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How much are you paying for hot water? If your water use is comparable to typical households, 25% of your energy bill goes to water heating.
A home's hot water system includes the water heater as well as the pipes used to deliver the water. The ultimate gauge of a well-designed system is the speed of hot water delivery and energy efficiency of the entire system. An efficient system will not waste more than two to four cups of water at the fixture while you're waiting for hot water to arrive.
If you're watching gallons go down the drain every time you take a shower, it may be time for some improvements.
Insulation for older water heaters
A storage water heater holds hot water in a tank so that it's always ready when you need it. This is the most common type of water heater in the United States. Older storage water heaters do not have as much internal insulation as newer models sold in California. Poorly insulated water heaters experience what's known as standby loss. Heat is slowly but continually lost through the tank's surfaces; the water heater has to use extra energy to compensate for this loss and keep the water in the tank at a set temperature.
To reduce the standby energy loss of older water heaters, install jacket insulation—an inexpensive product available at most home improvement stores. Jacket insulation wraps around the tank and reduces the heat loss of older water heaters by about 10% or more. For new water heaters, make sure that installing jacket insulation will not void the warranty.
Pipe insulation
Plumbing pipes may not be easily accessible in all homes, but if they are, an effective way to reduce energy loss is to insulate the entire length of hot water pipe from the water heater to the kitchen. An even better option is to insulate all accessible hot water pipes in the home. If hot water pipes run through the attic, a low-cost option is to bury them in ceiling insulation.
Pipe insulation keeps water in the pipes warm longer, reducing the energy used to heat water and reducing the amount of water wasted down the drain while waiting for hot water to arrive.
High-efficiency water heater
There are five basic options for water heating:
- Storage water heater, which stores hot water in a large tank until you need it
- Tankless water heater (also called flash or on-demand heater), which heats water instantly when you need it rather than storing hot water
- Heat-pump water heater, a more energy-efficient alternative to an electric storage heater
- Combination water/space heating system, which can heat your home as well as your water
- Solar water heater, used in combination with a backup gas or electric water heater (see our GreenPointer on Renewable Energy)
Water heaters may be fueled by either natural gas or electricity. Gas water heating is significantly less expensive than electric water heating.
Homes with Gas Service
If your home has gas service, choose a gas-fired storage or tankless water heater with an Energy Factor (EF) of 0.67 or greater. EF is the ratio of energy output to energy consumption of a water heater in a typical day. A tankless water heater requires much less space and is typically more energy efficient than a storage water heater. However, tankless water heaters typically cost more to purchase and install than storage water heaters.
Homes without Gas Service
An electric storage water heater is typically the most expensive water heating option. A tankless electric water heater typically uses more electricity than an electric storage water heater. If switching from electric to gas water heating is not an option, consider replacing the electric storage water heater with an efficient heat-pump water heater. Heat pumps are about three times as efficient as the most efficient electric water heaters.
Tankless Water Heater
If choosing a tankless water heater, choose gas over electric and install it as close as possible to the points where hot water is used. The unit should have a variable-set thermostat and an electronic ignition, and be appropriately sized. Gas tankless water heaters typically have more capacity than electric tankless heaters; however, that extra capacity to supply hot water may tempt some people to take longer showers, which would reduce their energy savings.
Combined Space and Water Heating
Look for ways to save energy and get the most out of equipment by combining water heating and space heating. These systems include boilers or water heaters that serve a home's heating system as well as providing domestic water.
For more information about water heating options, visit www.consumerenergycenter.org.
On-demand hot water circulation pump
Larger houses may require hot water circulation systems to reduce waiting time. However, conventional circulation systems with continuous or timed pump operation waste too much energy. A better option is an on-demand circulation pump.
These systems consist of a pump with on-demand controls (push button or motion-sensor activated) that circulate water from the existing hot water line through the cold line or via a dedicated return loop to the water heater. Only one pump is needed to supply hot water to all fixtures in the same loop. All pipes carrying circulated hot water must also be insulated. On-demand hot water circulation works for all systems: tank or tankless water heaters, and copper or PEX pipe.
Efficient plumbing system layout
Much of the energy used to heat water in homes is lost in long piping runs to sinks, showers and tubs located far from the water heater. Locating the water heater closer to the points where we actually use water reduces heat loss, gets hot water to the faucet or shower faster, and most importantly, reduces water wasted down the drain while waiting for hot water to come out of the tap.
To reduce the amount of water wasted while waiting for hot water to arrive at a fixture, pay attention to hot water pipe layout and pipe diameter. Design the layout so that it has the shortest runs possible, and use the smallest diameter possible for the appropriate fixture flow rate. The system should be designed so that no more than two to four cups of water would be wasted by a person waiting for hot water at a shower or faucet.
The most effective means of reducing energy and water loss is to locate the water heater close to all hot water fixtures, including bathrooms, the kitchen and laundry. A simple guideline is to keep the water heater within 12 feet of all fixtures. Measure this distance in floor plan view (aerial view), not the actual run of the pipes. (For example, if you are measuring the distance from a first-floor water heater to a second-floor shower, you would not include the vertical distance of the piping from the first floor to the second).
If you are not planning a major remodel of your home, you may not be able to change the water heater location. When building a new home or undertaking a major remodel, try to stack or cluster rooms that need water, and create a central core mechanical space for housing the water heater and pipes and integrating the furnace, air conditioner and ductwork.
More water heating tips
- Trap it. Consider installing heat traps on your storage water heater. Also known as back flow preventers, heat traps reduce convection heat loss by preventing hot water from circulating in the hot water pipes above the tank. Heat traps are installed in pairs at the tank: one on the hot water side and one on the cold water side. The traps are inexpensive, but require professional installation.
- Maintain it. One of the most important aspects of water heater maintenance involves checking, and occasionally replacing, a storage water heater's sacrificial anode. This metal rod keeps your water heater's inside elements from corroding. It should be removed from the water heater's tank every few years for inspection and replaced when more than six inches of core wire is exposed at either end of the rod. This can be done by a plumber or handy homeowner. Refer to your water heater's maintenance manual for the sacrificial anode location, and make certain the cold water supply is turned off before removing it. Information on water heater maintenance can be found at www.waterheaterrescue.com.