How Often Should You Change Your HVAC Filter? A Short Guide

Changing your air filter benefits your HVAC system, from maintaining clean indoor air to improving overall functionality. It can also prevent allergens and musty odors from flowing inside your home.

As the seasons change in Illinois, so should your air filter. As Niles’ trusted HVAC company, A Custom Services knows when system adjustments become necessary. Read more to learn when and why you should change your HVAC filter.

How Air Filters Help Your Air Quality

Manufacturers make air filters from fiberglass or pleated paper and give them a cardboard filter frame to stabilize their form. They usually go in the return vents, where air leaves the rooms and returns to circulate in the system.

Air filters serve as a protective barrier between your HVAC system and harmful airborne particles, such as:

  • Dust
  • Dirt
  • Human and pet dander and hair
  • Mold
  • Lint
  • Pollen
  • Bacteria

Most air filters come with a minimum efficiency reporting value (MERV). The MERV rating helps determine what size and kinds of pollutants the air filter blocks. Its ratings range from 1 to 20, with higher numbers depicting filters that block smaller particles.

Filters rated MERV 16 and below generally meet residential air quality maintenance requirements. MERV 17 through 20 refers to a medical-grade type called a high-efficiency particulate air (HEPA) filter. These filters typically clean and protect the air in hospitals and surgical rooms.

MERV Ratings and Your HVAC System

While you may think higher MERV ratings always indicate better quality, that may not be the case. Larger numbers indicate smaller pockets and divots for the filter to catch particles. Airflow also decreases for these numbers because of the smaller mesh.

Some systems cannot handle or work with reduced airflow, which could damage them. An inappropriate air filter can do about as much harm as a dirty filter. For example, a MERV 16 filter would seem like a blockage in air conditioners meant for MERV 11 filters.

You should review your product manual to find which MERV rating you need when changing your HVAC filter. Otherwise, you may experience decreased indoor air quality and temperature control. Your system lifespan can also lessen because components, like the blower fan, overwork to compensate for the lack of air.

What About Furnace Filters?

Some people may use air filters and furnace filters interchangeably. While similar products, these filters have different qualities that optimize them for the environments they cleanse.

Although both filters use MERV ratings, their thickness and materials may differ. Air filters have optimal materials for cool and warm air, while furnace filters have the quality to withstand high temperatures. Furnace filters also tend on the thicker side, up to several inches, while most air filters use thinner mesh.

If searching for a filter on your own, specify whether you seek an air filter or a furnace filter. The wrong filter can damage the HVAC system and may catch fire. If unsure how to spot the difference between the types of filters, always ask for help or hire an experienced HVAC specialist.

Ensure You Change Your Filter on Time

Most companies advise that you change your HVAC filter roughly every 90 days or three months. You may want to shorten the time depending on climate conditions or if you have pets or ill family members. Vacation homes and locations lacking foot traffic can last several months without a filter change.

For furnace filters, it depends on the thickness. Ones up to two inches thick need a replacement every one to three months. Thicker furnace filters can last for up to nine months.

When you fail to change the air filter, you decrease the quality of the air you breathe. However, air filters mainly protect your HVAC system from debris and buildup. Without a filter change, your system can clutter, slowing and clogging internal components.

Your HVAC system slows down and fills with pollutants, leading to allergen development and poor temperature control. If the system breaks down, you could pay hundreds of dollars for costly repairs and replacements.


The experts at A Custom Services Inc. can monitor your HVAC system condition, from the refrigerant to the air filter MERV ratings. With our technicians on the job, you do not need to worry about when to change your HVAC filter. Our top-notch services run 24/7 in the Chicago, IL, area.

Call us at 773-207-7551 for a free estimate on your residential and commercial HVAC system needs today!

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