VAV Box Calculator

Size VAV terminal boxes with min/max CFM, reheat capacity, and inlet sizing.

VAV Box Type

Zone Cooling Load (BTU/hr)

Zone Heating Load (BTU/hr)

Supply Air Temp (°F)

Room Temp Setpoint (°F)

Zone Floor Area (sq ft)

Zone Occupants

Minimum Flow Setting (%)

Maximum Cooling CFM

CFM (design airflow)

Minimum CFM

Inlet Size

inches (round)

Reheat Capacity

BTU/hr

Discharge Air Temp (heat)

°F

Inlet Velocity

ft/min

Ventilation Min CFM

CFM (ASHRAE 62.1)

Recommended VAV Box

VAV Box Sizing

Max CFM = Cooling Load / (1.08 x (Room Temp - Supply Air Temp))

Min CFM = Max CFM x Min Flow %

Reheat = 1.08 x Min CFM x (Discharge Temp - Supply Temp)

Cooling only VAV: Throttles airflow from max to min based on zone demand
Reheat VAV: Adds heating coil for zones that need heating at minimum flow
Fan-powered: Has a small fan to maintain minimum flow even when primary air reduces
Minimum flow typically 30-50% for reheat, 20-30% for cooling only

Duct sizing.

Fan laws.

ACH rates.

Cooling load.

ASHRAE rates.

Coil selection.