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If you have a central air system for heating and cooling your home, then both your air conditioner and furnace will typically share the same air filter. Air filters have two main purposes, to improve air quality in your home, and also to prolong the life of your furnace and air conditioner. Air filters improve air quality by trapping air contaminants (pollen, dust, smoke, mold, etc.) and preventing these particles from entering your HVAC system. Clean air filters allow your furnace and air conditioner to work optimally.

Air filters need to be changed routinely. Overtime, the air filter collects dust, pollen and other particles and becomes dirty. A dirty filter leads to restricted air flow which can be detrimental to your furnace and air conditioning systems.

Air filters come in a range of types and sizes and MERV ratings.

The following is a quick guide of what you need to know about air filters.

Furnace Filter Ratings

Air filters have a MERV (minimum efficiency reporting value) rating. A MERV rating indicates how effectively it provides air filtration. Higher numbers indicate better filtration.
MERV 1 – 4
Primarily designed to keep the HVAC system clean,

  • Expect to filter:
  • Pollen
  • Dust mites

MERV 5 – 8
Offers improved filtration

  • Expect to filter:
  • Mold spores
  • Dust particles
  • Pollen

MERV 9 – 12
Consider this level if you have mild allergies or respiratory ailments

  • Expect to filter:
  • Auto emissions
  • Pet dander
  • Small airborne particles

MERV 13 – 16
Provides exceptional air quality

  • Expect to filter:
  • Pollen
  • Dust
  • Auto emissions
  • Pet dander
  • Small airborne particles
  • Mold
  • Virus
  • Bacteria spores

When to Change Your Air Filter

Air filters get clogged with air contaminants over time. Generally, air filters need to be replaced every few months. Usually filters will have an indication of how many months they should last. It is still a good idea to check your filter monthly or every other month to see if the filter is becoming clogged. Larger households, especially those with pets, may need to replace their filters more frequently.

Types of Air Filters

Air filters come in different materials, here is a quick reference for what you might expect from the more common types:
Fiberglass or synthetic: These are inexpensive and disposable.
Polyester: These filters are more effective at protecting against contaminants.
Electrostatic: These air filters come in washable versions and are longer-lasting.
Pleated: Pleated air filters provide improved results without compromising airflow.
HEPA (High-efficiency particulate air): HEPA filters effectively trap contaminants to create a healthy home environment

Air Filter Size

It’s important to know your air filter size prior to going to the store to purchase a new one. You can locate your air filter size by looking on your current air filter. If it is not marked, or no filter is in place, you can look online for your furnace model number and check for the air filter size recommendation. It is important to get the right size of air filter to avoid air flow obstructions and provide maximum filtration. Prior to taking out your air filter you’ll want to make note of which direction the air filter is placed. Usually arrows on the filter will indicate the direct of air flow. Some homeowners find it helpful use a Sharpie to mark on the outside of their furnace the direction of airflow, making future air filter replacements less of a headache.

If you need help installing a new air filter or want to schedule an annual furnace or air conditioner tune-up, which includes a standard filter change, give the HVAC experts at Black Diamond Heating and Air a call.