OFFICE OF BUILDING TECHNOLOGY, STATE AND COMMUNITY PROGRAMSENERGY EFFICIENCY AND RENEWABLE ENERGY • U.S. DEPARTMENT OF ENERGY

Buildings forthe 21st CenturyBuildings that are moreenergy efficient, comfortable,and affordable...that’s thegoal of DOE’s Office of BuildingTechnology, State andCommunity Programs (BTS).To accelerate the developmentand wide application of energyefficiency measures, BTS:• Conducts R&D on

technologies and conceptsfor energy efficiency,working closely with thebuilding industry and withmanufacturers of materials,equipment, and appliances

• Promotes energy/money

saving opportunities to bothbuilders and buyers of homesand commercial buildings

• Works with state and local

regulatory groups to improvebuilding codes, appliancestandards, and guidelines forefficient energy use

• Provides support and grants

to states and communitiesfor deployment of energyefficient technologies andpractices

HEATINGDomestic water heating accounts for between15 and 25 percent of the energy consumed inhomes. Water-heating energy costs can bemanaged by selecting the appropriate fuel andwater heater type, using efficient systemdesign, and reducing hot water consumption.TYPES OF WATER HEATERSStorage-type water heaters, the primary focuswithin this fact sheet, are the most commondomestic hot water (DHW) heating systemselected today. However, other types of waterheaters may be very cost effective.Storage water heaters—heat and store waterin a tank ranging in size from 20 to 80 gallons.They offer a ready reservoir of hot water,although “standby” energy losses are higherthan with some other types. Conventional fuelsources include natural gas, electricity,propane, and fuel oil.Heat pump water heaters are electric storagewater heaters that are two to three times asefficient as conventional electric resistanceunits. Because they remove heat from thesurrounding air, they are most effective inwarm climates.Combination space and water heatingsystems—are storage water heating systemsproviding space heating plus DHW. Separatewater heaters and forced-air or hydronicsystems may be combined, or a single-sourcesystem may be purchased. Because heatingneeds of small, well-insulated homes often arelow, combination systems can be anexcellent choice.

heaters—heat water directly without use of astorage tank. Demand systems produce alimited amount of hot water—a 70°F watertemperature rise is possible at a flow rate offive gallons per minute through gas waterheaters and two gallons per minute throughelectric water heaters. These are best suitedfor low-demand or remote applications.Tankless coil water heaters—use a heatexchanger integrated with a space-heatingboiler to heat water instantaneously. These aregenerally recommended for use only in anextremely cold climate.An indirect water heater is a tankless coilwater heater with a separate storage tank toreduce boiler cycling. When matched with ahigh-efficiency boiler, this becomes a mostefficient hot water system.

Storage tank Heat pump

Drain valve

Thermostat

Accesscover

Heat

trap

Hot water out

Cold water in

Temp/pressure relief valve

Sacrificial annode rod

HEAT PUMP WATER HEATERHeat pump technology can provide costeffective water heating in mild climates.

ed, 

doo

ec

a

ca

oo

a

g

te exterior ventilation.

he conditioned space when a power

 system using a fan is incorporated to

ombustion gases through the flue,

a sealed combustion system

ely ducts in outside air for combustion

cts out combustion gas exhaust.

ATION AND MAINTENANCE

et the minimum applicable

, plumbing, electrical, and/or other

ements when installing a water

tem. Initial installation

nts include installing a second anode

nation anode/hot outlet nipple) and

t drain valve (full-port 3⁄4-inch

rass ball valve with hose adapter).

er placement can impact operating

ially if the unit is poorly insulated.

ment to facilitate short, insulated

 to bathrooms and kitchens is most

o improve energy efficiency,

e water heaters are best located in

d space, except in extremely hot

here tank heat loss increases the

d.

ater heater maintenance can

y extend water heater life and

ss of efficiency over time. Routine

ce involves flushing a quart of water

orage tank every three months,

e temperature and pressure relief

 six months, and inspecting the

every three to four years.
per gallon (prices often vary seasonally).

