# Ductwork Deodorizer



## Chris Sweeney (Apr 20, 2012)

I'm looking for something to deodorize the ductwork in my house. The ducts are clean, but I still have a smell that comes through at certain random times (when the unit is off). No, I'm not talking about the urine-like dirty coil smell, because, well, I don't have a coil; it's just a gas fired furnace. Rather, it smells like the inside of the walls (the same "inside-the-wall" smell I smelled when gutting my bathroom). I can smell it coming from the return vents at random times when the unit is off. In the exposed basement ceiling, I can see that the main return is running between 2 ceiling joists covered by a 16" wide piece of sheet metal and not through actual ductwork, and it may be the same situation in the walls (not running through ductwork, but through the walls themselves), which may be where my smell is coming from. Not only do I want it to kill the odor, I want it to kill whatever bacteria/etc. is causing the odor (which I understand may not even be the case). Suggestions?


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## Philly Master (Mar 30, 2013)

Chris Sweeney said:


> I'm looking for something to deodorize the ductwork in my house. *The ducts are clean*, but I still have a smell that comes through at certain random times (when the unit is off). No, I'm not talking about the urine-like dirty coil smell, because, well, I don't have a coil; it's just a gas fired furnace. Rather, it smells like the inside of the walls (the same "inside-the-wall" smell I smelled when gutting my bathroom). I can smell it coming from the return vents at random times when the unit is off. In the exposed basement ceiling, I can see that the main return is running between 2 ceiling joists covered by a 16" wide piece of sheet metal and not through actual ductwork, and it may be the same situation in the walls (not running through ductwork, but through the walls themselves), which may be where my smell is coming from. Not only do I want it to kill the odor, I want it to kill whatever bacteria/etc. is causing the odor (which I understand may not even be the case). Suggestions?


 How was this determended ?

returns too ?


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## Chris Sweeney (Apr 20, 2012)

Philly Master said:


> How was this determended ?
> 
> returns too ?


Because I had them (supplies and returns) cleaned by a reputable duct cleaning company


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## digitalplumber (Jul 8, 2011)

If I were you, i would address the real issue which is your open return, based on your description. I would not look to mask the odor.


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## SPS-1 (Oct 21, 2008)

I tend to agree that you need to get to the root cause rather than masking it. I am not an HVAC expert, but I believe running the returns through joists is done commonly (done on my house anyways) without problems with odors. 
But if you really want to spray something in there, you can go to an auto parts store and by HVAC deodorizer. Its a spray can that is sometimes sprayed into the cars ducts to kill bacteria that forms from the condensation on the car's AC evaporator. I would guess that its mostly alcohol, and comes in various scents. Its going to get a little expensive if you are trying to spray your whole duct system. Lysol would be a lot cheaper, but I am not sure if it would be as effective.


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## Chris Sweeney (Apr 20, 2012)

digitalplumber said:


> If I were you, i would address the real issue which is your open return, based on your description. I would not look to mask the odor.


Open return? What do you mean? The return ducts in the living areas of the house are running down the walls and into the main return line in the basement (which runs between the joists and is covered by sheet metal, which apparently was a standard practice according to other HVAC guys) and then into the return boot and then the furnace. I'd say it's operating in a "closed circuit", but I could be wrong. What do you mean by "open return"?

Also, I'm not looking to mask the odor either. As I mentioned before, I'd like to get rid of whatever is causing the odor (i.e. bacteria or whatever) if possible.


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## digitalplumber (Jul 8, 2011)

open studs, no lined ductwork or fiber board.


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## Chris Sweeney (Apr 20, 2012)

digitalplumber said:


> open studs, no lined ductwork or fiber board.


Gotcha, thanks for the clarification.


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## wkearney99 (Apr 8, 2009)

Chris Sweeney said:


> Because I had them (supplies and returns) cleaned by a reputable duct cleaning company


Yes, and of course they actually did what you paid to have done... Because you where there and saw the horrendous amount of filth that came out of your ducts. Right?


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## gregzoll (Dec 25, 2006)

My guess is that you have a critter doing this. Going by some duct cleaning company, they are probably trying to sell you something else.


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## Chris Sweeney (Apr 20, 2012)

wkearney99 said:


> Yes, and of course they actually did what you paid to have done... Because you where there and saw the horrendous amount of filth that came out of your ducts. Right?


Darn right I was. They're actually a good friend of the family with 4 generations of being in business, and they let me do the work with them.  Don't worry WK, I wasn't one of those people scammed with a bait-and-switch duct cleaning service like in that 20/20 special from a few years ago.



gregzoll said:


> My guess is that you have a critter doing this. Going by some duct cleaning company, they are probably trying to sell you something else.


Just out of curiosity, how would a critter be doing this?


