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Any solution for toxic smell coming from HVAC duct work

user-3828327 | Posted in Energy Efficiency and Durability on

Harrisburg, PA

7 July 2023

Hello Green Building Advisor and People of Wisdom and Experience,

We’re into the second summer in our new home. We generally do not use AC and didn’t make use of it during our first summer. However with parents coming to stay for the week we cranked up the AC in their upstairs bedroom today (happened to be during the hottest part of the day) prior to their arrival.

Holy cow, the upstairs began to smell like a toxic waste site, I can still taste it!

So, after I shut the AC off I went looking and found that the duct work in the attic is made of a flexible material, the outside is a black plastic.

Called the company that installed the geothermal system & duct work and was told that the plastic smell just had to “burn off” since we hadn’t been using the AC until this season (we did use the system to heat the home and hadn’t encountered this).

The duct work and HVAC unit reside in the attic, there is mineral wool insulation on the floor of the attic, none on the ceiling and the attic is vented.

After having poked around in the attic I can understand perfectly where the toxic smell is coming from, it seemed like it was 1000 degrees up there and super heated everything and when I turned on the AC it filled the air and bathed everything in I don’t know what but it wasn’t good.

I figure that we’re gonna have to put mineral wool on the ceiling but I’m sure that the space will still heat up. We have solar panels on the front of the roof 
and I thought that that might have blocked some of the radiant impact but no, it was beastly hot in that  attic.

Can duct work be changed out to a metal material?

Any other suggestions????
Many thanks,

Judy – Harrisburg, PA

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  1. walta100 | | #1

    There is an HVAC symptom called “Dirty Sock Syndrome” you may want to read about it and see if it could be related to your symptoms.,odor%20is%20bacteria%20and%20mold.

    Yes, steel ductwork can be install almost anywhere It costs more and requires skills that are becoming less common as demand shrinks.

    Adding insulation to the roof line alone is a risky game in that the dew point of the air in the attic could sometimes get above the temp of the wall and water could condense things could get moldy and rotten.

    You could condition the air in the attic that would require the removal of the old insulation from the floor installing expensive spray foam insulation at the roof line and adding supply and returns registers in the attic space to keep it more or less the same as the rest of the home.


    1. user-3828327 | | #2

      Hello Walta,
      thanks for the input. took a look at the article you referenced, my husband lives in a cloud of that "dirty sock" smell so I'm familiar (he's charmer so the scales are tipped in his favor) and what I was smelling was a very strong plastic/chemical odor.
      had no idea of the problems adding insulation to the ceiling might cause, thank you for mentioning that
      looking into metal ductwork might be an option, we know a union sheet metal worker so
      we'll be asking lots of questions
      many thanks

  2. Expert Member
    DCcontrarian | | #3

    I would get a definitive diagnosis before redoing the ductwork.

    You may find it easier just to add more insulation right over the ductwork.

    1. user-3828327 | | #5

      Thanks for the input DC_Contrarian, it'd make sense to get to the root of the problem, right.
      I just never thought about going to an HVAC company other than the one that did the install.
      thanks for the push

  3. walta100 | | #4

    I agree with DC until you identify the exact source of the smell don’t spend money replacing stuff that may not be the source.

    Note was a trap install in the condensate drain line? If not the blower fan could pull air thru condensate drain line from the sewer.


  4. user-3828327 | | #6

    Hey there Walta,
    I will go ahead and follow up on your suggestion about checking for that trap
    thanks very much

  5. Expert Member
    Akos | | #7

    I think your HVAC person is right, you need to "burn off" the VOC. The part of VOC we find annoying is the volatile part but this is also your friend as things tend to evaporate over time. VOCs from most plastic and sealant off gas over time as long as you provide some airflow, this means running the system with the windows open. In most cases this should bring the smell down. You can get a VOC sensor to monitor things but even your nose will do a decent job.

    This is the one problem with any system that has plastics and adhesives, some are better but almost all will have some smell when new. Even with hard pipe, if this system has never run, I would expect some smell when new.

    Even something meant for fresh air can off gas, for example my ERV core had a distinct smell when new, I let it run at in bypass at full tilt for a couple of days and the smell was gone.

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