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Air filters are a big component of the overall health and longevity of your HVAC system. They filter out dust, pollen, and pet dander. They protect your system from dangerous objects like loose insulation that can be pulled into the system and create a fire risk. Some filters trap mold spores and bacteria, preventing them from being cycled back into the air you breathe.

Unfortunately, filters are very much out of sight and easily out of mind. If you’re not maintaining the filters in your house and regularly changing them, they no longer protect you and can damage your system. Clogged air filters are one of the most common reasons for emergency repair and HVAC system failures.

We’ll cover everything you need to know about changing the filters in your home, so you can rest (and breathe) easier.

Where are air filters located?

Most residential HVAC systems have a filter located in either the central air return unit (typically in a garage or basement) or at the return vents. Return vents are large metal grates, typically installed under stairwells, in hallways, or other big open areas of the house. They pull air through the ductwork and into the heating and cooling unit. The return vents are places where airflow is going into the system, not out.

How do I replace my air filters?

First, you’ll need to figure out the right filter size.

  • Check the label on the dirty filter’s frame, typically printed along one of the edges.
  • Use a tape measure or ruler to measure the filter’s length, width, and depth (thickness). Round up to find the correct filter size.
  • Measure the length, width, and depth of the inside edge of the return vent. Get a filter that is slightly smaller (by about .25”-.5”).

If the return air vent has a filter slot, installing a new filter is simple. Just slide the correctly sized filter into the component slot with the arrow pointing in the direction of airflow. For example, if you’re replacing a filter for a return vent, the arrow will point away from you when you’re facing the vent.

Cut-to-fit filters tend to be a little more difficult to install. You will need to turn off the system, open the vent grille, and clean the duct of any debris. Measure the vent size and cut the filter accordingly. Tape the filter into the grille. Double sided tape can is a great tool for this step.

How often should I change my air filters?

Different houses and lifestyles call for different timelines. If your house has more people in it, pets, or family members with respiratory issues, you will most likely need to change the air filters more often. That being said, you should check your filters once a month, changing them every 30-90 days.

The type of filter used will also impact how often they need to be changed. It’s important to install a filter with the correct thickness for your unit. Too thick might restrict the airflow and overwork the system, while too thin will get dirty must faster than expected, clogging airflow.

What happens if I don’t change my air filters?

As the filters in your home do their job and trap particulates, there is less space for air to freely pass through the filter and into the heating and cooling unit. The system works harder to pull enough air into the unit to heat and cool your home. A system with dirty filters can’t function like it’s supposed to, and the consequences of that can be expensive and time-consuming.

  • Poor air flow impacts temperature sensors and your home temperature isn’t correctly regulated.
  • Energy bills increase due to an overworked system.
  • Poor air circulation causes dust build up, leading to more dusting and allergies for your family.
  • Moisture on the material encourages bacteria and mold growth, which is circulated through your home.
  • Extra wear and tear on the HVAC unit causes more breakdowns and system failure, resulting in costly repair and replacement bills.

Can I run my system without air filters?

Technically, an HVAC system can run without filters for a short period of time, but we strongly advise against it. The biggest problem is that a lack of filters opens your system up to dangerous debris that creates fire hazards. Particulates will be blown back into your home and the air you breathe, contributing to health problems and allergies. Unusually dusty blower fans wear out and malfunction faster, using more energy and breaking down much sooner.

Just because your system theoretically can run without a filter, doesn’t mean it should. If your home currently doesn’t have a filter, we recommend installing one as soon as possible and scheduling an HVAC technician to inspect your system.

Indoor air quality and lifespan of your HVAC system rely on clean filters.

Dirty air filters won’t impact your system immediately, but over time you will notice a difference in air quality, energy bills, and repair costs. It’s easy for filters to fall to the back of the priority list, but by maintaining your filters you will extend the life of your system and preserve good air quality for your family.

Please note that changing your air filters on a perfectly timed schedule won’t help if your ductwork isn’t sealed correctly or the system has cracks and holes. If you’re properly changing out your filters and you feel that your system isn’t functioning like it should, contact a professional.

(208) 274-9938