Good morning all -
I am posting in the hopes of some advice on how to handle an issue that I have been dealing with with for the past 3 months.
-- Around 3 months ago, I started to notice a faint mildew / musty smell coming from the return duct on the first floor of my house. I have lived here for about a year and did not notice the smell until the start of summer. The smell became progressively stronger as the summer became more hot/humid.
-- Home was built in 2011, 2 stories with crawlspace, located in NC. Each floor is about 1500 sq feet. The crawlspace is currently vented with vapor barrier on the ground. The crawlspace is dry and I have never seen any standing water in there. The HVAC handler is located in the crawlspace. The return duct in question is roughly in the middle of the first floor layout, on the lower part of the wall, and is connected to the ducts in the crawlspace via a metal "boot".
-- My initial thinking was that the ducts themselves had mildew growth inside them, so I had the ducts professionally cleaned, which did not significantly improve the situation.
-- I had another HVAC guy come out who said that the smell was likely coming from the moisture under the crawlspace vapor barrier. The vapor barrier itself was not in good shape, old, with holes, not covering the ground fully, etc. I had him replace the vapor barrier, which now covers the ground fully and goes up halfway up the crawlspace walls and also around the foundation pillars.
-- Replacing the vapor barrier seems to have remedied the mildew/musty smell to a large extent, but I am still getting a smell from the return duct. Basically it smells like the crawlspace, which again does not smell like mildew, but smells a bit like the vapor barrier and humid air. The smell only happens when the HVAC is not running.
-- I think what is happening is that crawlspace air is seeping up through the boot in some way, and is being sucked into the house through the stack effect. In my mind the HVAC should be a "closed system", so I should only be smelling HVAC through the return, but I am somehow getting crawlspace air as well.
-- The boot itself looks to be pretty well sealed. I have added some mastic in a few places in the boot where I could feel some minor air leaks, but overall the boot seems fairly tight and well sealed on both sides, so the smell does not seem to be coming from any major leaks.
My questions:
1. Do you have any ideas on what could be the source of the smell?
2. If the issue is crawlspace air infiltrating the boot, any suggestions on how to fix? Would it be worth it to have someone come out and further seal the boot? Perhaps there are leaks in the boot that I missing.
3. Would sealing the crawlspace vents and installing a dehumidifier help? I was thinking of having this done anyway since the crawlspace gets fairly humid in the summer and the ducts tend to "sweat" when the AC is running. I am not sure if this would help if the smell is the result of the stack effect of air rising up through the house, but perhaps making the air less humid will keep it from rising through the house as quickly.
Any thoughts would be really appreciated. Thank you.
I am posting in the hopes of some advice on how to handle an issue that I have been dealing with with for the past 3 months.
-- Around 3 months ago, I started to notice a faint mildew / musty smell coming from the return duct on the first floor of my house. I have lived here for about a year and did not notice the smell until the start of summer. The smell became progressively stronger as the summer became more hot/humid.
-- Home was built in 2011, 2 stories with crawlspace, located in NC. Each floor is about 1500 sq feet. The crawlspace is currently vented with vapor barrier on the ground. The crawlspace is dry and I have never seen any standing water in there. The HVAC handler is located in the crawlspace. The return duct in question is roughly in the middle of the first floor layout, on the lower part of the wall, and is connected to the ducts in the crawlspace via a metal "boot".
-- My initial thinking was that the ducts themselves had mildew growth inside them, so I had the ducts professionally cleaned, which did not significantly improve the situation.
-- I had another HVAC guy come out who said that the smell was likely coming from the moisture under the crawlspace vapor barrier. The vapor barrier itself was not in good shape, old, with holes, not covering the ground fully, etc. I had him replace the vapor barrier, which now covers the ground fully and goes up halfway up the crawlspace walls and also around the foundation pillars.
-- Replacing the vapor barrier seems to have remedied the mildew/musty smell to a large extent, but I am still getting a smell from the return duct. Basically it smells like the crawlspace, which again does not smell like mildew, but smells a bit like the vapor barrier and humid air. The smell only happens when the HVAC is not running.
-- I think what is happening is that crawlspace air is seeping up through the boot in some way, and is being sucked into the house through the stack effect. In my mind the HVAC should be a "closed system", so I should only be smelling HVAC through the return, but I am somehow getting crawlspace air as well.
-- The boot itself looks to be pretty well sealed. I have added some mastic in a few places in the boot where I could feel some minor air leaks, but overall the boot seems fairly tight and well sealed on both sides, so the smell does not seem to be coming from any major leaks.
My questions:
1. Do you have any ideas on what could be the source of the smell?
2. If the issue is crawlspace air infiltrating the boot, any suggestions on how to fix? Would it be worth it to have someone come out and further seal the boot? Perhaps there are leaks in the boot that I missing.
3. Would sealing the crawlspace vents and installing a dehumidifier help? I was thinking of having this done anyway since the crawlspace gets fairly humid in the summer and the ducts tend to "sweat" when the AC is running. I am not sure if this would help if the smell is the result of the stack effect of air rising up through the house, but perhaps making the air less humid will keep it from rising through the house as quickly.
Any thoughts would be really appreciated. Thank you.
source https://hvac-talk.com/vbb/showthread.php?2222974-Smell-from-Return-Duct&goto=newpost
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