Your water heater is one of the more robust consumers of energy among your home appliances. In the average home, the hot water heater is responsible for about 17 percent of the total energy use, according to the Department of Energy. If you can calculate how much energy you expend heating water, however, you will be armed with the information you need to improve your efficiency and bring your bills down to a minimum.
Exactly how many watts an electric water heater uses depends on a number of variables, including the age and size of the unit, whether it is a tank or on-demand model, what temperature you set it to, how much hot water you use in a day, and other factors. You can come up with a cost estimate by multiplying the number of watts your heater uses by the price you pay per kWh by the number of hours the heater is active per day, then dividing by 1,000. Typically, a hot water heater that uses a tank will run for three to five hours per day. So, a 4,000-watt heater used for three hours a day at $.10 per kWh will cost $1.20 per day, about $36.50 per month, or $438 per year.
If you use a gas hot water heater, the same factors affect the cost as with their electric cousins. The formula for estimating your bill is similar as well: Multiply the therms your heater uses per hour times the number of hours it's on times the price you pay for therms. For example, if you pay $1 per therm and use a heater that consumes .205 therms per hour, for three hours per day,
your totals come to about $.62 per day, $18.70 per month and $224 per year.
Generally speaking, a gas water heater will cost less per month than an electric model, since natural gas prices tend to be lower than the cost of electricity. Going by the examples given above, where the electric heater costs $438 in fuel vs. $224 for gas, you would save $214 per year using gas, although the exact numbers you see would depend on all the other variables in play, such as the efficiency of your unit.
To refine your calculations, consider that how much gas a hot water heater uses depends on its Energy Factor, or EF rating. The higher the number the better, with the most efficient models weighing in around .67. If you need to purchase an electric water heater, look for models with EF ratings in the 90s. You can also look for models that use alternative methods of heating the water, such as solar heaters or heat pumps.
Tankless water heaters warm up water on demand, rather than storing a reservoir that is kept hot at all times. Generally speaking, these units will consume less energy than a traditional hot water heater, although how much electricity tankless water heaters use will still depend on the demand you create in your home. Since they don't need to heat water when you aren't using them, tankless heaters may only run for two hours a day or so.
According to the Department of Energy, tankless heaters are around 24 to 34 percent more efficient than heaters with tanks in homes that use 41 gallons or less of hot water per day, or 8 to 14 percent more efficient in homes that use 86 gallons of water or more. Keep in mind, however, these models also to cost more to purchase and may require new wiring in your house, which will offset some of your energy savings.
To reduce how much electricity or gas your hot water uses and bring your bills down, consider these tips: