Tankless
A tankless water heater, also called instantaneous, only provides hot water as needed, saving energy and, therefore, saving you money. They are designed to heat water directly without the use of a tank and are more efficient than conventional water heaters. The primary energy sources for tankless heaters are natural gas and propane. Tankless heaters are typically more efficient than storage water heaters. The absence of a tank saves energy as conventional water heaters have to reheat the water in the tank as it cools off, called standby loss. With a central water heater of any type, water is wasted waiting for water to heat up because of the cold water in the pipes between the faucet and the water heater. This water waste can be avoided if a re-circulating pump is installed, but at the cost of electricity to run the pump and wasted energy to heat the water circulation through the pipes.
Electric Water Heaters
The typical electric water heater is wired to a 220-volt circuit. To heat the water, the current passes through electrical-resistance heating elements—usually two, one at the middle of the tank and one at the bottom. Power is delivered to each element through a thermostat—a switch that senses the water temperature. When the temperature drops, the switch closes to allow current flow, and it opens when the temperature reaches its preset limit. Thermostats have a dial for setting the maximum water temperature–generally between 130 degrees and 140 degrees F, or as low as about 120 degrees F for increased energy savings and scald protection.
When a hot water tap is opened, cold water enters the tank through the dip tube and the drop in temperature triggers the thermostat and element at the bottom. As the water at the top of the tank is replaced by cool water, the temperature at the top thermostat drops, and its element kicks in. When the tap is turned off, the heating elements continue to carry current until the thermostats are satisfied.