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What every Homeowner needs to know about Furnace Filters

Air Filter Maintenance Guide

Keep Your Air Filter Working Like New with Advice from Our Experts

Forced-air heating is the most popular method in the United States for keeping a home warm. An essential component of forced-air heating is the air filter. Originally, the purpose of air filters was to keep large dust particles from damaging the heating and cooling equipment. Today, however, air filters have tighter weaves designed to trap much smaller contaminants. The result is cleaner indoor air, fewer allergy issues, and healthier occupants.

Change the Filter Regularly

For optimal system health, remember to change your filter regularly. If you have central air conditioning, keep in mind that the same blower motor and ductwork circulate air in the summer, meaning you need to remember to change the air filter all year round. Usually, that means checking the filter monthly and changing it every six months or when the seasons change. Pet owners may also see a need to change the filter more frequent.

When choosing a filter your best bet is to pick a mid-range filter no higher than MERV 8, which can trap particles as small as 3 microns—such as hair spray, pudding mix, dusting aids, and mold spores. Remember though, if your furnace came with a MERV 1 to 4 filter, the equipment may require some modifications to perform well with a higher efficiency filter. Only a licensed HVAC contractor should perform such modifications.

Filter Efficiency

The American Society of Heating, Refrigeration, and Air Conditioning Engineers (ASHRAE) established a standardized method for testing air filter efficiency back in 1987 called Minimum Efficiency Reporting Value (MERV). All air conditioning and heater filters today are given a rating on the MERV scale, which ranges from 1 to 16. Technically, filters can also rate 17-20, but these are High-Efficiency Particulate Air (HEPA) filters and are not designed for use in residential heater and air conditioning systems.

Filters are rated on their ability to trap smaller and smaller particles. Different types of filters have different MERV ratings:

  • Electrostatic filters: MERV 1-4
  • Throwaway filters: MERV 1-8
  • Cartridge filters: MERV 5-8
  • Pleated filters: MERV 5-8
  • Box filters: MERV 9-16
  • Bag filters: MERV 9-16

Air Testing