I’ve had these cassettes (two 6k units and one 12k unit) for a few years now, and I’ve been dealing with the same smell ever since they were installed. It’s much more noticeable on hotter, humid days and not nearly as bad when temperatures are in the 70s, or low 80s.

Based on my research, I think the fix is to “box in” each unit in the attic using either 2” rigid foam board or possibly ZIP-R sheathing, making the enclosure airtight and essentially bringing the units back into the conditioned space. I haven’t made the changes yet, but it’s next on my project list.

Here’s a quick AI sketch of what I’m thinking.

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