Calculate the kWh of energy, heater kW or heating time needed to heat water from a starting to a target temperature, in litres or gallons.
kW to Heat Water Formula
The following ideal formula assumes liquid water at 1 kg/L and an approximate constant specific heat. It gives useful heating power with no losses; divide by the overall efficiency fraction to estimate heater input power. The model excludes freezing, boiling, evaporation and heating the container.
Variables:
- P is the power required (kW)
- V is the volume of water (liters)
- ฮT is the temperature rise (ยฐC)
- C is an approximate specific heat capacity of water (4.186 kJ/kgยทยฐC); it varies with temperature
- t is the time (hours)
To calculate the power required to heat water, multiply the volume of water by the temperature rise and the specific heat capacity of water, then divide by the product of time in seconds (time in hours multiplied by 3600).
| Volume (L) | Temperature Rise (ยฐC) | Time (min) | Power (kW) | Power (W) | Power (MJ/h) |
|---|---|---|---|---|---|
| 1 | 80 | 3 | 1.860 | 1,860 | 6.698 |
| 2 | 80 | 4 | 2.791 | 2,791 | 10.046 |
| 5 | 40 | 5 | 2.791 | 2,791 | 10.046 |
| 10 | 30 | 10 | 2.093 | 2,093 | 7.535 |
| 10 | 20 | 10 | 1.395 | 1,395 | 5.023 |
| 20 | 30 | 15 | 2.791 | 2,791 | 10.046 |
| 30 | 25 | 20 | 2.616 | 2,616 | 9.418 |
| 40 | 20 | 10 | 5.581 | 5,581 | 20.093 |
| 50 | 35 | 30 | 4.070 | 4,070 | 14.651 |
| 50 | 40 | 30 | 4.651 | 4,651 | 16.744 |
| 60 | 30 | 30 | 4.186 | 4,186 | 15.070 |
| 75 | 45 | 45 | 5.232 | 5,233 | 18.837 |
| 80 | 35 | 60 | 3.256 | 3,256 | 11.721 |
| 100 | 30 | 60 | 3.488 | 3,488 | 12.558 |
| 100 | 50 | 60 | 5.814 | 5,814 | 20.930 |
| 120 | 25 | 30 | 6.977 | 6,977 | 25.116 |
| 150 | 40 | 60 | 6.977 | 6,977 | 25.116 |
| 180 | 35 | 90 | 4.884 | 4,884 | 17.581 |
| 200 | 30 | 60 | 6.977 | 6,977 | 25.116 |
| 300 | 50 | 180 | 5.814 | 5,814 | 20.930 |
| * Rounded to 3 decimals (W rounded to the nearest unit). Assumes water density 1 kg/L and specific heat c = 4.186 kJ/kgยทยฐC. Formula: P(kW) = V(L) ร ฮT(ยฐC) ร 4.186 รท time(s). Unit links: 1 kW = 1000 W, 1 kW = 3.6 MJ/h. | |||||
What is kW to Heat Water?
kW to heat water is a measure of the energy rate required to raise the temperature of a given volume of water by a certain degree over a specified period. It is an important calculation in designing heating systems, such as water heaters and boilers, to ensure they have sufficient power to meet the heating demands.
How to Calculate kW to Heat Water?
The following steps outline how to calculate the power required to heat water.
- First, determine the volume of water to be heated (V) in liters.
- Next, determine the desired temperature rise (ฮT) in degrees Celsius.
- Next, determine the time over which the temperature rise should occur (t) in hours.
- Next, gather the formula from above = P = (V * ฮT * C) / (t * 3600).
- Finally, calculate the power required (P) in kilowatts.
- After inserting the variables and calculating the result, check your answer with the calculator above.
Example Problem :
Use the following variables as an example problem to test your knowledge.
Volume of water (V) = 100 liters
Temperature rise (ฮT) = 30ยฐC
Time (t) = 2 hours
