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Old 07-28-2006, 07:20 AM   #1
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Attic Smell from A/C - I'm at wit's end!


I am getting that musty, dusty attic or insulation smell from by A/C vents, and it is more pronounced when very hot outside.

To paint a proper picture . . . the house is only 2 years old and has dual-zone cooling. The upstairs furnace is in a small part of the attic where the insulation is rolled. The rest of the attic has blown insulation. Because the "blown" side represents the largest part of the attic, most of the return and supply ducts run to it from the "rolled" side.

Last year, to help with costs and efficiency, we had additional insulation blown in to the "blown" side. Since then, the A/C has smelled like the attic, though we notice nothing from the heat in the winter.

I recently when up there and taped up all the joints, nipples, and boots so minimize cold air blowing into the attic (or being sucked from the attic). The contractor had failed to do this. I checked the ducts, and none have fallen loose or broken (all have R6 insulation around them). I had the original A/C contractor back, and he claims no insulation is collecting on the coil (I don't know how to check this myself).

We have ridge and soffit vents, though I noticed that insulation has made its way into (and blocked) several of the soffit vents.

I am not saying the A/C ducts are now air tight, but I certainly did as good a job as most contractors would do. I don't think I can put any more foil tape on the ducts! Any ideas? Could the lack of ventilation in the attic be the culprit? Is there something else to check on the furnace?

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Old 07-28-2006, 08:10 PM   #2
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Attic Smell from A/C - I'm at wit's end!


I guess I do not understand...musty and dusty...Is it wet up there? Have you checked the condensate line from the AC/? Is it broken, does it have a pump on it? Is it working? You should be able to find the condensate drain line and water should be dripping from it while the AC is running. check this out and post back.

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Old 08-01-2006, 03:30 PM   #3
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Attic Smell from A/C - I'm at wit's end!


is the smell coming from all the vents the same or from 1 more than the other??? If it is from all the vents the same then you might want to check the ducting going to the return. If the smell is stronger from 1 vent then check the ducting going to that vent. When you had insulation blow in they may have accidentally broke/put a hole in a duct (but you checked that). Good luck. You may need to have a HVAC tech come out a pressure test the ducts and seal them from inside if needed.

Last edited by brownerd; 08-01-2006 at 03:32 PM.
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Old 08-01-2006, 03:37 PM   #4
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Attic Smell from A/C - I'm at wit's end!


How do you seal the ducts from the inside?

The only logical conclusion to this is, despite my efforts at foil taping every duct, boot, and joint, the hot attic air is still getting in.

So, how do you seal from the inside, as the lost post stated?
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Old 08-01-2006, 10:46 PM   #5
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Attic Smell from A/C - I'm at wit's end!


Quote:
Originally Posted by cidsamuth
How do you seal the ducts from the inside?

The only logical conclusion to this is, despite my efforts at foil taping every duct, boot, and joint, the hot attic air is still getting in.

So, how do you seal from the inside, as the lost post stated?
Well, from what I can tell it's a little luck and a lot of magic!
Apparently they use some sort of aerosol that sinds the leaks and fills them with a glue of sorts. From what I hear it is an involved process that requires the duct to be sealed off while they are spraying the sealant (you don't want it coming out the vent). Here in California it is required that duct sealing be done on all new HVAC installations.
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Old 08-02-2006, 01:41 PM   #6
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Attic Smell from A/C - I'm at wit's end!


Cid,
In the summer, I notice the "hot attic" smell when I come in @ 5PM and the set-back thermostat turns on the A/C.
I have sealed and fixed all of the original mess left by the "experts".
It may just be the hot smell you notice.
Pete
By the way, the Great Stuff foam works great for sealing duct work to plenums if you have the flexible duct.
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Old 08-03-2006, 06:13 AM   #7
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Attic Smell from A/C - I'm at wit's end!


add a attic fan to circulate the air in the attic on high temps,does the drain to the evaporater have a trap installed and where does it drain to?the filter location pulling in attic air?all duct work, plenums well insulated
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Old 08-03-2006, 03:20 PM   #8
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Attic Smell from A/C - I'm at wit's end!


Quote:
Originally Posted by Pete Gotchall
Cid,
In the summer, I notice the "hot attic" smell when I come in @ 5PM and the set-back thermostat turns on the A/C.
I have sealed and fixed all of the original mess left by the "experts".
It may just be the hot smell you notice.
Pete
By the way, the Great Stuff foam works great for sealing duct work to plenums if you have the flexible duct.
Yea, the "experts" really do lousy jobs.

I found insulation on the coil (after an expert said the coil was clean). As stated, I had to seal all joints after an expert installed the system.