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## gregzoll (Dec 25, 2006)

Raccoon's, mice, Tree rats that get inside will do it. Even a dead one can cause a stink for a long time. Our Trailblazer makes the same type of smell on a hot day, when the windows are closed up, and you crank up the a/c on recirc.

It is actually a bacteria that if you do not run the heat or run the blowers without the a/c on, will smell like animal pee, or a old dirty sock. The only other thing to do, is while running, spray in a light mist of bleach water, of 1 part bleach, 50 parts water, to help kill anything in the chamber in the car.

As for hvac equipment, do you have a humidifier on this unit? When was the last time bleach water was poured in the tray for the A-Coil, and drain lines cleaned out with Bleach water?

Also is this unit in the basement or Attic, or any duct work that passes through the attic? If you are smelling it specifically in the bath, my guess is that someone missed the pot and hit the duct, or a friend or previous owner may have done it in the past, and the duct cleaning caused the smell to reactivate.


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## Chris Sweeney (Apr 20, 2012)

gregzoll said:


> Raccoon's, mice, Tree rats that get inside will do it. Even a dead one can cause a stink for a long time. Our Trailblazer makes the same type of smell on a hot day, when the windows are closed up, and you crank up the a/c on recirc.
> 
> It is actually a bacteria that if you do not run the heat or run the blowers without the a/c on, will smell like animal pee, or a old dirty sock. The only other thing to do, is while running, spray in a light mist of bleach water, of 1 part bleach, 50 parts water, to help kill anything in the chamber in the car.
> 
> ...


Sorry Greg, perhaps you missed a few posts at the top. I specifically mentioned that there is no urine smell (no dirty sock smell) because there is no coil to be cleaned; I don't have A/C, just a forced hot-air gas-fired furnace. What it smells like, rather, is the inside of the walls; a concrete/cement smell, the smell I experienced when doing the demo work ripping out the walls (which weren't drywall, but not plaster either; some sort of cement/concrete or something) in my bathroom. My assumption, then, is that this smell is due to the returns possibly running open through the wall cavities between the studs.


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## COLDIRON (Mar 15, 2009)

Take a couple pieces of the metal down and shine a light in there check for dead critters.. Calgon makes a little pad you can put in with your filters to deodorize the house. You can also put any type deodorizer in the return air flow. One more thing make sure the panning is tight and not drawing air in from a stinky source.


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## gregzoll (Dec 25, 2006)

Chris, just making sure we are covering all bases. Now if construction or destruction has been done in the place, air being pulled through the returns can pull those debris through, along with associated smells in the house.

Another item you could get is an ionizer and run that to see if it will remove any smells in the house. The big problem with duct cleaning, is that if you are still doing work in the place, you just threw out everything you just spent, due to dust and fine particulate is still being pulled through the system.

Yes, the Gypsum & plaster smell will linger for a few days. This is a big reason why people shut their systems down while doing this kind of work, due to it will gather on the fan cage in the furnace so thick, that it can actually wear out the motor quicker.


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## wkearney99 (Apr 8, 2009)

The walls, did they have wood strips running across? Not that it'd matter with regard to this issue, but that's old plaster and lathe style wall. They lay on a first coat of fairly coarse plaster that looks quite a lot like concrete, just not as heavy. Then they lay on subsequent layers with finer grades until a skim coat for finish. Between that and modern drywall there were one or two other methods, usually involving some form of drywall-like sheet and added layers of finishing plaster.


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## Chris Sweeney (Apr 20, 2012)

wkearney99 said:


> The walls, did they have wood strips running across? Not that it'd matter with regard to this issue, but that's old plaster and lathe style wall. They lay on a first coat of fairly coarse plaster that looks quite a lot like concrete, just not as heavy. Then they lay on subsequent layers with finer grades until a skim coat for finish. Between that and modern drywall there were one or two other methods, usually involving some form of drywall-like sheet and added layers of finishing plaster.


No plaster & lath, but the walls were exactly what you mentioned at the end. It's not plaster/lath, nor is it regular drywall. It's some sort of wallboard with something cementitious on top of that. The first layer of the cementitious topcoat has some bigger aggregate in it, like tiny stones. Then the final topcoat was a smooth cementitious mix of some sort with no aggregate. It was hard to cut and actually ruined my keyhole saw.

Thanks again for all the responses so far. I really appreciate you all taking the time to help me!


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## wkearney99 (Apr 8, 2009)

Yup, we had something like that in the old house (circa 1950). I think I know the smell you're talking about. Dusty, dry, rock-like sort of smell. It's likely dust left over from demolition of the old walls. We had a bit of that with the old place. We did the ducts when we moved in, but demo'd the bathroom several years later. The key to eliminating it was replacing the filters frequently. It worked out for us to replace the filter every 3 weeks, using the basic model. Then once the filter wasn't showing obvious signs of dust I upgraded to more expensive ones. I also obtained a short duct brush, the kind used for cleaning dryer vents, and used it on any ducts near the work. Just enough scrubbing to help dislodge anything that might've been an issue.


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## FClef (May 5, 2013)

Locating the origin of odors can be very tough. Can you smell this odor in your basement? I am more inclined to believe that you may be drawing the odor from there than from your walls, unless of course you have a rampant mold problem somewhere as yet unidentified within the ceiling or walls. A simple and easy test to see if it is being drawn in through your basement is to turn your fan on and then take a stick of burning incense and move it around your return area, not only will you see the smoke from the incense being drawn into any leaks you will also get the smell upstairs. Of course the standard caution is be careful with the lit incense that you don't draw embers into the ductwork etc. etc.


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## Chris Sweeney (Apr 20, 2012)

wkearney99 said:


> Yup, we had something like that in the old house (circa 1950). I think I know the smell you're talking about. Dusty, dry, rock-like sort of smell. It's likely dust left over from demolition of the old walls. We had a bit of that with the old place. We did the ducts when we moved in, but demo'd the bathroom several years later. The key to eliminating it was replacing the filters frequently. It worked out for us to replace the filter every 3 weeks, using the basic model. Then once the filter wasn't showing obvious signs of dust I upgraded to more expensive ones. I also obtained a short duct brush, the kind used for cleaning dryer vents, and used it on any ducts near the work. Just enough scrubbing to help dislodge anything that might've been an issue.


Exactly the smell you described. For some reason I couldn't find the words to describe it, but you hit the nail on the head with you description. Good tips, thanks!


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## biggles (Jan 1, 2008)

might want to cycle the heat and burn off that heat x and heat the supply duct up...then cool it al down and see if it disappears.if you have heat only these are non fan running smells if you don't have a summer fan option wired into the furnace?


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## Chris Sweeney (Apr 20, 2012)

biggles said:


> might want to cycle the heat and burn off that heat x and heat the supply duct up...then cool it al down and see if it disappears.if you have heat only these are non fan running smells if you don't have a summer fan option wired into the furnace?


The smell appears sporadically/randomly. I first noticed it in early spring 2012, which is the first spring I lived here. I've run the furnace in winter 2011-2012 when I first moved in, and then in winter 2012-2013. No summer fan option  In other words, when I move the thermostat to Cool or Fan, the blower doesn't turn on; only when I have the thermostat switched to Heat.


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## wkearney99 (Apr 8, 2009)

Have you had the furnace professionally serviced? Might there be something accumulated on the heat exchanger? 

And do you have a carbon monoxide detector (at least one) installed and operating? If there's any issues with the furnace causing off smells then I'd be doubly vigilant about CO poisoning risks.


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## Chris Sweeney (Apr 20, 2012)

Yes, there is a working CO detector right next to the furnace unit, and it has been serviced this past spring. The ducts were already really clean, so now they should be even cleaner. The furnace works nicely, and the filter is barely even dirty when I go to switch it out.


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## biggles (Jan 1, 2008)

no humidifiers mentioned.something is being triggered by temp changes...in the filter in the return duct and sealed as so it isn't sucking in basemen air


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## CandCsmom (Jan 17, 2014)

*Dirty smell in ducts still after cleaning*



Chris Sweeney said:


> I'm looking for something to deodorize the ductwork in my house. The ducts are clean, but I still have a smell that comes through at certain random times (when the unit is off). No, I'm not talking about the urine-like dirty coil smell, because, well, I don't have a coil; it's just a gas fired furnace. Rather, it smells like the inside of the walls (the same "inside-the-wall" smell I smelled when gutting my bathroom). I can smell it coming from the return vents at random times when the unit is off. In the exposed basement ceiling, I can see that the main return is running between 2 ceiling joists covered by a 16" wide piece of sheet metal and not through actual ductwork, and it may be the same situation in the walls (not running through ductwork, but through the walls themselves), which may be where my smell is coming from. Not only do I want it to kill the odor, I want it to kill whatever bacteria/etc. is causing the odor (which I understand may not even be the case). Suggestions?


