What this calculator does
Air handling loads arrive in two parts. The sensible part is the heat you feel; the latent part is the moisture removed by dehumidification. This calculator splits an airflow and its temperature and humidity differences into those two components and expresses the total in tons of cooling.
How to use it
- Enter the airflow in cubic feet per minute.
- Enter the dry-bulb temperature difference the air experiences across the coil.
- Enter the humidity-ratio difference in grains per pound of dry air.
- The sensible and latent loads are reported separately so you can size the coil and the dehumidification separately.
Governing formula
Q_s = 1.08 · CFM · ΔT ; Q_l = 0.68 · CFM · ΔW Where:
-
ΔT= Dry-bulb temperature difference [°F] -
ΔW= Humidity ratio difference [grains/lb]
Worked example — 2,000 CFM with a 20 °F and 30 gr/lb duty
The figures below were produced by running this page's own engine with the example inputs (Airflow (CFM), Sensible temperature difference (°F), Humidity ratio difference (gr/lb), Unit system). If the calculator returns something different for the same numbers, that is a bug, not a rounding difference.
| Sensible load | 43200 Btu/h |
|---|---|
| Latent load | 40800 Btu/h |
| Total load | 84000 Btu/h |
| Equivalent capacity | 7 tons |
| Basis | Constants assume standard air (0.075 lb/ft³); the latent transfer uses 0.68 Btu·min/(lb·grain). |
- Sensible: 1.08 × 2,000 × 20 = 43,200 Btu/h.
- Latent: 0.68 × 2,000 × 30 = 40,800 Btu/h.
- Together 84,000 Btu/h is 7 tons of cooling — note how much of the duty is latent, which is common in humid climates.
Assumptions & limitations
Engineering calculation. Uses the standard air-transfer constants (1.08 sensible, 0.68 latent per CFM of standard air). Psychrometric properties are assumed rather than calculated from a coil condition.
- Constants assume standard air at 0.075 lb/ft³; high-altitude or hot-humidity conditions need density corrections.
- No coil bypass factor, condensate load or part-load humidity ratio is modelled.
- Enter the difference the coil actually has to remove, not the room setpoint to supply-air setpoint difference.
This tool supports professional engineering work; it does not replace a sealed design. Confirm every result against the applicable standard and a licensed engineer before it is built.
References & standards
- ASHRAE Handbook — Fundamentals, psychrometrics and air-conditioning load processes.
- ACCA Manual J — residential load calculation.