Air Distribution
Air Distribution Tools
Practical calculators for airflow, velocity, air changes, friction rate, pressure, and duct-system design.
Q = V × A
Airflow, velocity & area
CFM
FPM
Cross-sectional area perpendicular to the direction of airflow.
ft²Round geometry
in
Calculated area: —
Rectangular geometry
in
in
Calculated area: —
Calculated results
Air relationship
Airflow
—CFMVelocity
—FPMArea
—ft²Area
—in²Uses cross-sectional area only. No duct-equivalency or automatic sizing factors are applied.
Units & Terms
Quick reference for abbreviations and units used in these calculators.
- CFM
- Cubic Feet per MinuteVolumetric airflow rate.
- FPM
- Feet per MinuteAir velocity.
- ACH
- Air Changes per HourThe number of times a space's air volume is replaced in one hour.
- ft²
- Square FeetCross-sectional area, such as duct area.
- ft³
- Cubic FeetVolume, such as room volume.
- in. w.g.
- Inches of Water GaugePressure measurement commonly used in HVAC systems.
- in. w.g./100 ft
- Pressure Loss per 100 Feet of DuctDuct friction pressure loss expressed per 100 feet.
- SP
- Static PressurePressure exerted by air within an HVAC system.
- ASP
- Available Static PressureStatic pressure available to overcome distribution-system pressure losses.
- ESP
- External Static PressureStatic pressure external to the HVAC equipment used when evaluating the available pressure for the distribution system.
- TEL
- Total Effective LengthEffective duct-system length used for friction-rate calculations, including the effect of fittings where applicable.