HVAC Air Filters

An HVAC air filter goes inside the HVAC system or ductwork to help catch small particles from the air such as dust, pollen, and pet dander. By acting like a net, it traps them, protecting the HVAC equipment from debris while also removing these unwanted particles from the air we breathe. These filters are held in place with a plastic or metal frame but the filter is easily removable and usually looks like folded or pleated paper.

An air filter is important because it removes tiny, harmful particles from the air that can’t be seen. When pollen, dust, or pet dander are in the air, it can make breathing harder, especially for people with allergies or asthma. Air filters also keep dirt and debris out of the HVAC system to ensure proper functionality.

The most common materials air filters are made of include fiberglass, pleated cotton, cloth, or carbon. The case that holds the air filter in place within the HVAC system is typically made of metal or plastic. Consult your local Trane dealer for guidance on which type of filter is best for your system.

MERV stands for Minimum Efficiency Reporting Values and this value indicates how effective the filter is at trapping allergens and pollutants. The minimum size particle that a filter can trap is measured using a unit known as a micron. The smaller the particles that the filter can trap, the higher the MERV rating is. For example, a filter with a MERV rating of 1-4 will filter out larger particles like pollen and dust. One with a higher rating of 8-13 can greatly reduce some of the smallest particles like viruses and bacteria, up to 99.9%.

Most experts agree that the best MERV rating for a residential air filter is between 8-13. Filters in this range can trap pet dander, smoke, smog, and pollen to make indoor breathing easier even for those with respiratory conditions or who are susceptible to infection. Keep in mind that levels higher than this are typically reserved for hospital or commercial environments and may not be compatible with residential HVAC systems.

Yes—according to the Environmental Protection Agency, pleated air filters are more efficient and effective at removing pollutants and allergens from the air than their fiberglass counterparts because they have more surface area to capture particles. In addition to this, they typically have higher MERV ratings than fiberglass filters and can be recycled after use.

AC filters and furnace filters remove particles from the air. It doesn’t matter if it's an AC and furnace system, heat pump system, or dual fuel system as they are the same type of filter. All of these systems should have an air filter for the return airflow to the indoor equipment so that homeowners can replace the filters, when needed, for optimal performance.

The location of the air filter varies based on the type of HVAC system in place, but most commonly they can be found in wall or ceiling return grills located centrally in the home, at the HVAC system in a slot inside the unit, or in a slot in the adjacent ductwork next to the HVAC system. 

The filter can be located in the return grille/s, in a filter box accessory attached to the return duct, or in a filter rack located inside the inlet opening of the indoor equipment. An air handler or furnace could have an integrated filter rack, both located at the return air opening. Check out “Where is the Air Filter in My HVAC System” for more guidance.

Most air filters should be changed at least once every 90 days. Households with multiple pets, allergies, or other respiratory concerns may benefit from changing their filters once every 30 days instead. For specific recommendations on your filter maintenance schedule, consult your local Trane dealer.

Once you have removed the old filter, it’s time to put the new one in. You want to make sure that you put the filter in the right way. Look for the arrow on one of the sides (usually the top). Slide the filter in with the arrow pointing to the furnace (the arrow should point in the direction of the airflow). 

You can mark an arrow on your furnace with a Sharpie to help you remember which way to insert the filter. You can also mark the date on the filter, or use the filter reminder feature in the Trane Home app to remind you when to change it if your thermostat doesn’t notify you.

Proper maintenance of an air filter depends on the type of system that you have in your home, but most will require maintenance every 90 days. Some systems have washable air filters that can be washed and reused, but others are disposable. Check out our guide to cleaning and maintaining your HVAC air filter.

Trane Filters powered by FilterTime is a filter fulfillment service that delivers high-performance filters straight to your door with free shipping. By using the Trane Home app or visiting TraneFilters.com, you can make a one-time filter purchase or sign up for ongoing subscription options. 

No matter which you choose you’ll get the quality and innovation you expect from Trane with a full range of filter sizes and our high-quality 1” filters that are tested to our rigid performance criteria, with electrostatically charged fibers that efficiently capture microscopic airborne particles. Find Trane Filters online or contact your local Trane HVAC dealer.

Finding the right size air filter for your HVAC system varies based on the unique installation in each home. An HVAC pro decides which filter sizes are best suited for your system, home, and lifestyle during the installation phase. Because of this, the information cannot be found in a manual and cannot be provided without looking at your specific system. You may be able to simply pull the old filter out and make a note of the measurements.

If you are comfortable doing so, you can measure the air filter or the return opening to determine the size needed. Keep in mind that each air filter has two sizes: an actual size and a nominal size. The actual size reflects the true measurements of an air filter when measured. This is often a very specific number such as 11.5 x 11.5 x .7, whereas the nominal size is rounded up to make the process of buying air filters simpler. In this case, the nominal size would be 12 x 12 x 1 and would be the size you need to purchase.

Using the wrong size HVAC air filter can damage your system and allow harmful pollutants into your home. Check your old filter to see if the size is listed or contact your local Trane dealer for guidance.

Learn more about air filters in our HVAC 101 on HVAC system filters.