MERV (Minimum Efficiency Reporting Value) is a 1-16 scale defined by ASHRAE Standard 52.2. It measures the percentage of particles in three size ranges (0.3-1 micron, 1-3 micron, 3-10 micron) that a filter captures.
- MERV 6-8: large particles — dust, lint, large pollen. Most basic 1-inch filters.
- MERV 11: small pollen, pet dander, mold spores. A common upgrade tier.
- MERV 13: bacteria, smoke particles, virus carriers. The CDC's recommended residential floor since 2020.
- MERV 14-16: clean-room grade. Usually too restrictive for residential equipment.
Higher MERV catches more, but also restricts airflow more. A 1-inch MERV 13 filter in a system designed for MERV 8 will create excessive static pressure and shorten equipment life. The proper upgrade path is a 4-inch or 5-inch media cabinet with the same MERV rating but 3-5x the surface area.
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