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Except for the furnace or boiler that heats the house, the largest energy consumer in most homes is the water heater. Typically it keeps a 40- to 60-gallon tank of water hot 24 hours a day. Yet the average household uses hot water no more than two hours a day. Worse still, in homes with dishwashers, the temperature must be held 30° to 40° F. above the normal 100° temperature used for showers and sinks; otherwise, cooking fats and greases won’t dissolve. Europeans long ago remedied this energy-wasteful setup with on-demand water heaters, compact devices made without the traditional storage tank. On- demand heaters use highly efficient heating coils and heat-exchange chambers to raise water temperatures only when the water is turned on. Now available in the United States and Canada, these heaters can be fueled by natural or propane gas or by electricity. The larger gas-fired models can meet the hot-water needs of a small house or a vacation cottage, but they are expensive. Also, the natural-gas versions must be connected to gas lines by a professional plumber. The smaller electric models (right, top) generate only enough hot water to ser vice a single plumbing fixture or appliance, but they are cheaper and can be installed by anyone familiar with basic plumbing and wiring techniques. How ever, you may need an electrician’s guidance in connecting the power circuit to the main electrical panel. Small electric on-demand heaters can be a convenient solution if you need additional hot water for a new bathroom or laundry room. They can also be used in conjunction with an existing water heater to boost water temperatures at specific locations. For instance, if you install one near a dishwasher, you can turn down the temperature at the main water heater to 100° and raise it to 140° just as the water enters the dishwasher. Small on-demand heaters also reduce the heat lost by hot water traveling through long lengths of pipe. Although on-demand heaters save energy costs, the exact amount they save depends on several variables, including the type of heater you choose, the type of heater you currently use and the relative cost of the various forms of energy in your area—gas, oil, electricity. Manufacturers estimate that you can save 22 per cent or more by switching from a conventional electric water heater to a series of on-demand electric heaters. If you use an on-demand heater to supplement an existing heater, you can probably cut your heating costs about 5 per cent for each 10° you lower the temperature at the main heater. Savings in energy will also come from an inevitable change in water-use habits. On-demand heaters raise water temperatures in inverse ratio to the rate of water flow: The faster the water flows through the unit, the less heat it picks up. At 2 gallons a minute, the maximum rate of flow through most electric on-demand heaters, the water temperature will rise only 30°; at the slower rate of ¾ gallon a minute, the temperature will soar by 90°. In winter, when the water entering the unit is colder, the flow rate may have to be decreased even further to achieve suitably high temperatures. To accommodate the lower flow rates, you will have to install low-flow shower heads, which can operate satisfactorily on less than 2 gallons of water a minute, and low-flow faucet aerators, which re quire as little as half a gallon a minute. By putting a squeeze on the flow, these de vices save water as well as the energy used to heat it. Since many on-demand heaters are manufactured overseas, make sure that the installation procedures for the unit you choose comply with local building codes in the United States or Canada. If in doubt, check with your local plumbing or electrical inspector. In addition, make sure that gas models have been certified by the American Gas Association or the Canadian Gas Association, and that electric models bear the Underwriters Laboratories or Canadian Standards Association seal of approval. 110 ___How an on-demand heater works. With its plastic cover removed, an on-demand water heater looks more like a small engine part than a sophisticated electrical device capable of heating 100 gallons of water per hour. The key to this remarkable efficiency is the unit’s cylindrical heat- exchange chamber, shown with a portion of its wall cut away to reveal the coiled, copper- sheathed heating element inside. The heating element draws current from the terminal block, to which the electric power cable is connected. Water entering the unit through the water inlet automatically activates a flow switch to complete the electric circuit. The water enters the heat-exchange chamber through a pipe at lower right and is heated by the copper coil as it rises to the top of the chamber. There, an open-ended copper drain tube draws off the hot water, channeling it down through the center of the heating element and through the hot-water outlet. The unit’s performance is regulated by an electronic heat- sensing element, or thermistor, at the top of the chamber. The thermistor monitors the temperature of the water, comparing it with the temperature that has been set on the unit’s thermostat adjustment dial. If the desired temperature can be reached without constant consumption of power, the thermistor overrides the flow