I had sewage backup that filled my basement mechanical HVAC room about 6 inches. I have two HVAC systems side by side. This means that both one-foot-long sections of the 18x30 rectangular cold air return duct under my two blowers were filled with sewage for an hour and sewage soaked the internal fiberglass insulation of that metal section of ductwork.

The sewage cleanup crew sprayed and wiped down the inside of the duct with Benefect and then used an alcohol fogger.

Now that I see that it was not a hard metal surface and is instead this fibrous insulation, I'm assuming that this has to go in the trash and the Benefect is not going to be effective?

They mentioned they'll come back to remove the insulation, but looking online it looks like there's no easy way it comes off other than scraping with a wire brush? If so, wouldn't that just get fiberglass fibers everywhere and just fill my HVAC system with those fibers?

Seems like the easiest thing for them to do is just replace the section of the ductwork completely since it's only a foot-long section on both furnaces? Should I insist on just replacing the duct rather than scraping the insulation off? Is putting Benefect on it helping at all?

Is replacing the ductwork significantly more expensive then scraping the duct?

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  • 3
    You really want to spend close personal time cleaning shitty insulation? Replace it - safer, healthier, quicker and no chance of smells at a later date.
    – Solar Mike
    Sep 6, 2021 at 4:45
  • It's hard to tell from the pics. I presume the items that got damaged are the silver boxes on which the the furnaces sit. from the pics, those look like they're sheet metal. Are you saying that there's insulation board inside those, or am I just not seeing it properly and that those are actually constructed of the insulation board themselves?
    – FreeMan
    Sep 7, 2021 at 13:33

1 Answer 1


Replacing the ductwork shouldn't be extremely expensive. Even if it was moderately expensive, I'd still do it.

Mold/sewage/ etc is nasty.

  • Would you happen to know the going rate for replacing ductwork off the ground? I see some estimation tools online but it goes by the foot - and since this is only a foot of ductwork seems underestimating - I'd imagine there are minimum base cost for just getting it started. Sep 7, 2021 at 12:56
  • If your insurance (you didn't mention anything about that) covered the clean up, there's high likelihood that it'll cover repairs, too.
    – FreeMan
    Sep 7, 2021 at 13:31
  • the sewage cleanup alone already put me over my insurance limit so everything from here on out is out of pocket :( Regardless I've been planning on just paying someone, but didn't want to get scammed as there are a lot of contractors throwing exorbitant rates since there is such a rush of people after the hurricane and short supply. I want to know what the regular price is so I can at least know how much over I'm paying and how long I can wait for the surge in pricing to go down. I'd be willing to pay more now because of demand, but not an arm and a leg Sep 7, 2021 at 13:38

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