Changing the furnace filter is an easy task that is often overlooked. Change your furnace filters every three months to prolong the life of your furnace and provide peak airflow (and heated air) to your house.
Most furnaces have an easily accessible access panel on the front of the plenum (air chamber). Slide open the panel and you should see the filters sitting inside the furnace. Carefully remove the filters and note the orientation of the airflow. It is important to place the new filters with the arrow pointing in the direction of the airflow for proper operation.
The filter on the left has been in the furnace for about three months. Lots of dirt, dust and debris on the filter medium. It has been doing it's job, but is starting to get clogged. You can see a clean and dirty filter side by side in the middle picture. The filter on the right is brand new and ready to be put in the furnace.
Buy the correct filter or filters and put them back in place. There will be an arrow on the filter indicating the direction the air needs to flow through the filter for it to work. Orient the filter in the correct direction and then close the access panel.
Make it easy for yourself the next time - put some reminders on the front of the furnace or plenum. I use a piece of blue tape to note the date that I changed the filter. Every time I change them, a new piece of tape goes up with the most current info. I also wrote the specs for the filters right on the front of the plenum, much easier to have that to reference when I'm ordering new filters.
Brian Jovag, owner of Jovag Home Inspection.