switch and shuts off the power, switching it back on only as necessary. A thermal cutout, also mounted at the top of the heat-exchange chamber, prevents water in the chamber from overheating if the water supply is interrupted for any reason. The cutout shuts off all power if the temperature of the heating coil reaches 190° or the water temperature exceeds 160°. Additional protection against temperature and pressure build-up is provided by a relief valve, which should be installed on the water-outlet line as shown below. —TERMINAL BLOCK; -THERMOSTAT ADJUSTMENT DIAL; LOW SWWCH ___Plumbing connections. A vertical length of copper tubing is first connected to the heater’s water inlet with a two-piece compression f t ting, consisting of a threaded nut and a soft brass ring. To make this connection, place the nut and then the ring onto the tubing, and push the tubing into the inlet as far as it will go; tighten the nut to the inlet, compressing the brass ring against the tubing. A shutoff valve is added near the heater, and the plumbing is then ex tended back to an existing water line with appropriate fittings and lengths of tubing. A preassembled pressure-relief fitting, provided with the heater, is attached to the water outlet with a compression fitting, as above. Then a relief valve, rated to open at 150 pounds per square inch of pressure or 210° of temperature, is turned into the threaded horizontal opening in the pressure-relief fitting, and threaded pipe is added to the valve to channel released water down ward. Finally, the outgoing water line is extended to the plumbing fixture or appliance. This line, too, needs a shutoff valve, so that the unit can be fully shut down for servicing. Before the final connections are made, however, the water flow must be adjusted as shown. 111 Turning On Power and Water Wiring the heater. Most electric heaters re quire a 240-volt power supply to carry the 30 to 40 amperes of current needed to heat the water, and must be wired directly to the main electrical panel. Run plastic-sheathed copper cable—No. 10 for 30 amperes, No. 8 for 40 amperes—from the main electrical panel to the heater, but leave the circuit unconnected at the main panel. At the heater, strip the cable sheathing and the ends of the two insulated wires; trim all three wires to the same length. Loosen the cable clamp at the lower right of the heater, and pull the cable through the opening. Loosen the three screws on the lower part of the heater’s electrical terminal block, and line up the ends of the wires with the corresponding terminals on the block—the bare ground wire with the ground terminal on the left, the insulated black and white wires with the terminals marked L-1 and L-2 (either wire can be connected to either terminal). Then forcefully push the ends of the three wires into the spring-loaded clamps in the terminals, and tighten the three screws to hold the wires securely in place. Don’t make the connection at the main electrical panel until you have checked the plumbing for leaks and adjusted the water flow. Adjusting the water flow. After the incoming water line is hooked up, place a 1-gallon container, such as a plastic milk bottle, under any convenient connection on the outgoing line, and set a pan underneath to catch any overflow. Open the shutoff valve on the incoming line fully, and have a helper turn on water to the new line at the nearest shutoff valve or at the main valve. Measure the time it takes for the container to fill; have your helper turn off the water. Compare the measured rate of flow with the flow recommended for your particular installation. To adjust the flow, close the heater’s incoming water valve a half turn and have your helper turn on the water; re-measure the rate of flow. Ad just it in this manner until the proper flow rate is reached. Then, leaving the incoming water valve in position, shut off the main water sup ply and connect the heater’s outgoing water line to the plumbing fixture or appliance. Turn on the main water supply again and check the new plumbing for leaks. If you are expert in electrical work, connect the 240-volt circuit to the main electrical panel; otherwise, have a professional electrician make this connection. Turn on power to the heater. Set the water temperature b turning the screw on the thermo stat adjustment dial and checking the heated water with a thermometer. Attach the cover to the heater with the four screws provided. [112 ] A Timer That Saves Current Conventional electric water heaters are undiscriminating consumers of electricity, keeping a tankful of water hot even when no one is home to use it. But such profligacy is readily avoidable: An inexpensive timer switch, similar to the kind that turns lights on and off, will program the water heater to warm up its contents when you need it and shut itself off for the rest of the day. Water-heater timers are available at department or hardware stores. Be sure to select a timer that has voltage and watt capacity matching those of your water heater. Most electric heaters will re quire a 240-volt, 10,000-watt timer, the type shown. To install the timer, you will need only the most basic wiring skills and a few electrical tools and materials. The most important tool is a voltage tester to check that the current is off before you touch any hot