Enter the mass of the water (kg), the change in temperature (T), and the total energy input into the water heater (J) into the calculator to determine the Water Heater Efficiency. 

Water Heater Efficiency Formula

The following formula is used to calculate the Water Heater Efficiency.

Ewh = m*C*dT / Q * 100
  • Where Ewh is the Water Heater Efficiency (%)
  • m is the mass of the water (kg) 
  • C is the change in temperature (C) 
  • Q is the total energy input into water heater (J) 
  • C is the specific heat of water (4.186 J /kg-C)

To calculate the water heater efficiency, multiply the mass, specific heat, and change in temperature together, then divide by the total energy input into the water heat.

How to Calculate Water Heater Efficiency?

The following example problems outline how to calculate the Water Heater Efficiency.

Example Problem #1

  1. First, determine the mass of the water (kg). In this example, the mass of the water (kg) is given as 16 .
  2. Next, determine the change in temperature (C). For this problem, the change in temperature (C) is given as 20 .
  3. Next, determine the total energy input into water heater (J). In this case, the total energy input into water heater (J) is found to be 2200.
  4. Finally, calculate the Water Heater Efficiency using the formula above: 

Ewh = m*C*dT / Q * 100

Inserting the values from above and solving yields: 

Ewh = 16*4.186*20 / 2200 * 100 = 60.88 (%)

Example Problem #2

Using the same method as above, determine the variables required by the equation. For this example problem, these are provided as:

mass of the water (kg) = 24

change in temperature (C) = 30

total energy input into water heater (J) = 5000

Enter these given values yields: 

Ewh = 24*4.186*30 / 5000 * 100 = 60.278 (%)