🚿 Water Heater Running Cost Calculator

Enter your electric water heater's wattage and estimated daily active heating time to calculate its running cost.

What the tool computes

An electric element only costs money while it is actually heating, so the sum runs on active hours rather than the hours the tank is switched on:

kWh per day  = watts / 1000 x active hours
monthly cost = kWh per day x 30 x rate
yearly cost  = kWh per day x 365 x rate

A 4,500 W element heating for 3 hours a day uses 13.5 kWh, which at $0.15 a kWh is $60.75 a month and $739.13 a year. That is a busy household; one or two people are usually nearer 1.5 hours. Put your own rate in the box before reading the total - at 30 cents the same tank costs $1,478 a year, and water heating is large enough that the difference is worth several hundred dollars.

Turning hot water into hours

The active-hours input is the one people guess at. Work it out from how much hot water you draw instead, using 8.34 lb per gallon and 3,412 BTU per kWh:

kWh  = gallons x 8.34 x temperature rise (F) / 3412
hours = kWh / (watts / 1000)

50 gallons a day lifted from 55F to 125F is a 70 degree rise: 50 x 8.34 x 70 / 3412 = 8.6 kWh, which is 1.9 hours on a 4,500 W element. Add ten per cent or so for the heat the tank loses standing there overnight.

This prices electric tanks only. A gas heater is billed in therms, and a heat pump water heater moves heat rather than making it, doing the same job for roughly a third of the kilowatt-hours.

Frequently asked questions

How much does an electric water heater cost to run per month?

Around $61 at 15 cents a kWh for a heavily used 4,500 W tank running three hours a day. A smaller household using half that comes in near $30.

How many hours a day does a water heater element actually run?

Typically one and a half to three, in short bursts after each draw. If you enter 24 you are pricing the element as though it never switches off, which overstates the bill by a factor of ten.

Does turning the tank thermostat down save money?

Some, and 120F is the usual recommendation. The saving is roughly 3 to 5% per 10 degrees, and it comes mostly from slower standby losses rather than from the showers, since you mix in less cold water to compensate.