Regularly changing your furnace filter is one of the best and easiest ways to maintain your home’s comfort and energy efficiency while preventing costly repairs. The longer you leave your filter in, the dirtier it gets, restricting airflow and causing your furnace to overwork.

Dirty filters can negatively impact your home’s air quality, too. Poor indoor air quality can cause headaches, dry throat, eye irritation and potentially more serious health issues. Clogged with enough dirt and other airborne particles, expired filters can also overheat to the point of becoming a fire hazard.

Keep reading for helpful hints when you’re ready to check or replace your furnace filter.

Where to find it

The filter is usually located on the furnace itself, typically in the blower compartment near the bottom. Depending on your furnace, it may also be in a door near the top or on the side. Most furnaces have built-in racks to place the filter in.

If you can’t find the filter on the furnace, it’s likely hiding behind a nearby return air grill. These can usually be easily removed with a screwdriver to access the filter.

When to replace it

Depending on the amount of dust and pet hair inside the home and the outdoor air quality, most furnace filters need to be changed every one to three months.Thicker filters (between three and six inches) can last up to six months or even longer. The recommended replacement schedule should be printed on the filter. If you’re not sure when to change yours, you can always do a visual check by taking out the filter and holding it up to a light. If the filter is too dirty to see the light through it, it’s time for a replacement.

You may need to check and change your filter more often during wildfire season, which can overwhelm your filter with airborne pollutants. Extreme temperature changes and shedding pets can also put extra strain on your filter.

Not all filters are disposable. If your furnace uses a permanent washable filter, check the manufacturer guidelines to determine how often it should be cleaned.

How to do it

Changing the filter is simple: Use your thermostat to turn off the heat, pull out the old furnace filter and slide the new one in the same way. Just make sure the arrows printed on the side of the filter are pointing in the same direction as the airflow. Since the filter cleans the air that is on its way to be heated, this means the arrows should point toward the furnace.

If you’re unsure which way the arrows should point, drag your finger across both sides of the used filter. The side with more dirt on it should be the side the air is coming from.