Reviewed October 1993
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Hot water is as close as the faucet in the kitchen, bathroom(s) and laundry areas of most American homes. Hot water is taken for granted and looked upon as an integral part of the household. Little thought is given to the cost of heating water because its use is constant rather than seasonal, as with a central heating system.
The heating of water accounts for 15 percent of your total energy bill. If your utility bills ran $1,000 last year, that means you spent approximately $150 to heat water for your home. You can't do without hot water, but there are several ways to conserve it so that energy requirements and costs will be less.
Residential water heating is accomplished with gas, electric or oil-fired units. Gas and electric units are usually the automatic storage type, with the heater, storage tank, insulation and controls all combined in a single unit. Oil-burning units commonly use a direct-fired water heater with pipe coils in the boiler. Such units may or may not be combined with a hot water storage tank.
Hot water use depends on the number of people in a household, the number of bathrooms and whether there is a clothes washer (or) automatic dishwasher.
Water heating units are specified in terms of tank size, rate of heat input, maximum estimated hot water usage per hour and recovery or reheating capacity rated in gallons per hour. An oversized unit uses energy to keep unneeded water hot; an undersized unit cannot supply a sufficient amount of hot water.
The American Gas Association recommends a 30-gallon (115-liter) water heater for a family of two with one bathroom and an automatic clothes washer. For each additional person in the family and for each additional bathroom in the household, 3.5 gallons (13 liters) should be added to the tank capacity. If a dishwasher is used, the tank capacity should be increased by five gallons (19 liters). A reliable heating and plumbing contractor can best determine the size tank needed in your household.
If you must replace a water heater, make energy efficiency your main criterion. Look for information indicating how efficiently the unit uses the energy required for operating it. Also look for a thickly insulated outer shell. When replacing a gas-fired unit, select one equipped with a low-consumption pilot that is matched to the rate of heat loss of the heater.
Relocate the unit, if necessary, as close as possible to areas of major hot water use. Use small-diameter pipes for hot water supply lines to minimize heat loss and to reduce the volume of trapped water. The design of some homes may make it more economical to have two small units rather than one large unit that is not located close to any water-using equipment.
A thermostat setting of 110 degrees Fahrenheit to 120 degrees Fahrenheit (43 degrees to 49 degrees Celsius) on a water heater is sufficient if you do not have an automatic dishwasher; a setting of 140 degrees Fahrenheit (60 degrees Celsius) is recommended if you do have one. Temperatures over 140 degrees Fahrenheit (60 degrees Celsius) shorten the life of a glass-lined tank.
If any hot water pipes have to run more than 70 feet (21 meters), consider installing a separate 20-gallon (75-liter) unit near the main bathroom; set the thermostat at 110 degrees Fahrenheit (43 degrees Celsius). Or locate a separate 20-gallon (75-liter) water heater near the dishwasher and set the thermostat at 140 degrees Fahrenheit (60 degrees Celsius) Over the life of a water heater, either will pay for itself in energy saved.
Twice a year (monthly if you live in an area with heavy mineral deposits in the water) empty a bucket of water from your hot water storage unit. The drain cock is located near the bottom of the tank. This will help remove sediment which insulates the tank from the source of heat and wastes energy.
Heat losses from a hot water storage tank and supply lines can be significant. Examine your storage tank carefully; touch the surface. If it's hot, or even warm, some of the energy used to heat the water is being wasted. You can remedy this by wrapping unfaced batt or blanket insulation around and over the shell of the tank. It is estimated that 2 inches of insulation will save about $25 a year on an 80-gallon tank, and with four inches, more than $30. Figure a $15 to $20 annual savings if you put two to three inches of insulation around a 40-gallon tank.
Pipe insulation is needed especially where pipes run through unheated areas such as basements or crawl spaces. Several types of insulation for wrapping or covering pipes are available at hardware or building supply stores. Insulate cold-water pipes to reduce the chance of winter freeze-up.
Electric heat tapes may be necessary in cases where pipes are exposed to extreme cold. Heat tape must be installed carefully. A tape should never overlap itself, or it will short out and could result in a fire. The tape should be spirally wrapped around a water pipe and secured in position with duct tape. Finally, the pipe and tape should be covered with insulation.
A leaking hot-water faucet is an energy waster and should be repaired immediately. The replacement of washers is a simple operation described in every basic homeowner's maintenance guide. A faucet that leaks one drip per second wastes 2,400 gallons (9,120 liters) of hot water each year. That's enough to run 160 full cycles on an automatic dishwasher!
GH5995, reviewed October 1993