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Sensible, Latent and Total Heat Calculator

Enter the airflow and the air conditions before and after a coil (or just the temperature and moisture drop) to see how much of the load is sensible, how much is latent, and the sensible heat ratio.

Method reviewed October 26, 2026. Version 1.0.0. How it works

Your inputs

Unit system

Thinner air at altitude carries less heat per CFM. Leave at 0 for sea-level (standard-air) results.

Result

Sensible heat
27,000BTU/h
Latent heat
12,667BTU/h
Total heat
40,544BTU/h
Sensible heat ratio (SHR)
0.666

27,000 BTU/h sensible and 12,667 BTU/h latent: SHR 0.67.

Total heat
3.38tons
Show the working
  1. Humidity ratios and enthalpies (ASHRAE psychrometric equations)
    76.5 → 57.8 gr/lb; 31.18 → 22.17 BTU/lb
  2. Sensible = 1.08 × density ratio × CFM × ΔT
    1.08 × 1 × 1,000 × 25 = 27,000 BTU/h
  3. Latent = 0.68 × density ratio × CFM × Δgr
    0.68 × 1 × 1,000 × 18.63 = 12,667 BTU/h
  4. Total = 4.5 × density ratio × CFM × Δh
    4.5 × 1 × 1,000 × 9.01 = 40,544 BTU/h
  5. SHR = sensible ÷ total
    27,000 ÷ 40,544 = 0.666
  6. Note
    The 1.08 and 0.68 constants are rounded, so sensible + latent can differ from the enthalpy total by a few percent.

Sensible versus latent heat

Sensible heat changes the air temperature you feel on a thermometer. Latent heat is the energy tied up in water vapour: removing moisture from air takes energy even though the temperature does not change. A cooling coil does both, and the sensible heat ratio (SHR) is the share of its work that goes into lowering temperature.

A low SHR (for example 0.65) means a lot of dehumidification; a high SHR (0.85 or more) means mostly temperature drop. Humid climates need equipment and airflow that deliver a lower SHR.

The formulas

For standard air (0.075 lb/ft³) the familiar constants are:

  • Sensible heat = 1.08 × CFM × dry-bulb drop
  • Latent heat = 0.68 × CFM × drop in grains of moisture per pound of dry air
  • Total heat = 4.5 × CFM × drop in enthalpy (BTU per pound of dry air)

Each constant is 60 minutes × the air density, multiplied by the specific heat (1.08) or the latent heat of water divided by 7,000 grains per pound (0.68). At altitude the tool scales them by the air density at your elevation. When you enter temperatures and humidity, the humidity ratios and enthalpies come from the ASHRAE psychrometric equations, checked against PsychroLib.

Why the parts may not add up exactly

With full air conditions, total heat is taken from the enthalpy change, which is the more exact figure. Because 1.08 and 0.68 are rounded constants, sensible plus latent can differ from that total by a few percent. In the temperature-and-moisture mode, total is simply sensible plus latent.

Worked example

These are the example values the calculator opens with, and the result the engine calculates for them.

Inputs

I know
Entering and leaving temperature and humidity
Airflow
1,000 CFM
Entering air dry-bulb
80 °F
Entering relative humidity
50 %
Leaving air dry-bulb
55 °F
Leaving relative humidity
90 %
Site elevation
0 ft

Result

Sensible heat
27,000 BTU/h
Latent heat
12,667 BTU/h
Total heat
40,544 BTU/h
Total heat
3.38 tons
Sensible heat ratio (SHR)
0.666

27,000 BTU/h sensible and 12,667 BTU/h latent: SHR 0.67.

Assumptions

  • 1.08 = 60 × 0.075 lb/ft³ × 0.24 BTU/lb·°F, 0.68 = 60 × 0.075 × latent heat ÷ 7,000 gr/lb and 4.5 = 60 × 0.075 (standard air), each scaled by the air-density ratio at the site elevation.

Limitations

  • Steady conditions at one moment; readings must be taken in well-mixed air.
  • Uses rounded standard-air constants; for a measured coil capacity from wet-bulb readings use the Cooling Capacity Calculator.

Frequently asked questions

What changes a system’s sensible heat ratio?

Airflow, coil temperature and the humidity of the entering air. A colder coil (for example from lower airflow per ton) removes more moisture and lowers the SHR. Use the manufacturer’s performance data for a specific system.

Can latent heat be negative?

Yes. If the leaving air holds more moisture than the entering air, as in an evaporative cooler or humidifier, the latent value is negative and the SHR can exceed 1.

How is this different from the Cooling Capacity Calculator?

The Cooling Capacity Calculator works from wet-bulb readings taken in the field. This tool accepts relative humidity or the moisture difference directly and focuses on the sensible-latent split.

Sources

  1. Regional Line Card — air-side formulas — Trane. Sensible = 1.08 × CFM × ΔT; latent = 0.68 × CFM × Δgr; total = 4.5 × CFM × Δh, with the derivation of each constant.
  2. PsychroLib — psychrometric functions after ASHRAE Handbook—Fundamentals (2017) ch. 1 — PsychroLib (open source, MIT licence). Humidity ratio W = 0.621945·pw/(p − pw), wet-bulb, enthalpy and standard-atmosphere equations as published by ASHRAE.

Spotted an error? Report a problem with this calculator — see our corrections policy.