HEPA Filters in Forced-air Furnaces and Air Conditioning Systems

Reader Contribution by Troy Griepentrog

Our recent article about energy-recovery ventilators (Ventilate Your Home with Minimal Energy Loss) stated that using a “true high-efficiency particulate air (HEPA) filter” in your forced-air heating or air conditioning system would reduce allergens more effectively than regular filters. But reader John Alderman pointed out that this could be dangerous. So we went to the experts for their advice.

Mel Mossman, Chief Mechanical Engineer at RS Means, helps us explain:

For existing furnaces the manufacturer should be consulted as some residential systems may not have enough fan or motor capacity to accommodate higher efficiency filters. Specially designed and built HVAC systems may be equipped with true HEPA filters and the design may include pre- and/or post-filter pressure sensors to signal the need for filter replacement/maintenance. An alternative method sometimes employed, is to install a bypass system. This system is ducted into the return air plenum of the air handler or furnace and is equipped with an integral blower unit so that the furnace or air handler is not required to overcome the airflow resistance of the HEPA filter.

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