# Basement air coming up through vents and returns



## glsmith (Jun 1, 2012)

I have a five year old house, so relatively new construction. Three levels, dual HVAC "zones", with the main furnace in the basement which feeds the basement (90% finished) and the main floor. A smaller furnace in the attic feeds the upstairs. There are also two air conditioning units for the same zones.

The basement furnace is in the 10% unfinished part, which is also used for storage. The furnace is a 90% efficiency model, and I have two fresh air ducts from the outside that vent close to the furnace. I don't have any temperature problems in the basement, nor moisture that I can tell (I live in a very dry climate).

My question mainly has to do with the "storage room smell" (dusty, musty, kind of hard to explain but noticeably not fresh) that seems to come from the storage room up through my ducts. The smell is most notable when the heat is on -- I can smell it coming out of the vents on the middle floor -- but is also noticeable when the air conditioning is on or the furnace vent. Also, when the HVAC system is completely off, on certain days I can smell this musty air coming out of my returns on the main floor, as well as the registers. As if the air is flowing up from the storage room and coming through whatever openings are available. I would guess this means the pressure on the main floor is lower than that downstairs, so air flows up.

It seems to me I might have a variety of problems, such as leaky ducts. I've plugged as many gaps as I can find, but I still smell the storage room in the main house, again even when the HVAC system is off. Is there a way to prevent air from seeping up from the storage room? Any way to prevent my forced air system from pulling in the storage room air and circulating it throughout my house?

Thanks for any ideas.


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## Marty S. (Oct 31, 2009)

I'd suggest a two pronged approach. First seal all the joints on any exposed duct in the basement and all the duct in the attic. Secondly seal all penetrations that go into the attic including around the register boots. 

From the post it sounds like some stack effect going on. Warm air is rising and going out all the holes in the attic (wire holes,plumbing stacks,ducting ect). It's being replace with outside air via the fresh air ducts that dump into the furnace room. It's then seeping into the duct and going throughout the house. A bucket of mastic,some tubes of caulk and a few fun filled hours in the 120 degree attic and you'll have it whipped.


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## Johnny'sHotDogs (Jun 1, 2012)

I agree with Marty S. It should increase efficiency and may solve the problem. Two other things to consider: 1. when was the last time the unit was cleaned and serviced? There could be mold on the evaporator and/or the condensate line could be blocked, allowing water to remain in the unit that could produce a “swampy” smell. 2. In newer construction, and depending on your local codes, and the builder, your supply and/or return ductwork may be flex. If this has any dips anywhere it could collect water and produce the same “swampy” smell.


One possible way to check would be to place a strong, but pleasant, smelling candle or even an open bowl of pine-sol in the furnace room. Turn the system off. If you start to smell it upstairs, your issue is probably external to the system. If you still smell the musty smell it is probably internal. Do this after sealing everything as suggested.


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## vln (Jun 19, 2011)

It could be DDS or, "Dirty Sock Syndrome". You can only smell it when the air conditioning or fan is on, but not with the heat. This problem also effects gas furnaces, but it most common with heat pumps. I would get your installer out ASAP before any warranty you have may run out. The only foreseeable cure is to install a "coated coil".

http://www.foxservice.com/austin/knowledge_base.asp?ID=1291219433792&_perPg=40&view=articles&_category=Residential%3A%3AAir%20Conditioning%20%26%20Heating%20&_filterField=Categories

http://www.achrnews.com/articles/a-cure-for-the-dreaded-dirty-sock-syndrome

http://www.centralcityair.com/information/library/dirtysocksolution.pdf


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## glsmith (Jun 1, 2012)

Johnny'sHotDogs said:


> I agree with Marty S. It should increase efficiency and may solve the problem. Two other things to consider: 1. when was the last time the unit was cleaned and serviced? There could be mold on the evaporator and/or the condensate line could be blocked, allowing water to remain in the unit that could produce a “swampy” smell. 2. In newer construction, and depending on your local codes, and the builder, your supply and/or return ductwork may be flex. If this has any dips anywhere it could collect water and produce the same “swampy” smell.
> 
> 
> One possible way to check would be to place a strong, but pleasant, smelling candle or even an open bowl of pine-sol in the furnace room. Turn the system off. If you start to smell it upstairs, your issue is probably external to the system. If you still smell the musty smell it is probably internal. Do this after sealing everything as suggested.


