What Is a Furnace Filter?

A furnace is an expensive and vital home appliance, and you want to make sure it gets all the proper maintenance and repairs. Properly filtering the intake on the HVAC system is a key component to its effective operation that will last for years. Here, you can read all about the basics of furnace filters, starting with an essential question, what is a furnace filter?

What Does a Furnace Filter Do?

A furnace filter is an invention that improves air quality in a home or building by preventing contaminants from passing through the furnace. Depending on the rating of the filter, it can trap pollen, dust mites, dander, etc., and prevent them from circulating back into the air you breathe through the home’s vents.

Where Is My Furnace Filter Located?

You will find it somewhere between the return air grille and the furnace, usually inside the blower compartment. For somebody in a warm climate with a downflow system, you likely have a filter grille where the furnace in the attic and the filter are housed within the return air grille in the ceiling (so you don’t have to climb into the attic to change it). If you have an upflow system, you either have a furnace in the basement or the main floor, and the filter is housed alongside or beneath the furnace or behind a wall grille.

Learn more about upflow vs. downflow furnaces

What Happens If the Furnace Filter Is Backwards?

Though not a perilous mistake, a backward filter is definitely an error you want to avoid. The contours of the filter are designed for the most efficient airflow. A backward installation will resist airflow resulting in an increase to your utility bill, and it may damage the furnace by putting extra stress on it.

What Does a Dirty Furnace Filter Look Like?

If you’ve ever cleaned the lint from the dryer, it’s going to have a similar appearance, with more texture to it. The pleats of your filter are probably white (although you’ll see green and other colors), so if you see gray everywhere, it’s definitely dirty.

How to Install a Furnace Filter

Installing a furnace filter is just a matter of access. It’s so easy if you know where your filter is located. If it’s within the return air grille, then you need a screwdriver to open it up. Remove the old filter and replace it. Then close up the grille with the screwdriver. If the filter is located adjacent to the filter itself, you can probably slide the filter out without opening a panel or needing a screwdriver.

We have a longer article with specific instructions for changing a furnace filter here.

Save on Filters and More

Now that you know all the basics, it's time to buy a new filter for your home. Don't forget, we carry a huge inventory of HVAC parts like motors and blowers, furnace ignitors, switches, etc. Did you know that you can find member pricing here on certain items (typically name brand, MAP priced items) if you log in? For industry professionals buying in bulk, please consider contacting us directly for extra special pricing and extra savings.