Heat trap

Electric Gas

Cut-out for combustion air

Cut-outs for heating coil elements

Hot water tank

Heat exchanger Hot water

Cold water inDrain water

Preheated cold water to plumbing fixtures and to water heater

Faucet

DRAINWATER HEAT RECOVERYThis system captures waste heat through heat exchangefrom the wastewater drains.

capacity. Benefits ultimately depend on many variables including installation, fuel type, system geometry, exchangercharacteristics, and usage patterns.Flue dampers seal off the flues of naturally drafted gas waterheaters when there is no exhaust to reduce heat loss up the flue.Timers can shut off electric water heaters for a set time period,such as when time-of-use electric rates are highest or whenoccupants normally do not use hot water. Depending on shutofftime, setpoint, and tank insulation level, timers may or may not becost-effective. In addition, they may be inconvenient when muchhot water is needed while the water heater is turned off.Load management devices enable utilities to turn off electricwater heaters remotely during periods of heavy electricaldemand. Allowing this option to be installed, where available,typically results in a monthly credit from the utility.

IMPROVING WATER HEATER EFFICIENCYWith any DHW system, methods for reducing hot water coststart with lowering the thermostat. Set the thermostat lowenough to minimize safety concerns (scalding) yet high enoughfor washing (dishes, clothes) and bathing. A setting of 120°F

generally meets most household needs.Installing water heater insulating “jackets” of R-11 or higher canbe cost effective in reducing standby losses on storage-type units,especially older or poorly insulated ones. Greater benefit isachieved when the hot water tank is installed outside of conditioned space (e.g., garage). For safety, however, never block anycontrols, valves, or airways for combustion or exhaust.Pipe insulation is inexpensive and easy to install. Add it to hotand cold water pipes in unconditioned spaces such as garages,attics, and crawlspaces and for a distance of at least six feetfrom the tank.Heat traps prevent heated water in a storage tank from mixingwith cooled water in pipes, a process called thermosiphoning.Some new water heaters have built-in heat traps, although theycan be added to new or existing water heaters. Flexibleconnectors with a loop in the vertical line offer an effective,

al.

ater

age

Times

used in

hour

Gal. used

in hour

x =

x =

x = 

x =

x = 

x =

x =

x =

x =

) 

sed in hour =

f hot water usage might entail:

x 2= 03

x 2 = 8

x 1= 2 

x 2 = 4

x 1= 5 

) 

sed in hour = 94

rers Association

er conservation measures.
per gallon (prices often vary seasonally).

Heat trap

Electric Gas

Cut-out for combustion air

Cut-outs for heating coil elements

Hot water tank

Heat exchanger Hot water

Cold water inDrain water

Preheated cold water to plumbing fixtures and to water heater

Faucet

DRAINWATER HEAT RECOVERYThis system captures waste heat through heat exchangefrom the wastewater drains.

capacity. Benefits ultimately depend on many variables including installation, fuel type, system geometry, exchangercharacteristics, and usage patterns.Flue dampers seal off the flues of naturally drafted gas waterheaters when there is no exhaust to reduce heat loss up the flue.Timers can shut off electric water heaters for a set time period,such as when time-of-use electric rates are highest or whenoccupants normally do not use hot water. Depending on shutofftime, setpoint, and tank insulation level, timers may or may not becost-effective. In addition, they may be inconvenient when muchhot water is needed while the water heater is turned off.Load management devices enable utilities to turn off electricwater heaters remotely during periods of heavy electricaldemand. Allowing this option to be installed, where available,typically results in a monthly credit from the utility.

IMPROVING WATER HEATER EFFICIENCYWith any DHW system, methods for reducing hot water coststart with lowering the thermostat. Set the thermostat lowenough to minimize safety concerns (scalding) yet high enoughfor washing (dishes, clothes) and bathing. A setting of 120°F

generally meets most household needs.Installing water heater insulating “jackets” of R-11 or higher canbe cost effective in reducing standby losses on storage-type units,especially older or poorly insulated ones. Greater benefit isachieved when the hot water tank is installed outside of conditioned space (e.g., garage). For safety, however, never block anycontrols, valves, or airways for combustion or exhaust.Pipe insulation is inexpensive and easy to install. Add it to hotand cold water pipes in unconditioned spaces such as garages,attics, and crawlspaces and for a distance of at least six feetfrom the tank.Heat traps prevent heated water in a storage tank from mixingwith cooled water in pipes, a process called thermosiphoning.Some new water heaters have built-in heat traps, although theycan be added to new or existing water heaters. Flexibleconnectors with a loop in the vertical line offer an effective,

al.

