling...indoor air would be dryer than outside air. That would lead me to believe that it is air leaking from outside.

   Again I am assuming this is in the basement. The sill plate and rim joist area is where to start the investigation. From the exterior you can investigate the bottom of the siding. See if the are any gaps that would allow air up behind the siding.

   Another thing is the cores of concrete blocks. I have seen sill plates that are not the same width as the block. This leaves part of the core (holes) open at the top. Since the area affected is behind a finished ceiling you will have to check for this in an unfinished area. Reach up and see if the sill plate reaches to the edge of the block or if you can feel the openings for the cores. Also check to see if there is a gasket under the sill plate.

3. 
   4WNfu4aYeK | Jun 07, 2011 08:09pm | #3

   This is a 2 story house all above ground in Garland Tx. The house has only one 4 ton system for the whole house. I had an HVAC guy today tell me that perhaps the house needed a draw vent on the opposite side of the house downstairs to help remove humidity from the house. I have one draw at the top of the stairs and one near the den where the garage entrance downstairs. Since the house was purchased as a rental foreclosure theres no telling if they remodeled and eliminated a draw from that side of the house in the downstairs. We actually found one at the den
   while remodeling.

   Hmmm short-cycling. Interesting have heard about that one but I like the possible idea of adding a dehumidifier. Not sure though. I would like to sell the house someday perhaps owner finance but need to get this resolved.

4. 
   user-659915 | Jun 07, 2011 11:30pm | #4

   Draw vent? Is this another name for a return air register?

5. GBA Editor
   Martin Holladay | Jun 08, 2011 03:48am | #5

   Mark,
   Possibilities include:
   1. The occupant is operating the AC in an unusual way -- for example, living without AC for a day or two (allowing the indoor RH to rise) and then turning on the AC so that the register gets cold before the house air is cool and dry.

   2. The forced air system is unbalanced because some ductwork is located outside the home's thermal envelope. If some supply ducts are in the attic, and the duct seams are leaky, then the entire house can become depressurized. This depressurization can draw in outdoor air at the rim joist area, bringing humid outdoor air into the joist bays, leading to condensation.

6. 
   4WNfu4aYeK | Jun 08, 2011 09:40am | #6

   Yes the draw vents also called return air registers. The attic had about 18" of insulation blown in last year. Based upon the family that lived there, someone was usually in the house all the time.
   I did notice that they were trying to run the system at 69' thats not really possible and puts unusual strain on the system. It had been raining heavily a few weeks back and it did get really humid for awhile. I am pricing whole house de-humidifiers as a permanent solution. They ain't cheap.

   I will check the garage as a possible unbalance area. Because we had a squirrel and a raccoon issue last year and they managed to eat or gnaw thru some of the truss material in between the floors. This could definately let in humidity from the outside and have caused the depressurize situation.

7. 
   homedesign | Jun 08, 2011 11:03am | #7

   Mark,
   I think you should have an Energy Audit done
   Whole House Dehumidifier is not the solution.

8. 
   BobHr | Jun 08, 2011 11:35am | #8

   Is this slab on grade or is it on over a crawl space.

   Before you spend any money on band aids get to the source of the moisture.

   If I am understanding correctly the metal duct above the ceiling is sweating and running down on to the ceiling. The area above the ceiling is a semi closed space, that is it is not air tight from inside the house but does not have large volumes of air flowing through it. The air inside should be dryer than exterior air too. So I do not think indoor RH is the cause.

   I still feel that there is an air leak(s) from the exterior that is letting in large amounts of warm moist air. This moist air hits the cold pipe and condenses. The souce of moisture is from the exterior and from many different points.

   I doont know why this site does not promote energy audits.When we have an injury we expect the doctor to take xrays or have an MRI to see inside our body. An audit does the same thing.

   An energy audit can be a very valuable diagnostic inspection of the house as a system. Martin made some good points about unbalanced systems, ducts in the aittic etc. Get an energy audit using a blower door and a thermal camera. The blower door quantifies the leaks, the camera helps locate leaks and finds hidden conditions like an xray would. If you have duct work in an attic or crawl space then have the duct work leak tested with a duct blaster.

   I think a dehumdifier is not the solution. The dehumidifier setup works when you have a energy efficiect house and the ac does not have to run enough to dehumidify. What you have is a 20-30 yo home that was not built air tight nor well insulated. You goal should be improving the air and thermal barriers.

   As a side note insulating the attic will do nothing to stop air leaks. Dont get a false sense of security that the insulation is doing much good. The insualtion could be blocking attic/roof vents and causing harm so I would investigate the install.

   Some other things not brought up are does the top floor have any soffits or can lights. Is the attic properly vented.

9. 
   4WNfu4aYeK | Jun 08, 2011 01:10pm | #9

   The sweating is from what I can tell only on the metal registers. If you pull them off and put your hand up on the inside of the duct you will not feel any water or condensation on it. Although we have sprayed alot of a spray on rubber compound, as part of a solution. This is a slab house. I will check on an energy audit company and costs.

10. 
    homedesign | Jun 08, 2011 01:34pm | #10

    Mark,
    Are the problem registers fairly close to the air handler?
    Cold high velocity air could be making these registers much colder than other registers in the home.
    I had a similar problem in my last home.(in Dallas)