AC Plenum and/or air duct leaks

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  #1  
Old 10-06-18, 01:55 PM
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AC Plenum and/or air duct leaks

My attic air leaks into the rooms, I checked the plenum (in attic) and duct work many times, but could not find any leaks. All I did was try to feel by hand when AC is on and also visual check all joints, hopefully I can see some problems, but may be the leak is too small, so far I did not find anything. Another point, even the AC is not on, I can still smell a little attic air in my room. I even turned AC off for 3 full days (no fan either), the attic air still get into my rooms, I can smell the attic air near the register area. My question is: is there a better way to find the plenum and/or duct work leaks? Thank.
 
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Old 10-06-18, 02:11 PM
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I knew this problem is AC related. No such problem before a new coil was put in 3 weeks ago, They replaced the coil and also a section of the plenum (some plenum area was rusted out ) and also replaced a couple of air ducts 3 weeks ago.
 
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Old 10-08-18, 04:14 AM
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Have you taken the registers off and sealed between the boot and the sheet rock?
 
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Old 10-08-18, 04:24 AM
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I agree that you may need to better seal ductwork intrusions into your living space.
It is possible that the work on your unit improved return air to the point it is causing air to be drawn into your living space.

Also, do you have proper venting of your attic.
This could cause air to stagnate in the attic causing the odors to be noticeable.
Improving venting could be the answer to your problem.
 
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Old 10-09-18, 08:08 AM
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What I don't understand is the new section of the plenum and the new air duct are all at the cold air side (not return air side), so if those area leaks, it should only blow cold air out, not draw attic air in. The new air ducts did not reach the registers, only a section was replaced. so no change in the register area. Air flow may be increased a little, but as I said, even without AC or fan, the attic air still get into rooms..
 
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Old 10-09-18, 08:19 AM
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I just found a hole at the furnace vent pipe right outside of the plenum. Can attic air sacked in from here ?
 
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Old 10-09-18, 08:26 AM
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The solution is likely simple.
You have either missed seeing a defect in the return air ducting and attic air is being drawn into airhandler or a lack of attic venting is causing the odor to be forced into your living space.

I strongly suspect a lack of attic venting because an attic should not have any odor.
It's likely a problem that has existed for a long time but only obvious because of a small change.

Describe in detail the attic and how it is ventilated.
Some clear pics of the attic and roof would also help.
 
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Old 10-09-18, 08:33 AM
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What is a "vent pipe"?
If it is on the supply duct it could be pressurizing the attic or if a return duct drawing attic air into air handler.


It still is likely you have bad attic venting and the odor in your house is a symptom of another problem.
 
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Old 10-09-18, 09:33 AM
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I understand the attic venting issue, but nothing else changed except a coil, a section of plenum and 2 sections of air duct. Now even with AC off, no fan, the attic air gets down to the rooms. very small amount, I can smell it some time, not all the time. I do have a whole house exhaust fan, may be that fan sucks the air from the registers if there is a leak somewhere around plenum or air ducts, but stop using this fan does not seems help much, hard to tell. Are there any tools to check the air leaks ? or color air ? smoke ? so I can see, etc....
 
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Old 10-09-18, 09:38 AM
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Vent pipe--- Gas furnace exhaust pipe, just wonder in AC mode, if air can be sucked in from a hole of this pipe ? I don't think so, just to make sure.
 
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