Have you ever entered a house and smelled the mold? Like the whole house is full of it? That was the case in this house, built in the 60s, with an entirely subterranean basement.
There was little evidence of mold anywhere, but the whole house smelled moldy.
And I couldn't find it!
The grading was good and the basement walls were dry, according to my meter, and without staining.
There was no evidence of previous flooding.
The water heater was newer, but no staining around it.
I did see a little mold under the entry staircase, which is a typical spot, but it wasn't enough to make the whole house smell like it.
Being an older house, it had the kind of HVAC system where the registers and returns are in the same room. There was no large central return anywhere.
I like those systems; they move air well and each room is comfortable.
But I do know from experience that because there are so many returns and linear feet of return that moisture can develop.
THEN I SAW THIS!
Looking further, lots of the registers looked like this!
And the ducts inside those registers, insofar as I could see!
Taking off the furnace filter and looking inside the large return beside the unit, I saw the same!
The entire duct system seemed infested with microbial growth!
Mold, fungus, whatever, it doesn't matter. It was everywhere.
Can it be remediated? Probably. But what is causing the problem?
Does this mean the insides of the heat pump is full of such growth? YES! Is the unit causing the problem? Can it be remediated inside there?
REMEMBER, MICROBIAL GROWTH IS NEVER THE PROBLEM. IT IS A SYMPTOM OF THE PROBLEM. MOISTURE IS THE PROBLEM, WHATEVER THE SOURCE. AND THERE WAS A LOT OF MOLDY HVAC STUFF IN THIS HOUSE!
Hence the pervasive smell.
I'm not an HVAC guy, but I do know that when heat pumps are installed retroactively they often do not get enough necessary return air flow to balance the output they need to blow in order to operate efficiently. Is this disparity of returned air/conditioned air volume the source of the problem?
My recommendation: if you walk into a house that smells moldy, there is a reason for that. Your nose is your cheapest, and probably best, mold detector. Everyone is allergic to some molds. What bothers you might not bother me. But mold is always a health issue, whatever the specie. And it is always a symptom of the real problem in the house - moisture.
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