Fact Sheet»

Description

This section covers hot water heaters, also referred to as domestic hot water systems (DHW). According to the U.S. Department of Energy 14% of the total energy consumed by an average home is used by hot water heating. The primary issues with hot water heaters are durability and energy consumption. The following comparative analysis identifies the relative economic, energy, and environmental implications of three options: conventional water heater, on-demand tankless water heater, and solar water heating.

Recommendations

Tankless water heaters are recommended as a balance of affordability, durability, and energy consumption. The consideration of first as well as operational cost is critical. The system has the added benefit of being wall mounted and compact, and therefore takes up less space than a traditional tank unit in a smaller home.

Solar is an economically viable option if utility service is limited to electricity and an electric water heater is the only option. It is the clear environmental winner across all types.

Install the highest available efficiency of gas water heater if a conventional system is used. The premium cost of the unit will be recouped over the life of the unit.

Water Heater Alternatives

Criteria Summaries

Cost: Conventional tank electric water heaters have the lowest first cost, but have a significantly higher operating cost. Conventional tank natural gas heaters are more expensive than electric tank models. Cost varies for all tank models with efficiency and durability, generally the more efficient the model the longer the warranty. Warranties are in 6, 9, and 12 year terms. Tankless systems are two to three times more expensive than storage tank models. Cost is associated with flow rate which is the number of gallons per minute (gpm) a unit can produce. A flow rate of 3 gpm has the rough service equivalent of a 40 gallon tank. Solar water heaters have the highest initial cost; in effect installing a solar system is paying for the hot water up front.

Energy: Solar water heaters are the best energy performers. Under ideal conditions they require little additional energy if properly installed and maintained. At a minimum they should produce 70% of hot water needs. Tankless water heaters, due to elimination of storage energy losses, use less energy than conventional storage tank water heaters. A gas tankless system will pay for itself in energy cost savings over a conventional gas unit. The premium cost of a high efficiency gas tank unit will be recouped over its lifetime as well. Electric water heaters are less efficient than gas water heaters if electricity generation and transmission losses are included. The annual cost of an electric hot water heater is triple that of natural gas tank systems. Energy Star does not currently rate water heaters.

IAQ: Natural gas combustion devices require proper venting to prevent potential backdrafting, which may cause carbon monoxide or carbon dioxide building up in the house. This problem is extended to solar systems if the back-up heating element if fueled by natural gas. Electric water heaters have no impact on indoor air quality, since they produce no emissions at the site of the water heater.

Expected Product Life: Tankless water heaters have the longest life expectancy of 20-30 years; that is twice the useful life compared to a tank water heaters. Tankless systems can be serviced and parts replaced helping to extend its useful term. Conventional tank water heaters have a life expectancy of approximately 10-15 years depending on quality. Failure of tank systems typically results from tank rust through, which cannot be repaired. The useful life of a solar water heating systems varies from 15-40 years. Like the tankless systems, components can be replaced or repaired with the exception of the storage tank which is subject to the risk of rust through.

Practice: Storage tank systems are standard practice. Tankless systems require some additional training. Solar water heating systems are still an emerging technology and a specialized professional installation is recommended.