Heating & hot water
Power for target recovery time
- where
- required power (W; the calculator shows kW)
- fluid density (kg/m³)
- heated volume (m³; any unit you pick is converted)
- specific heat capacity (J/(kg·K); any unit you pick is converted)
- water temperature rise (K)
- target time (s; any unit you pick is converted)
Explain this equation
Works out the heat input needed to heat a cylinder through a given rise in a target time. Use it to judge coil, boiler or immersion size for a recovery target.
ρ × V × c_p × ΔT is the energy needed to heat the stored volume through the rise. t is the time you want it done in.
Power is energy divided by time. The calculator works in watts and shows kW.
Sense check: 150 L through 50 K in 30 minutes needs about 17.4 kW of useful heat into the water. Halve the time and the power doubles.
Watch out: this is the useful heat reaching the water. Boiler input will be higher once efficiency is allowed for, and the coil must actually be able to transfer that power.
Enter your values to see the result.
Good to know
Ideal water heating. Boiler input, coil capacity and safety design need separate checks.
Sources
Results are arithmetic only. Worked examples are not recommended design settings. This library does not provide automatic gas pipe selection, live gas tightness tests, purging procedures, combustion acceptance limits, installation approval or commissioning certification. Manufacturer data and the applicable current method remain essential.