Whole-House Air Cleaner

A whole house cleaner is a filter cabinet built into the ductwork beside the air handler. Most hold a pleated media filter 4 to 5 inches deep, usually rated MERV 13. This is the ASHRAE scale where 13 captures roughly 85 percent of particles in the 1 to 3 micrometer band. Depth is the point. The extra media area means lower resistance and a 6 to 12 month life, against 1 to 3 months for the 1 inch filter it replaces. Higher end versions add a bypass HEPA module with its own booster fan.

Portable formats treat one room at a time and follow you around the house. A Portable HEPA Air Purifier reaches a bedroom in seconds; this style reaches every room but only through the ducts. An Electrostatic Precipitator can be installed in the same cabinet position and swaps filters for washing. What separates the ducted approach is that it cleans the air the heating and cooling system is already moving, with no box on the floor.

One limitation shapes everything: filtration happens only while the blower turns. In mild weather that may be two hours a day, which leaves the other 22 untreated. Switching the fan to continuous circulation fixes coverage and adds roughly 300 to 600 kilowatt hours a year with an older blower motor, considerably less with a modern variable speed one. Leaky return ducts undercut the whole exercise by drawing unfiltered attic or crawl space air in downstream of the filter, the same problem that defeats a new Central Air Conditioning unit bolted to old ductwork.

Fitting a cabinet means sheet metal work at the plenum, and any duct modification or new wiring belongs to a licensed trade. Check static pressure before choosing a filter grade, because dropping MERV 13 media into a system designed for MERV 8 can starve airflow enough to freeze the evaporator coil. Note the airflow arrow on the frame, seal the cabinet door so air cannot sneak past the filter, and change on schedule rather than when it looks grey. Keep a portable unit in the bedroom anyway for smoke events, since a ducted filter cannot deliver five air changes per hour to one room.