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insulating furnace return air duct (wierd case)


Browndav's Avatar
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09-23-06, 05:34 PM   #1  
insulating furnace return air duct (wierd case)

Greetings all,

I think I may have finally found one of the main causes of my high heating costs during winter.

Basically, the problem is the return air duct to my NG furnace goes through the attic, out the eave, through a couple 90* bends, then down into the furnce into the room below. As labeled in the picture below, there is only ~1" of roll type insulation and a layer of sheet metal between the duct and the outside world.

There's a picture here: http://www.ma-uav.com/images/air_duct.JPG

Due to this, during the winter when it doesn't go much over freezing for weeks at a time, all the warm air from in the house has to pass through this area, and probably gets significantly cooled right before it gets to the furnace, requiring much more gas to heat. Also, when the furnace isn't running, this is a much more direct path for heat loss than through the 2' of blown insulation in the attic added last winter.

So, I'll list a couple options I've come up with, and would like comments or additional suggestions.

1 - Pull sheet metal off and replace insulation with 1.5" thick pink foam, R7 (or R7.5).
pro - cheap, quick & easy, doesn't require any new construction
con - not very much insulation really

2 - Use some of this stuff: http://www.insulation4less.com/highr_FfmF.asp
pro - much thinner than the pink stuff, twice the R-value, no new construction, can find similar stuff cheaper at home depot.

3 - Build new enclosure around it to add ~8" of normal batt roll insulation.
pro - can get high(er) R value
con - needs to be built to accomodate the extra insulation

4 - Do nothing. Not really an option. The wife and I are tired of paying $60+ a month for gas to keep the house at 55*F

Overall, I'd prefer to take the time to do it right, add as much insulation as possible.

Thanks for any comments or suggestions,
-Dave

 
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Ed Imeduc's Avatar
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09-23-06, 05:47 PM   #2  
looked at the picture not sure just what you have there. But as i cant get in and see it all Id say go with your #3

ED

 
Browndav's Avatar
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09-25-06, 10:14 AM   #3  
Posted By: Ed Imeduc looked at the picture not sure just what you have there. But as i cant get in and see it all Id say go with your #3

ED
sorry about the poor picture. Here's a couple more much higher quality ones. (if you have winXP, you can make them bigger by hovering over the lower right corner and clicking the icon that shows up)

http://www.ma-uav.com/images/DSCF0081.JPG
http://www.ma-uav.com/images/DSCF0082.JPG

There's only 6 inches between the sheet metal and the furnace exhaust pipe. There's only 4.5 inches between the sheet metal and the metal flange around the base of the exhaust pipe (shown best in the second picture above).

So, there's not much room for more insulation
Also, currently the sheet metal exterior is flush with the edge of the eaves. So going any thicker would make it extend past the edge of the eave (not really a problem if done right)

Thanks for the reply,
-Dave

 
Browndav's Avatar
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10-01-06, 08:29 PM   #4  
I'm still looking for more opinions about this, especially since I don't think I have room for ~8" of insulation like I initially thought I would.

Thanks,
-Dave

 
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