Sensible Heat Calculator
The sensible heat carried by a flow of air or water — the HVAC load calculation, from flow rate and temperature rise.
The heating or cooling a duct actually delivers.
How the sensible heat calculator works
Sensible heat changes temperature without changing phase: Q̇ = ṁ c ΔT, with ṁ the mass flow rate. For air, mass flow is volume flow × density, and at standard conditions the whole thing collapses to a familiar shortcut: about 1.2 kW per m³/s per kelvin.
It is called sensible because you can sense it — a thermometer registers it. The energy that goes into humidity instead is latent heat, and in humid climates it can exceed the sensible load.
Formula: Q̇ = ṁ c ΔT = ρ V̇ c ΔT
Worked examples
| Inputs | Sensible heat load | Note |
|---|---|---|
| 0.5 m³/s of air at 20 K rise | 12,060 W | 12.06 kW |
| Water instead | 41,860,000 W | 41.9 MW — water carries far more |
| A domestic duct | 1,809 W | 1.8 kW |
FAQFrequently asked questions
What is sensible heat?
Heat that changes temperature, as opposed to latent heat, which changes phase or humidity.
What is the quick rule for air?
About 1.2 kW per cubic metre per second per kelvin, at standard density.
Why is water so much better at carrying heat?
Its density is 830 times higher and its specific heat four times higher — roughly 3,500 times more heat per unit volume.
Does this include humidity?
No. Removing moisture is a latent load, and in a humid climate it can exceed the sensible load. Total capacity is the sum of both.
Why do air ducts need to be so large?
Because air carries so little heat per unit volume. Delivering 12 kW takes half a cubic metre of air every second.
Where these figures come from
- NIST — CODATA 2018 fundamental physical constants — G, g₀, R, c
- NIST Special Publication 811 — Guide for the use of the International System of Units — unit conversions
- The Engineering ToolBox — material properties — specific heats, expansion coefficients, densities
- National Physical Laboratory — the UK's national measurement institute
Last checked: September 2026. Constants are the CODATA 2018 values; formulas are the standard textbook forms.