Sensible, Latent & Total Heat Calculator
Free psychrometric heat load calculator. Find sensible, latent, and total cooling load in BTU/h from CFM, temperature split, humidity change, and enthalpy change, plus sensible heat ratio.
How the heat load calculations work
Cooling and heating loads split into sensible (temperature) and latent (moisture) heat, which sum to the total load. Each has a standard-air formula:
| Component | Formula |
|---|---|
| Sensible | Qs = 1.08 × CFM × ΔT (°F) |
| Latent | Ql = 0.68 × CFM × Δgrains (grains/lb) |
| Total | Qt = 4.5 × CFM × Δh (BTU/lb enthalpy) |
And Qt = Qs + Ql.
The constants are all derived from standard air at sea level (0.075 lb/ft³): 1.08 = 0.075 × 60 × 0.24, 4.5 = 0.075 × 60, and 0.68 converts CFM and grains of moisture to latent BTU/h.
Worked example
1,200 CFM across a 20°F dry-bulb drop:
Qs = 1.08 × 1,200 × 20 = 25,920 BTU/h of sensible cooling.
Sensible heat ratio (SHR)
SHR = Sensible ÷ Total. A typical direct-expansion AC system runs an SHR of about 0.75–0.85 — most of the work is lowering temperature, with the rest removing moisture. Humid climates push SHR lower (more latent); dry climates push it higher.
The factors assume standard air at sea level. Above ~2,000 ft, apply an altitude density correction. Need moisture or enthalpy values? Read them from a psychrometric chart or use the Dew Point & RH Calculator; for airflow itself, see the CFM & Tonnage Calculator.
How FieldPad helps in the field
Break down the load here, then keep the numbers with the job. FieldPad logs your capacity findings against the equipment and the client and turns them into a documented estimate — offline, on your iPhone, with full history on one record.
Stop Re-Running These Numbers by Hand
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