Where is my Furnace/AC filter located?

Up flow Furnace (air moving upward) Filter is located in the blower compartment bottom door adjacent to the cold air return. You have to remove both the top door and then the bottom door. Make sure that when you re-install the bottom door, it goes over the furnace frame so that it engages the safety switch. If not the furnace will not run.

Down flow Furnace. air moving in downward direction Filter is located in the upper blower compartment. Most furnaces will have a V shape filter system, the system will take 2 filters. The filters go up into the plenum in a V shape. Make sure that when you re-install the top door, it goes over the furnace frame so it close the safety switch. If not the furnace will not come on.

Horizontal Furnace. Most Horizontal Furnaces will have a slide in Furnace rack, built directly into the furnace.

Air Handlers. Most Air Handlers will have a built in filter rack in the unit. Note most Air Handles will have central returns, which have built in filter grills to accommodate your filter.. Check to see that you do not have a filter in the Air Handle and the filter grill. This will cause you reduced air flow and higher bills.