I'm wondering if anyone has any guesses on this -- for the past few weeks, I've noticed a strange smell occasionally. It smelled a lot like cat pee, and I've been going nuts trying to figure out where my cat could have gone pee (going around each room sniffing the baseboards, using a blacklight, etc). It was appearing in every room of the house, and I was starting to get really angry at my cat for apparently secretly peeing everywhere. No evidence of it, and with wood floors in all of the house, I would have found it eventually!

I finally noticed today that the smell is appearing quite strongly when my heat turns on. No, my cat is NOT peeing into the heating ducts -- they're up near the ceiling, not in the floor.

Any guesses what it might be? I have a Lennox Merit Series heater, gas. If I open the little closet that the heater is in, nothing smells funky in there. But, in the 2.5 years that we've lived here, we haven't had the ducts cleaned, and I suspect the person living here before us hadn't done it in ages. Could that be it?

I'm going to call the HVAC guy regardless, but I was curious to see what people might think it is. I've now apologized to my cat for blaming him :)