Your water heater may be keeping you in more hot water than you're looking for when it comes to your gas or electric bill.
It's often hard to tell just how much it costs to heat your water because most utility bills don't split out the energy consumption of specific appliances. But, unless you've taken steps to keep it under control, it's a safe bet your household's water heating cost is sizable.
It takes a lot of energy to convert cold water to hot water--about 8.3 BTUs to raise one gallon of water 1 degree Fahrenheit. So, if water reaches your house at 60 degrees and your dishwasher requires 140-degree water, it takes 664 BTUs to heat each gallon of water, or about 10,000 BTUs to heat the 15 gallons of water per load used by the typical dishwasher. That represents 8 cents' worth of natural gas, at the national average price of 62 cents per therm, or 23 cents' worth of electricity at 8 cents per kilowatt-hour--if your heater's 100% efficient, which it isn't.
Even the best-insulated electric water heater leaks heat to its surroundings, typically to the tune of about $65 per year. A gas heater does even worse, losing about a fourth of its energy up the flue while it's heating water.
Saving energy on hot water calls for a two-pronged attack--use less heat and less hot water by lowering the temperature or reducing the number of gallons used. Of the two approaches, the first is easier, and can produce the greatest savings. You don't need a lot of new equipment to use less heat. Check your water heater's temperature setting. You could be throwing money away by running your dishwasher and washing machine at excessively high temperatures.
How hot should hot water be? A dishwasher is your most demanding user, and makers recommend 140 degrees for best results. There's no reason to keep your water thermostat higher than this, and you might try a lower setting to see if your dishes still get clean. Savings depend on utility rates, cold water supply temperature and heater setting.
Installing inexpensive flow restricters uses less water for showers and faucets. Also, make sure your hot water faucets don't leak. One drop a second dumps 400 gallons of expensive hot water a year.
Storage heat losses can be reduced about 15% by dropping the thermostat from 140 degrees to 130 degrees. Older water heaters can be helped by installing an insulation kit.
Turn off the water heater when you go on vacation. For less than 24 hours this doesn't pay off, but for longer periods, it makes a real difference.
Tankless, or instantaneous, water heaters eliminate storage losses except for warming delivery pipes each time they operate. They can maintain maximum output indefinitely, but there is no backlog of preheated water since there is no storage tank. Limited delivery rates, usually less than two gallons per minute, make water-saving faucets and shower heads more useful.
Heat-pump water heaters can be efficient but have high initial costs.