Equipment protection
Thin fibreglass filters. They keep lint and large dust off the blower and coil, but do little for the air you breathe.
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- Filter ratings
MERV ratings, explained on one scale.
Air filters are rated from MERV 1 to MERV 16 under the ASHRAE 52.2 test. Higher ratings catch smaller particles — but they also resist airflow more, and not every system can cope.
The MERV scale
The common home filter
Pleated filters that catch dust, pollen, dust mites and mould spores. A sensible minimum for most homes.
A step up
Catch more of the finer dust and allergens. A good upgrade for allergies — if your system has the airflow to spare.
Fine particles and smoke
Catch a large share of fine particles, including wildfire smoke. The EPA suggests MERV 13 or higher where the system can take it; many need a deeper filter cabinet first.
A general guide to what each range is designed to catch — not a test result for any product.
Can your system take a higher rating?
A denser filter makes the blower work harder. In a system with small return grilles or a thin 1-inch filter slot, a MERV 13 filter can cut airflow enough to freeze the coil or overheat the furnace.
- A 4- or 5-inch media cabinet lets a high-MERV filter breathe.
- We measure static pressure before and after, so we know the system is happy.
- California's energy code now calls for MERV 13 filtration on the systems in new homes.
For homes and businesses
At home: most houses do well with MERV 8–11 changed on time, and MERV 13 in a proper cabinet for allergies or smoke season.
For businesses: rooftop units often take MERV 13 filters in banks. We match the filter to each unit and change them on a schedule, with a note of what was fitted.