Product review (5 stars): New filter every year!
until recently I did not know April Air needed filter replacement. actually thought my Aprilaire didn't work.  had a separate furnace repair ( bad ignitor) and furnace repair man asked me when last time I changed filter... like never. was calcified and crumbling... I am pretty religious about changing the regular furnace air filter too .... oh well  - got two new filters and cleaned out the system and now working as intended... much better comfort in winter with some humidity in the house! now will plan on changing once a year!  On a side not I bought a small white board to put on entrance to crawl space where I can keep track of when I change my filters ...ie, when changed, when due.  keeps the guess work out of when did I change things last and don't have to get in crawl if not necessary.