My CARRIER furnace model no is: FK4CNF002. The existing filter has these two numbers on it: KFAFK0212MED and 31-659-402. I'm not sure if this is an original filter or an improvised one. As I bought the house in 2005 and since then the filter hasn't been changed.
I live in Gaithersburg, Maryland. Where can I buy the filter for my furnace. I cdn't find this filter or a similar sized one at Home Depot, or the local hardware stores. Thanks - Musawir

Try this place, and just enter the filter's PN:
AmericanHVACparts.com (http://www.americanhvacparts.com/)

Try this place and just enter the filter's PN:
AmericanHVACparts.com (http://www.americanhvacparts.com/)