Here's How Often You Should Really Change Your Furnace Filter

A furnace filter should be changed about once every three months. A furnace filter should be changed more often in the event of pollen, construction dust, cold spells, or other amplifying factors. During furnace downtimes, the filter can be changed less often.

Flat panel filters made of fiberglass or synthetic mesh are less efficient than pleated filters and should be changed every 30 days.

Tip

Pleated filters have more surface area than flat panel filters, so they filter out more particulates.

Why You Should Change Your Furnace Filter

A clean furnace filter lets air flow freely and helps the furnace work better. Air from inside the house is sent back to the system to be heated via a return duct. The filter intercepts this air and filters out particulates before the air reaches the air handler. A dirty furnace filter obstructs air and forces the furnace to work harder.

Tip

A clogged filter is a chief reason why a furnace may not be blowing hot air. It's also a reason why a furnace short-cycles (or turns off before the room reaches the set temperature).

A clean furnace filter is also important for indoor air quality. In the absence of standalone air filtration systems, the furnace acts as the home's de facto air filtration system.

Furnace filters with a MERV 13 rating are recommended by the EPA as being able to remove at least half of the very fine 0.3 to 1.0 μm particles that affect children, those with asthma, the elderly, or anyone with upper respiratory problems.

What Is MERV?

MERV, or Minimum Efficiency Reporting Values, rates the efficiency of furnace filters to filter out particulates between 0.3 and 10 microns (µm) in size. MERV ratings range from 1 to 16. Above MERV 16 is the highest level, HEPA (High-Efficiency Particulate Air).

When to Replace a Furnace Filter

Remove the current air filter and hold it up to an artificial light. If light clearly passes through the filter, the filter is still good. Even a light-gray air filter may still be good as long as the light is sharply visible.

If no light can be seen through the filter, discard the filter. If the filter is gray or clogged with hair or dust, also discard the filter and replace it with a fresh one.

When to Change the Filter More Often

You may need to change the furnace filter more than every three months if any of these conditions are present:

• Air return is located near a door

• Flat panel filter used instead of pleated filter

• Cold snap

• Pollen season

• Indoor construction

• Wildfires

• More occupants or pets in the home

Long vacations, periods between heating seasons, or any extended system downtime can reduce how often you need to change a furnace filter.

Cost to Change a Furnace Filter

Furnace filters generally cost $2 to $6 per filter. Flat panel furnace filters cost from $1 to $3 per filter and have MERV ratings of 1 or 2. Pleated furnace filters start at $6 and run up to $29 for MERV 8 to 13 filters.

Most homeowners can change their own furnace filter, so no labor charges are involved. However, changing the filter is usually included as part of an annual HVAC preventative maintenance visit—an average of $195 for the entire visit, not just the filter change.

Ways to Keep Your Furnace Filter Cleaner

• Clean the floor near the air return.

• Turn off the system to clean the air return.

• Add an air return filter to the grille.

• Shut off the furnace during dust-producing activities.

• Groom pets outside.

• Vacuum the air return grille frequently.

• Vacuum as far as possible in the air return duct with a household or shop vacuum extension.

• Have the furnace ducts professionally cleaned.

Tip

Regular furnace maintenance keeps the blower assembly cleaner. Located within the furnace, the blower assembly is difficult to access and should only be cleaned by HVAC technicians.

How to Change a Furnace Filter

1. Turn off the furnace: Turn the thermostat to OFF.

2. Find the filter: Locate the air handler section of the furnace.

3. Determine airflow direction: Before removing the filter, note the direction of the airflow by checking the arrow on the filter's cardboard frame.

4. Remove the filter: Slide out the current filter.

5. Check filter specs: Note the dimensions of the filter and use these to buy a new filter.

6. Insert the new filter: Slide the new filter in place, with the arrow pointing in the direction of the airflow.

7. Close the air handler cover: Close the cover tightly as the system needs to be airtight to operate properly.

Tip

Don't know the airflow direction? With the system running, detach the air handler cover. Do not reach inside. The filter will be pressed against the outflow side.

Read Next: 5 Common Problems With High-Efficiency Furnaces

Read the original article on The Spruce.