MERV Rating

Definition

MERV is the filtration scale defined by ASHRAE Standard 52.2. It ranks filters by how well they capture particles at three size ranges: 0.3-1.0 microns (smoke, viruses), 1.0-3.0 microns (mold spores, pet dander), and 3.0-10.0 microns (pollen, dust mite debris). Each MERV step up means more particles trapped — but also more pressure drop across the filter, which affects how hard the blower has to work.

Typical Austin filter ladder: MERV 6-8 (basic fiberglass or pleated — minimal filtration, low resistance), MERV 11 (good for allergens), MERV 13 (excellent for cedar fever, mold spores, smoke; the highest most residential systems can safely run), MERV 14-16 (clinical-grade — usually needs an upsized return duct to avoid starving the blower).

For most Austin homes, MERV 13 in a 4-inch media cabinet is the right answer. The 4" depth gives the filter enough surface area to maintain reasonable airflow at high MERV.

Why it matters in Austin

Austin's airborne load is unusually high. Cedar fever from mountain cedar pollen runs December through February. Spring oak pollen runs March through May. Wildfire smoke from West Texas drifts in during dry summers. A MERV 13 filter handles all three — but ONLY if the system was designed for the static pressure that filter imposes. Dropping a MERV 13 into a stock 1" filter slot on a system designed for MERV 8 can cut airflow by 25%+ and ice up the evaporator coil.

The upgrade isn't just the filter — it's the cabinet, the return-air sizing, and confirming the blower can keep up. Cheap Cold Air evaluates the whole airflow path before recommending a MERV jump.