Furnace Filter Help: Your Guide to All Furnace Filter Questions

HVAC Logo IconBy HVAC.comAugust 1, 2023
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HVAC contractor installing furnace filter

The filter is an integral component of your HVAC system. There are a variety of sizes and options available – it’s no wonder homeowners have so many furnace filter questions! Below, find the furnace filter help you need to understand furnace filters, how they function, and how to choose the best one for your home and HVAC system.

Furnace Filter Questions: What are the different types of furnace filters?

Furnace filters are either disposable or washable. Disposable models are simply pulled from the unit and replaced with a new, clean filter as needed. Washable furnace filters are reusable – as needed, the filter can be removed from the filter cabinet, cleaned according to the manufacturer’s instructions, thoroughly dried, and reinserted in the filter cabinet to continue providing quality air filtration for the home.

Disposable furnace filter options include:

  • Fiberglass filters
  • Synthetic media filters
  • Polyester filters
  • Electrostatic filters
  • Pleated media filters
  • HEPA (high efficiency particulate arrestance) filters

Furnace Filter Questions: What does MERV mean?

MERV is the rating system that expresses the efficiency of a furnace filter, and stands for Minimum Efficiency Reporting Value. MERV ratings range from 1 to 16; the higher the MERV rating, the more efficient the filter at capturing contaminants of various sizes.

Filters rated MERV 8 through 12 offer excellent air filtration for residential homes. While you may think it’s best to purchase the highest MERV-rated filter possible, using these filters could actually restrict airflow through your HVAC system, causing comfort issues, increased energy consumption, and system breakdowns. If you have questions about which furnace filter is right for your home and HVAC system, contact a trusted local heating and cooling professional for assistance.

Furnace Filter Questions: How long do filters last?

The service life of furnace filters varies due to many factors. The efficiency rating of the filter greatly affects its lifespan; filters with higher MERV ratings typically last longer than lower rated, low efficiency filters.

Factors concerning your household also impact a furnace filter’s service life. In homes with pets or smokers, airborne contaminants exist at higher concentrations – filters need to be changed more frequently and become clogged faster because more contaminants exist in the home. If asthma or allergy sufferers live in the home, changing the filter more frequently can help reduce airborne triggers in the home and lessen the symptoms suffered.

HVAC system usage also affects the frequency which a filter needs changed. During the hottest months of summer and coldest parts of winter, the heating and cooling system is running more frequently than in the spring or fall. Air is circulating through the system and contaminants are constantly being removed from the air supply by the filter, causing it to clog faster. The filter will need to be changed more often during these periods to maintain indoor air quality.

Furnace Filter Questions: When do I need to change my furnace filter?

Keeping the above factors in mind, reference the following guide to determine when your furnace filter needs to be changed. The filter manufacturer will also specify how frequently it should be changed.

  • 1″ Furnace Filter: 1 – 3 Months
  • 2″ Furnace Filter: 1 – 3 Months
  • 3″ Furnace Filter: 6 – 9 Months
  • 4″ Furnace Filter: 6 – 9 Months
  • 5″ Furnace Filter: 9 – 12 Months
  • 6″ Furnace Filter: 9 – 12 Months

Some noticeable signs also indicate your filter should be changed.

  • The filter appears gray with dirt and debris visible on the filter’s surface.
  • You notice more dust throughout your home.
  • The furnace or air conditioner is running longer than it typically does.

Furnace Filter Questions: How do I find my size?

Your heating and cooling system is designed to work with a specifically sized filter. It is important to only use filters of the appropriate dimensions in your system.

Most filters have their dimensions printed on the frame, in length x width x height format. When purchasing a replacement filter, note these dimensions and select a model of the same. If the dimensions are not printed on the filter, locate the model number, which will allow you to look up the dimensions to find the right fit.

Furnace Filter Questions: What is the function of a furnace filter?

The furnace filter works to pull contaminants out of the air circulating in your home. As air circles through the ducts back to your heating or cooling unit, it passes through the filter. As air moves through, pollutants such as dust, pet dander, dirt, and mold spores are trapped by the filter; cleaner air then passes through to be conditioned by the HVAC system and is sent back to your home.

By keeping air cleaner, your furnace filter helps to keep the heating and cooling units cleaner, too. By catching contaminants, the filter allows cleaner air to pass on to the HVAC unit, so less dirt and debris will build up inside the unit. Dirt and debris accumulating within your heating and cooling unit cause the unit to operate less efficiently, burdening the system’s components and causing breakdowns. Using a clean furnace filter helps protect the sensitive components of your furnace, air conditioner, or heat pump, lowering energy bills and saving you the hassle and expense of HVAC repairs.

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