The smell is still there, even though the coil is clean. I am having the ducts professionally cleaned Tuesday, so maybe that will fix things.
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Old 08-04-2006, 11:41 PM   #9
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Attic Smell from A/C - I'm at wit's end!


best way is to have a insulating contractor come in and spray the ducts in the attic with close cell poly foam insulation. It has to be closed cell not open cell. That will seal them tight and make unit more efficent also. This is always done in new construction when homeowner chooses to go with poly spray foam insulation. The only difference is the use a open cell for walls and ceilings and close cell for ducts. Or is it the other way around. I think i have it correct.
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Old 08-07-2006, 04:13 PM   #10
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Attic Smell from A/C - I'm at wit's end!


Quote:
Originally Posted by 747
best way is to have a insulating contractor come in and spray the ducts in the attic with close cell poly foam insulation. It has to be closed cell not open cell. That will seal them tight and make unit more efficent also. This is always done in new construction when homeowner chooses to go with poly spray foam insulation. The only difference is the use a open cell for walls and ceilings and close cell for ducts. Or is it the other way around. I think i have it correct.
Can this be sprayed inside of the ducts? Who does this? Do you know of any national contractors?
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Old 08-09-2006, 11:52 AM   #11
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Attic Smell from A/C - I'm at wit's end!


Quote:
Originally Posted by Pete Gotchall
Cid,
In the summer, I notice the "hot attic" smell when I come in @ 5PM and the set-back thermostat turns on the A/C.
I have sealed and fixed all of the original mess left by the "experts".
It may just be the hot smell you notice.
Pete
By the way, the Great Stuff foam works great for sealing duct work to plenums if you have the flexible duct.
Do you have a whole house fan? I have noticed that smell in my house too. My HVAC return is near the louvers for the whole house fan - I suspect air is being drawn from the attic via the fan louvers. Something to think about if you have a fan.
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Old 05-30-2007, 03:53 PM   #12
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Attic Smell from A/C - I'm at wit's end!


Quote:
Originally Posted by cidsamuth View Post
I am getting that musty, dusty attic or insulation smell from by A/C vents, and it is more pronounced when very hot outside.

To paint a proper picture . . . the house is only 2 years old and has dual-zone cooling. The upstairs furnace is in a small part of the attic where the insulation is rolled. The rest of the attic has blown insulation. Because the "blown" side represents the largest part of the attic, most of the return and supply ducts run to it from the "rolled" side.

Last year, to help with costs and efficiency, we had additional insulation blown in to the "blown" side. Since then, the A/C has smelled like the attic, though we notice nothing from the heat in the winter.

I recently when up there and taped up all the joints, nipples, and boots so minimize cold air blowing into the attic (or being sucked from the attic). The contractor had failed to do this. I checked the ducts, and none have fallen loose or broken (all have R6 insulation around them). I had the original A/C contractor back, and he claims no insulation is collecting on the coil (I don't know how to check this myself).

We have ridge and soffit vents, though I noticed that insulation has made its way into (and blocked) several of the soffit vents.

I am not saying the A/C ducts are now air tight, but I certainly did as good a job as most contractors would do. I don't think I can put any more foil tape on the ducts! Any ideas? Could the lack of ventilation in the attic be the culprit? Is there something else to check on the furnace?
I know that it has been a year since your air conditioning problem but I wondered what the resolution was? We are having the same attic smell from our upstairs AC that you reported and the professionals say that there is nothing wrong yet the smell is intense as the outside temperature increases. Thanks for your time.
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Old 05-30-2007, 06:21 PM   #13
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Attic Smell from A/C - I'm at wit's end!


What type ducting do you have? If it's fiberboard duct, a musty smell will develope if the fiberglass gets wet for a period of time. I've seen this when the board was installed after getting wet during the rain and being hauled to the job site in a truck. The glues in the duct don't set well with watersoaking.
You could also, perhaps have a spit off from the indoor coil, depositing moisture on the fiberboard. This will cause a smell especially after sitting for a while and molds will also develope on the surface.
Cut into the supply (and some cases the return) duct at the air handler or furnace to inspect the duct.
Duct that has gotten wet enough to produce the smell, then dried quickly will show no signs of getting wet, but will stink anyway.
Let the unit sit in the off position for 30 minutes, then just as you turn the fan on, smell the air from one of the outlets the farthest away from the indoor unit. If you smell the stink imediately- it is the ducting, if the smell takes seconds to reach your nose, the stink is coming from the indoor unit or right near it or the return.
If you have metal ducting, the insulation in the air handler or furnace may have gotten wet and smelly and need replacing.
The drain should be trapped and draining properly and not allowed to dry if it is going into any house plumbing.
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Old 06-01-2007, 10:45 AM   #14
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Attic Smell from A/C - I'm at wit's end!


clear the soffits add insulation baffles then you can push the insul. back into place
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Old 07-03-2008, 07:19 AM   #15
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Attic Smell from A/C - I'm at wit's end!


You are getting suction out of your attic from one of two places or both. They are the attic access door if it is inside your home or from can lighting fixtures, when your a/c kicks on the return air vent is sucking this heated air in thru these areas .

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