Sensible Load CFM - HVAC Calculator Toolbox

About this calculator This calculator determines the supply airflow required to offset a known sensible load, in either heating or cooling mode, given the supply (unit leaving) and space temperatures. It applies a density correction for altitude so results remain accurate at elevation. Use it when sizing supply air for a design load with a specific leaving air temperature target — the calculator works equally well for cooling (leaving temperature below space) and heating (leaving temperature above space) by using the magnitude of ΔT.

Use when You need to size supply airflow for a known sensible load at a given supply and space temperature.

Formula CFM = Sensible Load ÷ (1.08 × Density Factor × |ΔT|)

Variables

Sensible Load Sensible heating or cooling load in BTU/hrUnit Leaving Temperature Supply air temperature leaving the cooling or heating unit, in °FDesired Space Temperature Design indoor temperature in °FAltitude Installation altitude in feet — adjusts for air density

Sensible Load (BTU/hr)

Sensible heating or cooling load in BTU per hour

Unit Leaving Temperature (°F)

Temperature of air leaving the unit

Desired Space Temperature (°F)

Target indoor space temperature

Altitude (ft)

Installation altitude — autofilled from weather station

ΔT (°F) —

CFM —

How is supply airflow determined from a sensible load?

The sensible heat equation relates airflow to heating or cooling capacity: Sensible Load (BTU/hr) = 1.08 × CFM × Density Factor × |ΔT|, where ΔT is the difference between supply (unit leaving) and space temperature and Density Factor adjusts for altitude (1.0 at sea level, lower at elevation). Rearranging: CFM = Sensible Load / (1.08 × Density Factor × |ΔT|). The 1.08 constant combines standard air density (0.075 lb/ft³), specific heat (0.24 BTU/lb·°F), and 60 min/hr. A larger ΔT requires less airflow to offset the same load, but supply air that is too cold can cause drafts (cooling) or excessive stratification (heating). Typical design ΔT for comfort cooling is 15–25 °F; for heating it ranges 15–60 °F depending on the system type.

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