We have a fairly new heat pump with gas furnace backup for cold days. When it was installed they added a second return and made sure to make me aware to only use fiberglass filters because the pleated ones restrict air flow too much.

My mom's house has a slightly older heat pump with electric "heat strips" as backup. Dad passed away in May and the air filters were one of those things he always did. She used the few that were left, and has the system serviced in October. The tech installed a wooley looking filter that looks like a hybrid between the two. From what I recall dad used pleated filters. I have no idea if that is what they should have been using or if I should switch back to fiberglass. Any recommendations one way or the other, or as far as what I should look for to determine which is appropriate?

Thanks,
Charles