Select Good Air Filters and Pave the Way for Effective Replacements

• Select a filter with a MERV (Minimum Efficiency Reporting Value) of at least 6—which will trap particles as small as 1 micron.

Don’t skimp on the filter you select or specify for your forced air heating and cooling equipment. The very inexpensive fiberglass filters—a.k.a. “rock-stoppers”—are only effective in preventing large particles from being distributed on equipment coils. Higher efficiency pleated and electrostatic filters will stop much smaller particles and thus, not only protect the equipment but also help to improve indoor air quality.

• Post key homeowner information to help ensure effective filter replacements.

In addition to selecting an effective filter, it is essential to replace filters when they become dirty because buildup will restrict air flow and can damage the equipment. In furnaces, inadequate air flow can ultimately cause the heat exchanger to become too hot—potentially resulting in temperature limit switches to turn off the system or even cracking the exchanger. In air conditioning units, restricted air flow causes the opposite problems—coils which are too cold—causing ice buildup on the cooling coils. This in turn can lead to equipment damage and water leaks as all of the ice melts.

While the builder or HVAC contractor will install the initial filter, it will be the homeowner who continues this maintenance task. To avoid problems down the road and help ensure good performance, builders/contractors should clearly post this information at or near the filter location:

• Filter dimensions
• Initial filter resistance (in inches Water Column) at a specified cfm airflow

Believe it or not, providing this information instead of only the MERV rating gives the homeowner a better chance of maintaining a well-functioning filter and HVAC system. This is due to the fact that for a given MERV rating, different filters can have much different pressure drops depending on the velocity of the air flow and the thickness and surface area of the filter. If a builder/contractor wishes to provide a recommended MERV rating for replacement filters, it should be clear that the selected filter must also adhere to the pressure drop criteria as well. Also, be sure that filter replacement is clearly stated in the homeowner’s maintenance expectations.