The average American shower uses 12 gallons of heated water, the average tub bath only nine, though the bath may use more water over all.
Smaller tanks heating water closer to the rooms where it will be used are changing standards for household plumbing and lowering the energy spent to keep water hot for hours when none is needed. The U.S. Department of Energy's Energy Savers website recommends considering what fuel you'll use, energy efficiency and actual operating costs, as well as size, when considering which 20-gallon water heaters may best meet your family's needs. Does this Spark an idea?
Instructions
1. Determine which fuel you will use. Availability will be the first consideration. If you have natural-gas or propane service, it may reach only the lower floors of your house. To get the benefits of heating your water where it's used, you'll want to have at least one tank to serve the upstairs bathroom(s), and this may dictate using an electric heater, at least for that application. You might also be able to use passive or active solar-heating systems; most of these, except in very sunny and warm climates and unshaded settings, will heat the water you use indirectly, by running the sun-warmed water through a closed coil within the storage tank.
2. Learn the energy factor (EF) rating for each system you're considering. This measure of energy efficiency is calculated from the amount of energy transferred into the water as heat for each standardized unit of fuel burned over a typical day. The figures are usually stated in system manufacturers' literature; the higher the figure, the more efficient the system. Solar-powered heaters are rated for solar energy factor (SEF) and solar fraction (SF); though the solar heating itself burns no energy, many solar water heaters must rely on backup from other energy sources. The solar fraction, typically more than 0.5, is the percentage of water-heating energy that will be supplied by the sun. It's then calculated into SEF for an overall efficiency that system manufacturers typically report around 2 or 3 of a possible 11.
3. Factor energy efficiency into purchase or installation costs, which may be higher for more efficient systems, and life-cycle operating costs, which should be lower. Use these figures to compare the costs of different new systems you're considering. In the same way, you can compare the initial cost of one or more new systems and their operating costs to what you're paying now for hot water. Divide the initial cost of the new systems (or the difference in initial costs between two systems) by the annual operating savings between systems, and you'll see how soon the new systems will pay back your investment.
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