cold air coming from return


  #1  
Old 12-16-09, 07:43 AM
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Question cold air coming from return

Hi:

I have a heating unit in my attic for the second story of the house. One area is always very cold in the winter and hot in the summer. I have found that cold air is coming from one of my return vents when the unit is not running, but not from the other. When the unit is running, there is a good flow that keeps the filter from falling out and I don't see any holes in the flex duct. Is there supposed to be some kind of flap or something that keep air from back flowing through the return when the unit is off that is working on the one return but not on the other? Is there an easy fix for this?

Cheers,
Beer 4U2
 
  #2  
Old 12-16-09, 09:49 AM
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Sounds like the two returns have decide to work together against you . Both ducts are getting cold so you have a temperature inversion with warm air on your ceiling and cold air in the ducts above. Eventually the cold air in one of them spills out which results in replacement air being pulled into the other. This creates two problems, the cold air you feel and the potential for condensation/moisture inside the ducts in that cold attic.

If you protect the ducts in the attic from the cold, wrap them and bury them in insulation, the problem should go away. Also the wrapping and burying should include all ducts up there.

Hope this helps
Bud
 
  #3  
Old 12-17-09, 10:24 AM
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ducts seem insulated

Thanks for the reply Bud. Seems that the ducts are all insulated well, though they are not buried in insulation. They are all hanging so it is not possible to bury any more. One of the returns is bigger than the other. Is this part of the problem? The cold air comes from the smaller one.

Thanks,
 
  #4  
Old 12-17-09, 11:43 AM
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The insulated ducts I have seen are about r=6, where attic insulation should be at least r=38. Since those ducts carry conditioned air they are, or are supposed to be, part of the inside of your home. I didn't say it was going to be easy , but they need more insulation, both for the problem at hand as well is simple energy costs.

We have had a few posters on the board and I have had a house recently where we dumped a gallon of water out of a duct in the attic, condensation. Nasty stuff, not something you want to live with forever.

Trying to help,
Bud
 
  #5  
Old 12-17-09, 02:59 PM
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Thanks

Thanks Bud

That is a big help. I was afraid that might be the case. Is it easy to find better wrapping for the flex duct? Guess I should go look for some

Cheers,
 
  #6  
Old 01-05-10, 08:24 PM
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Hi, I'm new to DIY and this is the exact problem I'm having. I thought the flex duct insulation was enough. I have some extra duct insulation but it is R-6. Since I have it already, can I double wrap the air return duct or do I simply need to use a higher R value insulation? The thermal inversion is something I never would have thought of and it makes sense. I thought it may be the air vent. I actually called a air/heating company today and cancelled my appt based on this thread. I may have saved myself a minimum $65 house visit.
 
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Old 01-06-10, 01:34 AM
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Upon a second read of this thread, does the inversion also apply to a single return duct? I have a single return duct. Thanks in advance for any help.
 
  #8  
Old 01-06-10, 03:02 AM
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The single return duct is actually connected to all of the supply ducts, so if it has a larger volume of cold air, then that air will fall and house air will be pulled in through the supply ducts.

All ducts in unconditioned spaces need to be sealed and very well insulated. A six inch duct is 1.5 sq. ft. per linear foot. twenty fee of that is 30 sq.ft. of exposed surface and when the air is moving, it is just like a wing chill factor in terms of heat loss. You should be alright doubling up the insulation you have, just make certain there are no hidden air leaks. Foil tape (can be removed if needed) or duct mastic (there to stay, no changes) for sealing.

Bud
 
  #9  
Old 01-19-10, 10:22 AM
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I have the same problem. Is there any louvers/baffles/anything that one can install on the return air duct vent/opening that would close when the furnace/AC is off and open (by air movement) when it is running?

Seems like a simple solution to me, but I can't find anything on the market that meets the requirement.
 
 

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