Frequently Asked Questions about Furnace Filters

1. Question: Does my furnace have a filter?

Answer: That depends on what type of furnace you have. If you have a warm air furnace then you have an air filter. If you have a boiler and radiators then you probably don’t have air filters.

2. Question: What is the purpose of a furnace filter?

Answer: Furnace manufacturers put inexpensive fiberglass filters into their furnaces to remove airborne particles that might damage the fan and the heating coil. Particle buildup can also decrease the efficiency of your furnace, as the furnace has to work harder to pull air through the intake. More expensive filters can also improve the air quality in your house by removing pollen, bacteria and mold spores from the air. This is especially important if you or someone in your family suffers from allergies.

3. Question: How often do I need to change my furnace filter?

Answer: Check the documentation that came with your furnace. Recommendations vary based on a number of factors: the type of filter that you use, how many pets you have, whether anyone in your home has allergies, etc. If you use disposable fiberglass panel or electrostatic panel filters, you should change them anywhere from once a month to once every three months. Pleated filters generally last from 3 months to a year. Filters are relatively inexpensive and easy to change, so there is little reason to wait. If you don’t change or clean your filter often enough the filter can get clogged with dust and other airborne particles, forcing your furnace to work harder to maintain airflow. This will reduce your furnace’s efficiency and can cause damage.

4. Question: Do I have to use a filter that is manufactured by the same company that makes my furnace?

Answer: Generally you can buy your filter from any source. Check with a filter vendor or the documentation that came with your furnace to be sure.

5. Question: How do I determine which filter to buy for my particular model of furnace?

Answer: Check the documentation that came with your furnace. However, sometimes those manuals seem like they were written by teenage chimpanzees. If you aren’t sure, ask us.

6. Question: What is a high efficiency filter, and do I need a high efficiency filter if I have a high efficiency furnace?

Answer: Filter efficiency refers to the percentage of airborne particles that the filter removes. This is different from the fuel efficiency of your furnace (commonly measured as the AFUE). You can choose either a high-efficiency or a low-efficiency filter for your highly fuel efficient furnace. (Note, however, that failing to change / clean your filter regularly can reduce your furnace’s fuel efficiency.)

7. Question:What is a MERV rating?

Answer: MERV stands for the Minimum Efficiency Reporting Value, and is a measure of a filter’s worst-case efficiency performance. The higher the MERV rating, the more efficient the filter.

Do you have more questions about furnace filters? Please see our filters home page.

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