I did the same thing when I was out of AP flour during a snowstorm last winter. My snickerdoodles turned into these thick, puffy rounds that stayed soft for days. Nobody complained, they just asked why I hadn't done it sooner. Now I keep a bag of bread flour around just for cookies.

Call your HVAC guy and ask if he's trying to sell you a more expensive filter.

Oh totally, I get that. Reminds me of a buddy who drove the same forklift for so long he claimed the steering wheel had fingerprints worn into it (which honestly, I sort of believed). Makes you wonder if the seat eventually just becomes part of your body, like a weird permanent attachment.

I got the same deal as you, @valthomas, and it's been totally worth the three bucks a month for me.

Jumped into DIY insulation myself once and it really shows how we all think we can shortcut stuff until we hit that wall. Same thing happened with my cousin redoing her bathroom grout, she used the cheap premix instead of mixing her own, now it cracks every winter. It's like that urge to save a few bucks on a project blinds you to the fact that some things are just built for pros. The smell you mentioned is the kicker, that means it's off gassing wrong and could be a health thing. Better to call a spray foam crew, they got the rigs and the masks, and they can do a small attic in a morning without turning your house into a science experiment gone bad.