Inputs

Units

Airflow (CFM or L/s)

Velocity preset

Min velocity (ft/min)

Max velocity (ft/min)

Shape

Results

Target	Round ∅	Rect ∅
Min velocity	-	-
Mid velocity	-	-
Max velocity	-	-

Eq. dia (rect @ mid): - in Nearest round (mid): -

Sizing uses area = flow / velocity. This tool does not compute friction loss; confirm against your friction-rate method.

Rectangular sizing (mid-velocity)

Width (in)

Height (in)

Area (in²)

If a fixed width is provided, height is solved from area; otherwise width/height follow the aspect ratio.

Superheat & Subcooling (quick)

Superheat

Input mode

Evap saturation temperature (°F)

Suction line temperature (°F)

Superheat: 0.0 °F

Subcooling

Input mode

Cond saturation temperature (°F)

Liquid line temperature (°F)

Subcooling: 0.0 °F

Pressures to saturation temperatures are approximated from small lookup tables with linear interpolation for convenience. Always verify with full P-T charts for the refrigerant and conditions.

Notes

Duct sizing: Area = Flow / Velocity. Round diameter uses D = √(4A/π). Rectangular width/height follow your aspect ratio or a fixed width. Equivalent round for a rectangle uses D_eq ≈ 1.30 (ab)^0.625 / (a+b)^0.25 (reference approximation).
Friction: This tool does not compute friction loss. Confirm final sizes with your selected friction rate and duct material per your method.
Charge: Superheat = LineTemp - SatTemp. Subcooling = SatTemp - LineTemp. Input saturation temperature directly or derive from pressure with a refrigerant P-T table.

HVAC Duct Sizer + Superheat/Subcool