HVAC Filtration Efficiency Calculator

MERV rating selection from particle size targets.

MERV rating (1–16)

Target particle size (µm)

System airflow (CFM)

Filter face area (ft²)

Tab to move between fields

Filtration efficiency (%)

Pressure drop (in. w.g.)0.27

Face velocity (fpm)300

Fan power increase (W)14.6

Annual energy cost ($)$15.31

E1: 0.3–1.0 µm (%)50

E2: 1.0–3.0 µm (%)85

E3: 3.0–10.0 µm (%)90

How to Use This Calculator

How the result changes with MERV rating (1–16)

MERV rating (1–16): MERV 8 = residential, 13 = commercial/IAQ, 16 = hospital.
Target particle size (µm): Particle diameter in microns. PM2.5 = 2.5, PM10 = 10, bacteria ~1, pollen ~10.
System airflow (CFM): Total HVAC system airflow in cubic feet per minute.
Filter face area (ft²): Total filter face area. Standard 20×20 = 2.78 ft², 24×24 = 4 ft².

Filtration efficiency (%): ASHRAE 52.2 minimum efficiency for the target particle size at this MERV rating.
Pressure drop (in. w.g.): Clean filter pressure drop at the given face velocity.
Face velocity (fpm): Air velocity through the filter face. Target 300–500 fpm for pleated filters.
Fan power increase (W): Additional fan power consumed by this filter's resistance.
Annual energy cost ($): Extra electricity cost per year from filter resistance at $0.12/kWh.
E1: 0.3–1.0 µm (%): Efficiency for finest particles (smoke, bacteria).
E2: 1.0–3.0 µm (%): Efficiency for medium particles (mold spores).
E3: 3.0–10.0 µm (%): Efficiency for large particles (pollen, dust).

Identify Input Parameters
4 parameters
MERV rating (1–16) = 13, Target particle size (µm) = 2.5, System airflow (CFM) = 1200, Filter face area (ft²) = 4 = 4 input(s) provided
Calculate Filtration efficiency
Filtration efficiency
85 = 85
Calculate Pressure drop
Pressure drop = baseDP * (faceVelocity / 500)
0.27 = 0.27
Calculate Face velocity
Face velocity = airflowCfm / filterAreaSqFt
300 = 300