Filtration and HVAC Calculators and Formulas

Filtration & HVAC Formulas and Calculators

• Face Velocity Calculator

  v = Q ÷ A

  v face velocity, Q airflow, A face area

  Example: 2000 CFM ÷ 4 ft² = 500 ft/min.

  Open the face velocity calculator →

• Air Permeability Calculator

  R = q ÷ A

  R air permeability, q air flow through the sample, A test area

  Example: 12 L/min ÷ 20 cm² = 100 mm/s.

  Open the air permeability calculator →

• SCFM to ACFM Calculator

  Q_act = Q_std × (T_act ÷ T_std) × (P_std ÷ P_act)

  Q gas flow, T absolute temperature, P absolute pressure

  Example: 100 SCFM at 100 psig and 68 °F = 12.82 ACFM.

  Open the scfm to acfm calculator →

• Pipe Pressure Drop Calculator

  ΔP = f (L ÷ D) (ρ v² ÷ 2)

  f Darcy friction factor (64/Re laminar, Colebrook–White turbulent), L pipe length, D inside diameter, ρ density, v mean velocity

  Example: Darcy–Weisbach with the Colebrook friction factor.

  Open the pipe pressure drop calculator →

• Bubble Point Pore Size Calculator

  d = 4 k γ cos θ ÷ ΔP

  d pore size, k pore shape factor, γ surface tension, θ contact angle, ΔP bubble-point pressure

  Example: 30 psi with isopropyl alcohol gives 0.42 µm (k = 1).

  Open the bubble point pore size calculator →

Unit Converters for Filtration & HVAC

• Face Velocity & Air Permeability Converter – CFM/ft², L/(m²·s), mm/s, cm/s, ft/min
• Flow Rate Converter – CFM, m³/h, L/min, L/s, GPM, sccm, SLPM
• Pressure Converter – Pa, kPa, psi, bar, inH₂O, mmHg, torr, atm
• Area Converter – m², cm², mm², ft², in², test areas
• Heat Transfer Coefficient Converter – W/(m²·K), BTU/(h·ft²·°F), kcal/(h·m²·°C), U-value
• Mesh to Micron Converter – US sieve number (mesh) ↔ opening in µm, mm and inches, with the full ASTM E11 table.

Common Filtration & HVAC Conversions

• cubic foot per square foot per minute to liter per square meter per second
• liter per square meter per second to cubic foot per square foot per minute
• cubic foot per minute to cubic meter per hour
• cubic meter per hour to cubic foot per minute
• pascal to psi
• psi to pascal
• square meter to square foot
• square foot to square meter
• BTU per hour square foot degree Fahrenheit to watt per square metre kelvin
• watt per square metre kelvin to BTU per hour square foot degree Fahrenheit

Using these filtration and HVAC calculators

Airflow, face velocity and area are linked by one relation, Q = v × A. The face velocity calculator solves for whichever of the three you do not know, from a filter or coil face area, a duct size or a test head, and reports the result in fpm, m/s, cfm or m³/h.

Filter and fabric testing uses the same relation at a fixed pressure drop: air permeability is simply the face velocity through the sample. HVAC data usually quotes actual flow, while compressor and process data often quote standard flow, so the SCFM to ACFM calculator corrects between them for temperature, pressure and altitude.

For pore and particle sizes, the bubble-point and mesh-to-micron tools convert test pressures and sieve numbers into micrometres. Filter efficiency classes in ISO 16890 and EN 1822 refer to particle sizes in micrometres, so these conversions connect a measured medium to a rated filter grade.