Chris Sweeny - did you ever resolve this problem? I have the exact same odor and system setup and I am at our wits ends! Its gotten to the point where I won't turn the heat on and would rather be cold than smell that noxious dusty smell blowing into the room (the only time I smell the odor is coming from the supply registers when the fan kicks on or when I set it to run fulltime). I have an original to the house (built in late '40s) gas fired furnace, no AC or coils. The duct cleaning company has been out 3 times (also very reputable been doing business with them for years/family friends). On the third time out he discovered one of the return runs was situated over another run and was missed when initially cleaned (reconstruction in the basement which I'll get to in a moment - I can see why he missed it the first time). When he opened that one up to clean it it released a huge dust cloud and I was hoping that was the mysterious source. After thoroughly cleaning everything again - and thoroughly cleaning the ungodly amounts of dust released into the house AGAIN, I was hoping that the problem had been resolved. Not. The odor has definitely lessoned in strength but it is definitely still there and as I said it is definitely coming from the supply registers when the heat (or just fan) is turned on. The duct guy also went through and tore off all old duct tape and resealed everything visible including sealing up some of the opening at the filter on the unit where he thought maybe it was drawing in basement dust and air. My concern is - because it smells EXACTLY as you describe- like dirty construction dusty, clay, cementy dirty smell in the walls (NOT urine, NOT dirty sock) - my concern is there are leaks in the duct lines inside the walls which are not visible. I was hoping someone here would have a solution or a method of isolating the source of the leak and/or odor. I also want to know if it is bad health-wise to be smelling this odor. Is it a bacteria causing the odor?? (the system has been sprayed a couple of times now with a natural biocide). I have two young kids with allergies and one with asthma, and so far neither seem to be affected by the smell - or the dust, but it just can't be good. It also seems me and my husband are the only ones who are ultra-bothered by it. The smell is so awful it makes my whole house unpleasant. When other people come over they notice it right away but not like we do (maybe bc we are soooo exasperated over it!) It is noticeable when you first walk into the home but after a few minutes you get used to it and don't smell it anymore until the furnace kicks in and then if you are standing near a register the smell just hits you full face. FYI the house has recently undergone a major renovation - the basement and kitchen were totally ripped out and rebuilt (before we moved in). It is my understanding that the system may or may not have been shut off during the construction and that dust and debris could have gotten in which is why the previous owner had it cleaned and then we had it cleaned again before moving in but this "construction" odor is still there. It had also undergone a major mold remediation (the reason for ripping out the entire basement down to concrete and studs) and mold is definitely gone/not a problem anywhere in the house. I am very sensitive and allergic to mold and that is definitely not the smell and I am having no reactions I would normally have to mold even when standing in front of the registers and breathing in the smell . All mold issues were resolved - just want to be clear so no one thinks that is the source. Anyway, after the third time out the duct guy said the system was clean and the "problem" was due to residual construction dust in the basement and living space of the house that was getting sucked in and still circulating. I don't totally disagree but that can't be the full explanation. This house has been cleaned top to bottom so thoroughly several times now. And the system is still generating a lot of dust (filter is dirty within days of putting in a new one) and there is a fine dust covering everything even hours after I just dusted. I have looked at the blower and fan blades and into the ducts as far as we can see and have replaced all the register covers and all of that is clean. I still feel like there must be breaks in the system somewhere to be expelling that amount of dust still into the living space along with the odor or perhaps there is another run that was "hidden" like the one he just found due to the reconfiguration of walls and ceiling in the basement when it was remodeled. Other than starting over with a new company and more money (and like I said I really trust and know the duct guy we used anyway) I don't know what else to do except keep the system off. And its too cold here in Northern VA to be doing that in January! Any help is greatly appreciated!


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## wkearney99 (Apr 8, 2009)

Um, use some paragraph formatting?

As for dust, it's better to be replacing cheap filters more often than trying to eek out longer use of more expensive ones... So buy 'em in bulk and change them out more often.

One suggestion might be to have a plumber come out with a video inspection camera and fish that down the ducts. Get a look-see in there to determine if there's anything still in the ducts.


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## CandCsmom (Jan 17, 2014)

Thank you. I did think of that - someone coming out with a camera to scope it out, but wasn't sure who to call or how much it would cost. 

I've been replacing the filters about every 5 days - that's how quickly they've been getting dirty (black with accumulated dust balls). I think we've changed 9 or 10 so far in the last 2 months since moving in. Yes switched to the cheap ones after shelling out for the $$$ ones the first few times. 
Sorry about the paragraph formatting. I accidentally hit "post" b4 having a chance to go back and edit. Not intentional.


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## wkearney99 (Apr 8, 2009)

If you're having to change filters that often then there's something seriously wrong. 

No way a system that'd been properly 'cleaned' would leave behind enough material to have the filters getting dirty again that quickly. Not unless there's some horrendous amount of debris in a duct somewhere (that they didn't clean out). 

Black? Not just dark gray like typical dust? Do you have a working carbon monoxide detector in the house? Because black dust on the filter would make me start thinking about the furnace leaking combustion materials and the soot getting caught by the filter. But if actual soot is getting into the ducts then so would carbon monoxide, which IS DEADLY. Be SURE about this. 

Anything's possible, of course, but at this point getting a look-see inside those ducts would seem like the best plan.


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