Hello all,

I performed an audit the other day and one of the homeowners' largest concerns was a funky smell in the ducts that serve the upper stories (of a 3-story row home in Washington, DC). The smell is similar to that you will find in a bouse house (i.e. porta-John).

The smell came while running the heat. 

The HVAC unit for the upper stories is an air-source heat pump.

The heat pump and ducts were recently installed by the guy who was flipping the house. An HVAC permit was not pulled.

Any ideas on what may be happening? 

Thanks,

Patrick

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have you tried to run a blower door there?  it really has little to do with what I think is happening, but if this is the problem, it will amplify it quickly so you will know. 

did the remodelor somehow cut the plumbing vent line?  did he leave it dead ended in the attic or somewhere in a wall?  do you have a malfunctioning vent termination?  I don't know what they call them, but occasionally plumbers put a termination on a vent line that is supposed to only let air in, but never let air out of the plumbing vent.  they are commonly burried inside a wall. 

running heat may change pressures enough to make something that works at 0 stink at +/-1. 

I have accidentally found broken plumbing vents in 2 houses, and several where the vent terminated inside the attic while doing a blower door test. 

not the most pleasent experience. 

It's possible that a leaky return duct could be sucking in gasses from a terminated vent line.  BTW they're called, air admittance valves (generically) among other things and yes, they can malfunction.  If your code permits them, they are restricted to one per living unit, should be installed horizontally, and must be readily accessible (not buried in a wall) if installed correctly, among other things.  I would be more inclined to insure that all ducts are sealed and then trace the path of the vent pipe from the point that it penetrates the roof down through each of the plumbing fixture groups before beginning the search for a malfunctioning AAV.  A borescope might be helpful.

Thanks Dick, that is helpful.

Reading your reply reminded me that I forgot to mention an important fact...the ducts are all flex duct, but there may have been some pan-joisting for the returns.

I will still try to trace the vent pipe and see what this may tell me.

Patrick

I hope not.  Pan-joisted return ducts are the leakiest of the leakiest ducts.  A very bad idea.  I think the first priority here is to find the source of the obnoxious and dangerous fumes and the second is to figure out how to seal the return.  Hopefully the return is not too long and you can convince the owner to replace it with a conventional duct with all seams sealed with mastic.  Short of that, you could try house wrap tape, but to me, that's a distant second choice.

I hear you Dick.

I was not happy to see the pan-joisted return ducts, and I made this known to the homeowner. I think this homeowner is a smart cat, and will do what is required to resolve this situation, especially if I tell him that we may be facing a dangerous issue.

As for the sealing of the pan-joisted return ducts, I am a firm believer in the power of duct mastic. Ideally one would replace such ducts (as you mention), but I take what I can get.

Thanks Dick!

Patrick, two thoughts:

1. I mistakenly said that AAV's should be installed horizontally.  It's just the opposite, should be vertically.

2.  If the owner elects to try to seal the existing pan-joists, perhaps a one-part foam would be the best answer as I'm sure that neither mastic nor tape are tested or approved for metal to wood or drywall contact.

Good luck!  Would be interested to see you come back and tell us the outcome of the story.

Thank your sir.

I'll make sure to follow up.

Open sewer vent during blower door test...been there, done that...yuk! In my case, plumbing fixtures were not yet installed so I taped over the openings so I could keep down my lunch.

Agree that wall cavity joists are an energy disaster, also a fire hazard. If nothing else, perform a ductblaster test to highlight the leakage almost certainly occurring.

I had funky smell in my ductwork too,

my HVAC tech fixed my ductwork but the smell didnt go away, i bought 2 unit of dual lamp uv germicidal and the moldy smell start go away! its really work.

i reseach prices arroud for the dual unit, and i find the best one on ebay, here is the link

http://www.ebay.com/itm/Air-Purifier-UV-LIGHT-ultraviolet-AC-hvac-d...

Obviously all of the prior recommendations could be correct however there is another possibility. In the HVAC industry it's typically referred to as "Dirty Sock Syndrome". It occurs in heat pumps and shows up in the heating cycle. The smell is the result of microbial growth on the indoor coil. Typical treatment options involve cleaning the coil. Some of the most effective methods are a three step process that involves cleaning the coil, then treating it with an anti-microbial agent and a coil coating that inhibits growth on the coil. In many cases this must be repeated every year or two. A quality UV light properly installed and maintained can kill the organisms and prevent them from returning. Of course this is more effective if the coil is cleaned and treated first.

There are several chemical companies that have effective products for this issue; NuCalgon and Atlanta Chemical are two of them.

Thanks a lot Kevin.

I will soon take all of these recommendations to the HOs, and then work with my HVAC partners to hopefully resolve this issue.

I'll follow-up if and when we resolve this issue.

Hi Patrick, just curious if you ever determined what was causing the smell and what the solution was to correct the issue

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