If the filter needs replacement proceed as follows:
- With paper or fiberglass filters you may notice that the frame is made of cardboard. Also note the arrow on the frame that shows the direction of air flow for the filter. Insert the filter back into its holding frame with air flow positioned correctly as per the arrow.
- With foam filters replace the cleaned or new filter as appropriate. These are usually frameless so you will have to position it carefully according to the design of your furnace.
- Replace the access panel or blower door as required.
- Repeat the inspection process monthly.