ater

age

Times

used in

hour

Gal. used

in hour

x =

x =

x = 

x =

x = 

x =

x =

x =

x =

) 

sed in hour =

f hot water usage might entail:

x 2= 03

x 2 = 8

x 1= 2 

x 2 = 4

x 1= 5 

) 

sed in hour = 94

rers Association

er conservation measures.
OFFICE OF BUILDING TECHNOLOGY, STATE AND COMMUNITY PROGRAMSENERGY EFFICIENCY AND RENEWABLE ENERGY • U.S. DEPARTMENT OF ENERGY

Buildings forthe 21st CenturyBuildings that are moreenergy efficient, comfortable,and affordable...that’s thegoal of DOE’s Office of BuildingTechnology, State andCommunity Programs (BTS).To accelerate the developmentand wide application of energyefficiency measures, BTS:• Conducts R&D on

technologies and conceptsfor energy efficiency,working closely with thebuilding industry and withmanufacturers of materials,equipment, and appliances

• Promotes energy/money

saving opportunities to bothbuilders and buyers of homesand commercial buildings

• Works with state and local

regulatory groups to improvebuilding codes, appliancestandards, and guidelines forefficient energy use

• Provides support and grants

to states and communitiesfor deployment of energyefficient technologies andpractices

HEATINGDomestic water heating accounts for between15 and 25 percent of the energy consumed inhomes. Water-heating energy costs can bemanaged by selecting the appropriate fuel andwater heater type, using efficient systemdesign, and reducing hot water consumption.TYPES OF WATER HEATERSStorage-type water heaters, the primary focuswithin this fact sheet, are the most commondomestic hot water (DHW) heating systemselected today. However, other types of waterheaters may be very cost effective.Storage water heaters—heat and store waterin a tank ranging in size from 20 to 80 gallons.They offer a ready reservoir of hot water,although “standby” energy losses are higherthan with some other types. Conventional fuelsources include natural gas, electricity,propane, and fuel oil.Heat pump water heaters are electric storagewater heaters that are two to three times asefficient as conventional electric resistanceunits. Because they remove heat from thesurrounding air, they are most effective inwarm climates.Combination space and water heatingsystems—are storage water heating systemsproviding space heating plus DHW. Separatewater heaters and forced-air or hydronicsystems may be combined, or a single-sourcesystem may be purchased. Because heatingneeds of small, well-insulated homes often arelow, combination systems can be anexcellent choice.

heaters—heat water directly without use of astorage tank. Demand systems produce alimited amount of hot water—a 70°F watertemperature rise is possible at a flow rate offive gallons per minute through gas waterheaters and two gallons per minute throughelectric water heaters. These are best suitedfor low-demand or remote applications.Tankless coil water heaters—use a heatexchanger integrated with a space-heatingboiler to heat water instantaneously. These aregenerally recommended for use only in anextremely cold climate.An indirect water heater is a tankless coilwater heater with a separate storage tank toreduce boiler cycling. When matched with ahigh-efficiency boiler, this becomes a mostefficient hot water system.

Storage tank Heat pump

Drain valve

Thermostat

Accesscover

Heat

trap

Hot water out

Cold water in

Temp/pressure relief valve

Sacrificial annode rod

HEAT PUMP WATER HEATERHeat pump technology can provide costeffective water heating in mild climates.

ed, 

doo

ec

a

ca

oo

a

g

te exterior ventilation.

he conditioned space when a power

 system using a fan is incorporated to

ombustion gases through the flue,

a sealed combustion system

ely ducts in outside air for combustion

cts out combustion gas exhaust.

ATION AND MAINTENANCE

et the minimum applicable

, plumbing, electrical, and/or other

ements when installing a water

tem. Initial installation

nts include installing a second anode

nation anode/hot outlet nipple) and

t drain valve (full-port 3⁄4-inch

rass ball valve with hose adapter).

er placement can impact operating

ially if the unit is poorly insulated.

ment to facilitate short, insulated

 to bathrooms and kitchens is most

o improve energy efficiency,

e water heaters are best located in

d space, except in extremely hot

here tank heat loss increases the

d.

ater heater maintenance can

y extend water heater life and

ss of efficiency over time. Routine

ce involves flushing a quart of water

orage tank every three months,

e temperature and pressure relief

 six months, and inspecting the

every three to four years.