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What’s With All These Filters?

By Tom Tate

When it comes to energy conservation and home maintenance, it seems like the choices grow and grow with each passing year as evidenced by light bulb choices (see the article in the January edition), the plethora of thermostats and now, air filters. Why so many? It comes down to providing choice between cost, performance and longevity.

Filters today range from the inexpensive fiberglass variety using material that looks like the handiwork of frenzied spiders to the high efficiency particulate arrestance (HEPA) variety – $30 and up — for the ultimate in residential air filtration. Also available for your consideration are washable, electrostatic and other choices.

The most affordable are the flat filters. They are usually made of fiberglass and are the least effective in trapping particles of dirt and dust. When I pulled the flat filter I was using from my system, there was barely anything on it. Pleated filters are next and because the pleats offer more surface area, they are far better at trapping airborne debris. This type replaced my flat filter. When it was time to change, it had substantially more dust and debris, obviously a better performing product. Having said that, as long as you are replacing the filter on a monthly basis and do not have severe allergies, the fiberglass, flat filters absolutely do the trick.

HEPA filters are the most effective and are usually marketed as pollen / allergen reducers. For a person with seasonal allergies, these may be a good choice. Marketing names attempt to help buyers pick the proper filter. A better option is to use the industry rating system called MERV,minimum efficiency reporting value, running from 1 to 12 with 12 trapping the most (and smallest) particles. MERV is intended to allow comparison of competing filters.

Some filters have an electrostatic charge which are designed to attract more dirt particles and others are permanent or washable. Based on personal experience, they don’t seem to be much better but as the folks who advertise financial products like to say, “Your results may vary.”

A word of caution is offered in closing. Depending upon the type, age and sophistication of your system, installing a filter with a high MERV rating may not be the best idea. Keep in mind here that this higher MERV rating does not result in a more energy efficient system. Installing a high efficiency filter in your system can cause it to be less energy efficient. Why? The filter restricts air flow and increases static pressure that the blower must overcome to move air. In other words, your HVAC system has to work harder. And, as the high efficiency filters collect dirt, the impact on energy use grows. My suggestion is to take a slow approach and keep an eye on energy use to see if your system reacts negatively or positively to the higher efficiency filter.

Proper filter use is an essential part of your HVAC system upkeep. Check out our article on maintenance this month for more on this topic.