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Before you buy...
Water Heating
Related Product Advice
Water heating can use 15-20% of the home’s total energy use, making it the second largest energy consumer in the home. So when making a water heating choice, consider the part that a water heater selection plays in the overall energy budget. Selecting a high efficiency unit can pay for itself quickly. Modifying some simple behaviors can shorten the payback period even more.
Even though a high efficiency unit usually costs more upfront, by estimating the potential savings over the expected life of the unit, the additional price can be considered an investment. Frequently a more efficient water heater will cost between 15-25% more to purchase, but cost 50% less to operate. Using this formula, the initial cost could be reclaimed in the first years of operation. Compare the unit’s EnergyGuide label for estimated energy costs.
Water heater efficiency is measured using an Energy Factor (EF) rating. The EF rates the overall efficiency of the water heater for gas, oil, or electric powered units including standby heat loss. In all cases, a higher EF indicates a higher efficiency with a maximum value of 2.0.
Reduce standby losses in hot water generation by wrapping storage tanks with R-16 insulation jackets. Be careful not to cover the relief or drain valve or the air inlet to the burner (gas heaters only). Water heater jackets and insulation are inexpensive, easy to install, and readily available. Heat traps, anti-convection valves, and pipe insulation also reduce heat losses. Indirect-fired water heaters heat the water indirectly by attaching a heat exchanger and a water storage tank to a central space-heating boiler. Hot water from the boiler is circulated through the heat exchanger in a storage tank. The EF for the water heating depends on the efficiency of the boiler and the tank insulation. With a high-efficiency boiler, and a well insulated tank, the EF can be over 0.80. A few high-efficiency, gas-fired, combination water/space heaters are commercially available. These provide hot water and heat the house. The EF for water heating with these units can be higher than 0.86.
Instantaneous or “demand” water heaters eliminate the storage tank and therefore the energy losses associated with it. Water is only heated when the occupant “demands” hot water by opening the hot water faucet. The hot water flow-rate is limited by the design of the specific instantaneous water heater chosen. Gas-fired instantaneous water heaters have an EF of about 0.75. Electric instantaneous water heaters have an EF of 1.0.
Reduced piping losses: Insulate hot water pipes from the heater to their end use with R-6 insulation. If this level of insulation is not possible, be sure to insulate all hot water pipes in unconditioned space and the first four feet of hot water pipes extending out of the water heater. This can account for more than 30% of hot water heating energy input, by optimizing the hot water system design (minimize end-use-to-tank distances), insulating pipes and wrapping the storage tank. Reduce construction costs and piping losses by locating the water heater in close proximity to showers, the washing machine and the kitchen.
Reduce hot water temperatures to provide the minimum acceptable temperature for intended use. Set water heater temperature to 120 degrees. Higher temperatures lead to scalding and more standby losses, lower temperatures can lead to Legionella bacteria forming in the water tank. If higher temperatures are desired for dish washing, use dishwashers with booster heaters.
How Much Can You Save?
Set Back in Degrees Dollars Per Month
150 to 120 1.80
150 to 130 1.20
150 to 140 0.60
Reduced end use: Select low-flow shower heads and water-efficient appliances to reduce demand for hot water within the home. Low-flow showerheads use less than half the water of conventional ones. Showers alone account for 40% of a home’s hot water use on average, and low-flow shower heads are an inexpensive solution.
Once the specifics of hot water usage are understood, the system that best suits the situation can be determined. In some environments and climates, active solar hot water heating can provide most if not all of the water heating needs for a home. In other environments and climates active solar in combination with a small tankless hot water heater could be an energy efficient system.
The water heating options are numerous and directly linked to need. Make inquiries in the local area to determine what system or combination of systems are most efficient and most effective.
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