DIY Network

Replace a Furnace Filter

Choosing the right filter will improve the cleanliness and efficiency of your home's heating system.

More in Electrical

  • Time

    1 hour

  • Price Range

    $1 - $50

  • Difficulty



Step 1: Check the Unit’s Filter

Indoor air can be up to 70 times more polluted than outside air. It's important to check the size and type of filter for your furnace to make sure you are using the correct one.

The filter is normally located between the return air and blower (Image 1).

Write down the correct part number of your furnace filter (this one was written on the access panel) (Image 2), so that it will be easy to find when you need to replace it.

Step 2: Remove the Old Filter

Shut off the power at the electrical switch mounted on or near the furnace.

Open the filter access panel and remove the old filter. Note the directional arrow on the filter -- all are made to filter the air in one direction. When you replace the filter, make sure the arrow is pointing the right way. Use an indelible pen to mark the direction on the furnace access panel.

There are a wide range of filters available. Disposable fiberglass filters are the most common, but filter technology has improved with the introduction of electrostatically charged filters. Although they look like ordinary filters and do not have to be wired or connected in any special way, electrostatically charged filters have been magnetized to attract and capture extremely small airborne particles of dirt and allergens in the air flowing through the filter medium.

note directional arrow on filter for future

Step 3: Size and Install the New Filter

You can purchase washable electrostatic filter medium that will last up to five years and cost approximately $30. First remove the old filter, then remove the retaining grid and old filter medium from its frame.

Measure the retaining grid, then cut the electrostatic filter medium to size.

Replace the adjustable frame around the retaining grid and new filter. Retaining pins hold the grip in place.

Wash the filter in soapy water about once a month during heating season.

It is a good idea to also have the heating ductwork cleaned by a professional service every few years. Over time, dust and pollutants can collect in the ducts and affect the quality of the indoor air, even with an electrostatic filter installed.

cut electrostatic filter medium to size