Not All Filters Are Created Equal

Forced-air heating, ventilating and air conditioning systems require effective air filtration for optimum energy efficiency, maintaining clean(ish) ductwork and promoting good indoor air quality. Air filters should be changed regularly. How often they need changing depends upon a number of factors including, but not limited to:
 
•          Presence of pets that shed.
•          Amount of carpeted 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. To operate efficiently, the air supplied is returned to the system for reconditioning, taking with it all the air particles and the occasional tumbleweed of pet hair many of us are familiar with.

This junk-laden air flows through a filter before reaching the HVAC equipment. For cooling, there’s typically an A-frame arrangement of what looks like car radiators. For heating, it’s typically a combustion chamber. Without a filter, the cooling coils would get clogged and the heating side would burn off anything in the air.
Air filters trap much of debris that otherwise would end up back in the house, stuck in ductwork, clogging HVAC equipment—or in our lungs.

But which air filter is right for your system? There are more choices than you can shake a stick at. Fortunately, there are just two overarching characteristics to look for:
 
•  Permanent or disposable.
•  Flat or pleated media (with a handy
     MERV rating).
 
Disposable filters are the most prevalent. Some in the flat media group look like they’ll stop only particles larger than a golf ball. They have flimsy cardboard frames and a thin, flat mesh that you can easily see through. They’re cheap, but 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. Pleated filters are generally better than flat.
The Minimum Efficiency Reporting Value is a rating system that tells you a filter’s effectiveness at trapping 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 air) 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 grab it online, check for recommendations. Otherwise, go with a decent pleated filter with MERV of three to five and check it once a month to see how it’s performing. Also check to see if the dust inside abates.
Spend a little more and breathe a lot easier with a regular schedule of air filter replacement—a simple change that pays big dividends.