Not all air filters are created equal

Posted on Jul 27 2018 in Fulton County REMC

Greg Bitterling

I have had members ask me “how often should I change my air filter?” I’ll answer this question below. If you still have questions, give me a call at 574-223-3156 or 1-800-286-2265, and we will be happy to help you.

Forced heating, ventilating and air conditioning (HVAC) systems require effective air filtration for optimum energy efficiency, maintaining clean(ish) ductwork and good indoor air quality. Air filters should be changed regularly. How often? That depends upon:

  • Presence of pets that shed
  • Amount of carpeted vs. hardwood floors
  • Where you live — amounts of dust, pollen, etc.
  • Use of wood-burning supplemental heat sources
  • Presence of cigarette smoke

The air inside our homes is full of particles originating from inside and outside sources. As the name “forced air” implies, conditioned air is blown into the house through ductwork. In order to operate efficiently, the air supplied is returned to the system for reconditioning, taking with it all the particles in the air and the occasional “tumbleweed” of pet hair.

This junk-laden air flows through a filter before encountering the HVAC equipment. For cooling, there is usually an A-frame arrangement of what looks like car radiators. For heating, it is generally a combustion chamber. Without a filter, the cooling coils would get clogged and the heating side would burn off whatever was in the air.

Air filters trap a lot of debris that otherwise would end up back in the house, stuck in ductwork, clogging HVAC equipment – or in our lungs. But enough with the HVAC and air quality primer, let’s tackle types of air filters.

You have so many options with filters. Fortunately, they can be broken down into two nicely defined categories, making the selection process manageable. The two are:

  • Permanent or disposable
  • Flat or pleated media (with a handy MERV rating)

Disposable are the most prevalent. Some in the flat media group look like they will stop only particles larger than a golf ball. They have flimsy cardboard frames and a thin, flat mesh you can easily see through. While they are cheap, don’t waste your money. Your HVAC system and lungs deserve better.

Pleated filters perform better using media you cannot see through. While they look impervious, air can move through under pressure leaving its airborne cargo trapped.

Remember MERV? This rating system that stands for Minimum Efficiency Reporting Value tells you how effectively a filter traps particles. The scale runs from one to 16 (higher is better) and is based on trapping particles 3-10 microns in diameter. Research shows that residential filters with a MERV rating between seven and 13 are likely to be as effective as true HEPA (high-efficiency particulate arrestance) filters. This class of filter is used in clean room manufacturing and at the extreme end can trap particles much smaller than the diameter of a human hair, as small as 1 micron.

So, should you jump in and grab a supply of high MERV filters? Not without some research. All filters increase resistance to air flow. HVAC systems are designed to operate at a particular pressure and should support MERV ratings of one to four. A higher MERV value increases resistance, making the system work harder. It loses efficiency and increases wear on operating components.

So, how do you decide which level of filter to use? If you have your system’s operating manual or can find it online, check for recommendations. Otherwise, my advice is to go with a decent (MERV three to five) pleated filter and check it once a month to see how it is performing.

Spend a little more and breathe a lot easier with a regular schedule of air filter replacement — a simple change that pays big dividends.

Greg Bitterling
Member Services Manager and
Energy Advisor at Fulton County REMC