How to replace a furnace air filter

replace a furnace air filter

Whether or not you suffer from allergies or asthma, replacing or cleaning your furnace air filter should become part of your regular home maintenance routine.

When your furnace is on, clean air flows up through the furnace through your air ducts and into your living spaces. Without a clean air filter, the dust that is disturbed from the forced air goes into your living spaces. With a clean air filter, the dirt gets trapped in the filter instead of spreading into your living spaces.

You’ll reap important benefits from replacing or cleaning your air filter regularly. These include saving energy (reducing global warming), reduced utility bills, improved air quality, extended furnace life, and less dust in your home (that means less cleaning for you).

Replacing or cleaning your air furnace filter is an easy task. Most manufacturers recommend replacing or cleaning your filter monthly. However, if you’re unsure, check your furnace’s operations manual. Most filters are located in the return air duct near the blower fan. If you can’t find the filter, check the manual.


  1. Turn off the furnace. Before replacing or cleaning the filter, turn off the furnace’s electrical switch. If you have a gas-fired furnace, turn off the gas valve. The switch is usually located alongside the furnace cabinet near the gas valve and controls.
  2. Open the blower doors. Blower doors usually lift up and then out or swing open. On some models, the door is located on the top of the blower.
  3. Remove the filter. Slide the filter out of its channel. As you do, notice the placement of the filter so that when you replace the filter, it placed in the proper position.
  4. Hold the filter up to the light. If you can still see light through the filter, the filter is still usable. Just slide it back into its channel and you’re done. If you can’t see light through the filter, then it’s time for a change.
  5. After removing the filter, look for dirt on or around the blower. Miscellaneous dirt can clog the furnace and cause it to malfunction. Vacuum or sweep up the dirt before replacing the filter.
  6. If you have a permanent filter (usually dry foam), vacuum or wash the filter with cool water. If you wash the filter, be sure to let flow through the channels until all the dirt is removed. It might help if you use a hose to pressure wash some of the tighter spots. Tap the filter lightly on the side of the washtub to get most of the water out. Then, you’ll need to let the filter dry out for at least an hour before you put it back into the furnace.
  7. If you do not have a permanent air filter, you probably have a fiberglass filter. Look at your filter and note the model number and size. If you do not have a replacement, throw the old filter out and purchase a new one from a hardware or home improvement store.
  8. Replace the new filter the same way in which you removed the old one. A fiberglass filter will have one side that is oily. This is the side that faces the blower. Most filters have an arrow that indicates the direction of the airflow and makes it easy to determine which way to install the filter. The arrow needs to point towards the blower.
  9. After the filter is in place, close the blower door and make sure it is firmly latched. Then, turn the furnace’s gas valve or electrical switch back on.

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