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I live in a 1987 colonial with siding and brick. About three weeks ago my family woke up choking at 5:00 am from a dirty/ mildew type smell. We identified it as coming from the chimney and had the chimney resealed and all all cracks cemented.

Then the smell morphed and was dry and dirty/dusty almost cigarette. When the system is off, we smell it in the return vents. When the air is off, we can smell it coming out of the supply.

It moves around the house but seems constant by the front foyer and the upstairs hallways. We have had the ductwork cleaned, the coils on the hvac cleaned and an ionizer installed in the hvac. We have had two separate companies test for mold and they have found nothing.

We have a hospital grade filtration system. We are going nuts and can't live there because my throat starts to close. We're ready to just walk away at this point but it would crush us financially. Any advice?

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  • Do you smell anything outside the house? What city is this in?
    – Jim Stewart
    May 24, 2017 at 11:16
  • Is it possible you can smell the "concrete" smell which can smell both damp and musty, from the repair?
    – BrownRedHawk
    May 24, 2017 at 11:54
  • There are now camera drones that can inspect the ducts. Does your filtration system filter smell at all?
    – ajeh
    May 24, 2017 at 16:19
  • What type of filtration system is it?
    – fixer1234
    May 24, 2017 at 18:14
  • 4
    I'm voting to close this question as off-topic because identifying/locating smells are specifically off-topic for the site per Help section.
    – fixer1234
    Jul 13, 2018 at 2:29

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When was the 'hospital grade' filtration system installed? What is the nature of the filter media and the physical arrangement of the filters? Where is the air handler located? in the attic? in a closet in the living space? in the basement?

You might try a less restrictive filter. The more restrictive the filter is, the lower is the pressure in the region between the filter and the blower motor. If there is a leak in this region, outside unfiltered air will be pulled in from a region of higher pressure, bypassing the filter and perhaps carrying musty odors. If the duct work in this region suddenly sprang a leak, then this would explain the sudden appearance of this off odor. Inspect the duct work carefully in this low pressure area.

There are reports of highly restrictive filters putting such a high load on the blower fan motor that it increased the electric current flow in the motor above the design limit and drastically shortened the service life of the motor. Could this smell be from an overheated motor?

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