Energy to Heat Water Calculator
This energy to heat water calculator shows the heat needed to warm a substance: enter mass and temperatures, read off the energy in kWh and estimate heating time and cost.
Example: Substance: Water · Mass 200 kg · Starting temperature 10 °C · Target temperature 60 °C · Heating power (optional) 3 kW · Efficiency 90 % · Energy price per kWh (your currency) 0.2 per kWh → Heat energy: 11.61 kWh (41,813 kJ). Source: Wikipedia – Spezifische Wärmekapazität: Q = c · m · ΔT and table values. Updated: .
How it is calculated
Heating 200 litres of water from 10 to 60 °C takes about 11.6 kWh. The heat is the energy a substance absorbs when it warms by a given amount.
How it is calculated
The rule is Q = c · m · ΔT: specific heat capacity times mass times temperature difference. Water has c ≈ 4.18 kJ/(kg·K), aluminium 0.897, iron 0.449 and copper 0.385. The calculator divides the result in kilojoules by 3600 to get kilowatt-hours. Efficiency gives the energy you actually have to supply, heating power gives the time and the price gives the cost.
Typical uses
- Hot water cylinder or boiler: how much electricity does one fill need?
- Pool, bath or kettle: how long does heating take?
- Workpieces and metal parts: energy needed for preheating.
Frequently asked questions
How do you calculate heat energy?
With Q = c · m · ΔT, where c is the specific heat capacity, m the mass and ΔT the temperature difference in kelvin.
How much energy does it take to heat one litre of water by 1 °C?
About 4.18 kJ, roughly 0.00116 kWh. From 10 to 100 °C one litre needs a little over 0.1 kWh.
Why is the real energy higher?
Because no appliance turns all energy into useful heat and some is lost to the surroundings. Efficiency accounts for this.
Does the formula work for boiling or melting?
Only up to the boiling or melting point. At a phase change, latent heat of vaporisation or fusion is added.
Sources and legal basis
- Wikipedia – Spezifische Wärmekapazität: Q = c · m · ΔT and table values
- Wikipedia – Table of specific heat capacities (water 4.1813 kJ/(kg·K) at 25 °C, aluminium 0.897, iron 0.449, copper 0.385, air 1.0035)
- Wikipedia – Kilowattstunde (1 kWh = 3600 kJ)
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