Consider each type of hot water heater for a home
ProudGreenHome: What is the most efficient hot water heater for residential use?
Melissa Rappaport Schifman:As with most questions that deal with tradeoffs, the answer to this question will always begin: it depends. On what? Budget, type of home and hot water usage, and fuel sources available. Having said that, as a homeowner who looked into each of the following as potential options, here is my opinion.
On-Demand:A lot of people really like the instant on-demand tankless hot water heaters. The efficiency there is gained by only using energy when you need hot water. But these systems might not work that well when there are several people in a household that may want to shower at the same time. They also require venting, which may not be practical for some homes. For vacation homes or homes that are frequently vacant, I would highly recommend the on-demand water heaters. For homes with a lot of hot water usage, I think the results are mixed.
Solar: Another extremely efficient water heater uses solar thermal collectors — so the water is heated by free energy from the sun. The drawbacks are the upfront investment (household systems can cost in the range of $7,000-$10,000) and the need for space for an additional hot water tank — usually a 50-70 gallon tank. The initial cost, however, will be paid back — typically within 5 to 7 years — by lower operating costs.
Geothermal: In our case, we have a geothermal heat pump to heat and cool our home, and we have what's called a "desuper heater" — an auxiliary tank where the excess heat is dumped whenever the pump is running. It is basically a pre-heat tank, so in the summer and winter months, our water is already heated for us. The only time the back-up gas boiler kicks in is during the spring and fall months when we are not heating or cooling our house. If it is within your budget to get a whole-house geothermal system, then I think this is the most efficient option.
In any case, there are many easy things to do to make a hot water heater more efficient without a lot of investment. If you have a tank, one of the most important things to do is to properly insulate the tank (and pipes) so that minimal heat is lost during storage. Also, if you are leaving town, you can turn it off entirely so that energy is not wasted keeping the water hot while you are gone. Finally, turning the temperature down a few degrees will also save energy, because you usually mix it with some cool water anyway to get it to the right temperature. How often is scalding hot water required for the shower or washing machine?
See the features section on ProudGreenHome for more information on hot water heaters.
Topics: Going Green
Melissa Rappaport Schifman Melissa provides sustainability consulting services for businesses in the Twin Cities metropolitan area. Melissa is also the founder of Green Intention LLC, where she writes and blogs about her experience in getting her own home LEED Gold certified--and then trying to live more sustainably in the home. She chairs her congregations Task Force for Sustainability, has her MBA, Master's in Public Policy, and is a LEED AP for Homes. www