wires. You will also need plastic-sheathed indoor cable to reach from the top of the heater to the spot where you plan to mount the timer—on a stud or joist as close to the heater as possible. Select cable that has a ground wire and that matches the gauge of the cable connecting the heater to the main electrical panel of the house. To cut and strip the cable and its wires, you will need a cable stripper and a wire stripper. Buy two cable clamps to match the cable gauge and a few cable staples to anchor loose cable to studs or joists once the installation is complete. To operate the timer, you must set the clock to the actual time of day, and then fasten trippers at selected hours around its rim. As the clock rotates, the trippers flip a switch that shuts the current on and off at the times you have specified. You will get the best results if you set the timer to switch on one hour before hot water is needed in the morning, and off as soon as it’s no longer being used; then on again one hour before evening use and off for the night. For maximum savings, try to hold the total “on” time to no more than three hours. Insulation will make the system even more efficient; with an insulated water heater, the water in the tank will stay warm enough to heat up fairly quickly. If your water heat is not insulated al ready, it’s best to put the insulation in place before you install the timer. You should also add loam insulation to all exposed pipe runs. 1. Testing a circuit for safety. Cut off the cur rent to the water heater at the service panel, either by flipping the circuit breaker or by unscrewing the fuse. Then, at the water heater, unscrew and remove the small metal plate covering the lead wires that connect the heater to the wires of the incoming power cable. Twist off the wire caps that join the two sets of wires, taking care not to touch any exposed wire. Set the tester probes against the twisted ends of the hot wires. Then set one probe against each twisted wire in turn while holding the other probe against the ground wire. None of the three tests should produce a light in the voltage tester. If the tester lights up even once, you have disconnected the wrong circuit at the service panel. Continue to test until you find the correct circuit. When the power to the water heater has been shutoff, detach the ground wire and untwist the heater leads from the incoming power wires. Loosen the cable clamp around the power cable, and pull the cable free of the heater. [113 ] 2. Preparing the timer for installation. Open the door of the timer box, and press the spring lock at the top of the box with one hand to release the timer clock. Hold the lock down while you lift and tilt the rim of the clock with the other hand, freeing it from the box. Punch out the two knockout holes in the bottom of the box, and insert two cable clamps through them; be sure the heads of the clamping screws face front, for ease in tightening later. Anchor the clamps to the inside of the box with star nuts, tapping each point of the star with a nail set and a hammer to tighten the nut against the box. Pry up the door latch so that it will be in the proper position to slip into the door slot. Then use the keyhole openings at the back of the box to fasten the box to a stud or joist near the water heater and within reach of the in coming power cable. Replace the timer clock in the box by sliding it into the top of the opening and snapping it in place. Pull off the protective plastic cover that insulates the timer terminals. [114 ] 3 Connecting the power cable. Cut a piece of cable long enough to reach from the timer box to the leads on the top of the water heater. Strip approximately 4 inches of sheathing from each end of the cable and 1 inch of sheathing from the end of each of the wires inside the cable. Then push one end of this length of cable up into the timer box through the cable clamp beneath the terminals marked LOAD. Keep pushing until the cable sheathing bumps against the box, and tighten the screws of the cable clamp. Then slide the ends of the two hot wires up into the slots behind the terminals, and tighten the terminal screws. Fasten the wires of the incoming power cable to the terminals marked LINE in the same manner, tightening the cable clamp around the cable as before. Then crimp the two ground wires together with a wire cap, adding a short length of connector wire, and fasten the connector wire to the ground screw. 4 Connecting the timer to the heater. Run the remaining cable end into the access hole at the top of the water heater, and anchor it at the access hole with a cable clamp. Connect the two cable wires to the water-heater leads with wire caps; twist the caps clockwise until they are tight. If bare wire remains exposed, remove the cap, cut the wires and twist the cap back on. Connect the ground wire to the ground screw. Then replace the metal plate that covers the wires. Set the timer clock and trippers according to the manufacturer’s instructions. Push the timer switch to ON and replace the protective plastic cover that insulates the terminals. Close the timer door and put a padlock through the latch. Before turning the current back on, be sure all loose cable is anchored to solid surfaces with cable staples. [115] Prev | Next: Backyard Alternatives to Store-bought Electricity |