Furnace air filters: everything you need to know

By HVAC.com•August 1, 2023

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Furnace air filters are a critical component of your heating system. You should replace yours at least once every three months.

In this piece, we’ll help you select the best furnace filter for your needs, explain how to change yours, and describe how furnace filters work.

Furnace Air Filters - Everything You Need To Know

What are furnace air filters?

Furnace air filters usually consist of a cardboard frame, a fiberglass filter, and metal mesh. The frame and mesh exist to strengthen the filter.

Furnace filters improve air quality in your home and protect your HVAC components from dust and debris. Without a filter, your HVAC equipment would become dirty, negatively affecting its performance (and likely increasing your utility bills).

The filter catches and traps contaminants as air passes through your heating system. If you don’t replace or clean your filter regularly, it could restrict airflow and damage your HVAC equipment.

How often should you replace your furnace air filters?

In most cases, you should change your furnace filters every three months. However, there are some situations when you may want to change your filter more or less often.

Change your filter MORE often if:

You have multiple pets
You or your family members have respiratory challenges
You live in an area with high pollution
You’ve recently remodeled or done construction in your home

Change your filter LESS often if:

The home is a vacation property that’s not always inhabited
Your furnace takes super-thick filters (3+ inches)

How do you replace furnace air filters?

Furnace air filter replacement is a job you can DIY. Follow the instructions below.

1. Find the filter compartment. It’s usually between the return air duct and the furnace.

2. Open the filter compartment door.

3. Slide out the used filter and dispose of it.

4. Unwrap your new furnace filter and slide it into the filter compartment. Position it using the printed arrows on the frame as a guide.

5. Replace the filter compartment door.

Types of furnace air filters

There are many variables to consider when choosing your furnace air filter replacement. Our article on the best air filters for your lifestyle can help you choose the ideal one for your needs.

When purchasing furnace filters, you’ll see the following attributes on the packaging:

📏 Size	Furnace air filters come in a variety of sizes. Make sure you purchase one that matches the size of your existing filter. You can learn more in our helpful guide on common air filter sizes.
💨 MERV rating	A furnace filter’s MERV rating indicates the granularity of particles it can trap. We recommend a filter with a MERV rating of 8 or above. However, you should always check your user’s manual for the manufacturer’s suggested MERV. Too high a MERV can restrict airflow. Too low a MERV can leave your system vulnerable to dust and dirt.
🧵 Material	We think pleated electrostatic filters are the best. Compared to synthetic fibers, electrostatic materials help attract more harmful particles and are more durable. Pleated filters are more effective because they have a larger surface area to capture dust and debris.