Shop by
Most HVAC issues trace back to a neglected filter. An old, dirty gray filter is a clear sign for a replacement. As dust builds, airflow drops and your HVAC system has to work harder, driving up energy use. Swapping in a fresh filter and switching to high-efficiency air conditioners can lower cooling energy use by as much as 20%–50%.
Look at the edge of your old filter. You’ll see numbers like 20×20×1—that’s the “name” size. The real size is usually a half-inch smaller, so a 20× 20×1 filter is really about 19½×19½ inches. Write those numbers down; they’re the ones you’ll use when you buy a new filter.
No old filter to check? Measure the opening in your furnace with a tape measure. Round each number up to the next inch; that’s the size you need. Turn the furnace off, slide a filter in to be sure it fits flat with no gaps, and order a custom size if the slot is odd-shaped.
First, cut the power so you stay safe. Flip the switch beside the furnace, slide the thermostat to “Off,” or trip the breaker in the panel. With the power off, the fan can’t start while you swap the filter.
Find the filter slot—it may sit behind a return-air grille in a wall or ceiling or inside the HVAC unit itself. Open the cover and gently slide the old filter straight out so dust doesn't spill. Take a moment to wipe any loose dust inside the slot; this helps the new filter fit snugly and keeps debris from blowing into the system. Remember the direction of the airflow arrow on the old filter so you can install the new one the same way.
The old filter will contain dust and other debris, so it helps to have a trash bag handy and to disturb the old filter as little as possible.
Insert the new air filter into the empty space, ensuring that any directional arrows on the filter point toward the unit. If there are no arrows present, the direction does not matter.
Finally, pop or screw the cover back in place for improved air quality, system protection, and reduced electric bills.
Once you’ve figured out how to replace your furnace filter, you should make it a regular exercise. It is all too easy to forget about replacing furnace air filters, so it is a good idea to make a note on your calendar or add an alarm to your phone as a reminder to check the filter’s condition. Buying replacements in bulk or setting up a recurring shipment can also help you keep consistent with your replacements and reduce the likelihood of procrastination. When you set up a recurring shipment with Filterbuy, we reward you with a 5% discount and a guarantee that your filters will always be delivered precisely when you need them.
Keeping a clean filter can shave up to 15 percent off your electric bill because your system doesn’t have to work as hard. A new filter costs just a few dollars, so changing it on time is an easy way to save money and breathe cleaner air.
Order replacements directly from Filterbuy. Our filters are made in the USA, ship free, and are backed by 7,000 + customer reviews. Choose your size and delivery schedule on the product page, and we’ll handle the rest.
A new, clean filter (white) next to an old, dirty filter (gray). Changing the air filter keeps the air in your home clean by trapping dust and allergens. It also helps your furnace or AC work correctly, so it doesn't have to work too hard and risk damage. A fresh filter allows air to flow freely, saving energy and helping your system last longer.
ENERGY STAR recommends inspecting your filter every month. If it already looks dusty or gray, replace it right away; otherwise, install a new one at least every three months. Homes with pets, smokers, or allergy concerns may need more frequent changes, so let the filter’s appearance guide you.
Take a look at your filter. A clean one is usually white or light-colored, but a dirty filter looks gray or brown and is covered in dust and hair. You can also hold it up to a light, and if hardly any light shines through, the filter is clogged and should be replaced.
If you don't change the filter, it gets clogged with dust and cantle air through. This causes your furnace or AC to work significantly harder, and it may overheat or shut down. You might get weak airflow, poor heating or cooling, and higher energy bills. In the worst case, a clogged filter can even cause your system to malfunction.
Most filters have the size printed on the side of the filter (three numbers for length, width, and thickness). You can also measure the old filter or the slot with a ruler if you're not sure. Once you know the size, you can buy a replacement at a hardware store or online. For example, Filterbuy offers a handy tool where you enter your filter size, and it displays the correct one.
Replacing the filter is easy and can be done by you. For safety, turn off your furnace or AC first. Then, slide out the old filter and slide the new one in, ensuring the arrow on the new filter points toward the furnace (in the direction of airflow). Turn the system back on, and you're done.
Use a filter that fits your system and suits your needs. For most homes, a standard pleated filter is effective in catching dust and pet hair. If someone in your home has allergies, choose a higher-quality filter that traps very tiny particles. You usually don't need the most expensive filter unless you have special air quality concerns.
Most furnace filters are designed to be replaced, not cleaned. Trying to wash or vacuum a dirty disposable filter won't remove all the dust, and it can even damage the filter. It's best to put in a brand-new filter, so you know it's clean and works properly.
It's not a good idea to run your furnace or AC without a filter. Without a filter, dust and dirt can get inside the system and cause problems. If you have to run it briefly because you don't have a replacement, it might be okay for a few hours, but try to get a new filter as soon as possible.
In most systems, the air filter is right next to your furnace or indoor AC unit, often in a slot on the side or bottom of the unit. It might be behind a small cover or panel that you can slide off. Look for a thin slot or opening near where your system draws in the air — that's where the filter sits.