Thanks for the reply. Some additional information now that we're going down this path... I have done the test you suggest, using an incense stick. I essentially just walked around the storage room with the smoking incense, and had my wife verify that the smell quickly spread to the middle floor of the house. So I'm fairly certain that my ducts are leaky, and I've already gone the mastic route and sealed whatever gaps I could find. That didn't help that much, and didn't stop the air from seeping up when the system was off.

To be clear (wrt some of the other replies), when I say "upstairs" I mean the middle floor of my house, which uses the same duct work as the basement and the main furnace. I have no noticeable problems with the upper floor/attic which has its own furnace and duct work.

Yes, the basement furnace has been recently cleaned, as well as the ducts (not sure if that was a good thing or not). It sounds like the problem is external to the system based on some of the replies here and my tests, probably really leaky ducts. The weird thing is that I get such a pronounced smell even when the system is off.

I plan to have pretty much the entire duct system that is still accessible in the storage room replaced (an HVAC guy I've been working with has pointed out some incorrect installation, more gaps, etc), which should take care of some of this problem.

What does this group think of solutions like AeroSeal? 

Other thoughts I've had is to have the 10% unfinished basement area finished to hopefully seal in the air in that room, preventing it from seeping upwards when the system is off. At this point, money is no object I just want the smell to go away...


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## Johnny'sHotDogs (Jun 1, 2012)

I have never dealt with AeroSeal. I just watched their promo video. It looks like it could work. I would contact the local contractor and ask for references from customers serviced more than a year ago. They are the ones that will be able to address cost savings and air quality issues.


Since you have an HVAC guy taking a look, get another one or two, and compare prices and recommendations. Go with what makes sense. Even if money is no object, there is no need to waste it.


Before finishing the last 10% I would suggest having a moisture test and checking for foundation leaks. Better safe than sorry.


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## glsmith (Jun 1, 2012)

Johnny'sHotDogs said:


> I have never dealt with AeroSeal. I just watched their promo video. It looks like it could work. I would contact the local contractor and ask for references from customers serviced more than a year ago. They are the ones that will be able to address cost savings and air quality issues.
> 
> 
> Since you have an HVAC guy taking a look, get another one or two, and compare prices and recommendations. Go with what makes sense. Even if money is no object, there is no need to waste it.
> ...


Thanks for the great advice...


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## BenC. (Sep 5, 2016)

Hi, did you ever find a solution to this problem? I am dealing with the exact same thing in my new house. First floor furnace is in the basement and is pulling up the air from the basement. The second floor is fine because the furnace is in the attic.


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## stephjg (Jul 12, 2018)

Did anyone ever solve this issue? I have the exact same problem and am going insane!




BenC. said:


> Hi, did you ever find a solution to this problem? I am dealing with the exact same thing in my new house. First floor furnace is in the basement and is pulling up the air from the basement. The second floor is fine because the furnace is in the attic.


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## stephjg (Jul 12, 2018)

Hi! Did you ever find a solution?


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## Archmonty (8 mo ago)

stephjg said:


> Did anyone ever solve this issue? I have the exact same problem and am going insane!


did anyone ever figure this out? We have the same issue ands been 3 yrs and driving us crazy!


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## Nealtw (Jun 22, 2017)

Archmonty said:


> did anyone ever figure this out? We have the same issue ands been 3 yrs and driving us crazy!


So you have a fairly tight house, but people and pets use air, fans in bathrooms, over the range and dryer pump air outside, and the only way the house can replace the air is thru the fresh air vent to supply air for the furnace. 
So the fresh is coming thru the smelly room and surprise it spreads the smell thru out the house.


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## rogerwh (Mar 1, 2021)

Archmonty said:


> did anyone ever figure this out? We have the same issue ands been 3 yrs and driving us crazy!


Check out the return air ducts, in the basement, that are hanging below the floor joists. Look on the top of these ducts. Some time they cut holes in the top of the duct and hang then from enclosed floor joist for return air. They don't get the hanging duct, tight up to the floor joist and they leak air.
If you have enclosed floor joist for return air, check where they intersect with the main return air duct.


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