These systems are designed to move hot water from your water heater to your most remote fixture within seconds. At the push of a button the cool water you normally let run down the drain is circulated back to the water heater through the cold water line so it isn’t wasted. Systems can easily be installed under the sink farthest from your water heater.
Systems can be activated by an on/off button, motion sensor, thermostat or timer. Thermostats or timers automatically turn on the pump whenever water temperature drops below a set-point, or when the timer reaches a setting. Although these systems ensure that hot water is always available at the faucet without any waiting, they may use more energy than an on/off button due to more frequent recirculation cycles.
For more information, see H2OUSE.org and CUWCC Hot Water Articles
While limiting wait time these may or may not help with water conservation. These can be installed with gas/propane or electrical connections. They do not require a tank for storing and maintaining hot water. Water is heated instantly and on demand only, eliminating the need to store and constantly heat water. Tankless water heaters can provide an endless supply of hot water which means the capacity of your water tank does not limit the use of hot water.
- Simultaneous Water Usage Needs
Do you need to run 2 showers at the same time or maybe a shower and a couple sinks? Use a 2.5 gpm flow rate for a shower and 1.0 gpm for a lavatory sink as a reference point to determine your total simultaneous water needs. For example, if you are running 2 showers at the same time, you will be requesting 5 gallons per minute from the tankless water heater. If you were running a shower and the washing machine at the same time, you would be requesting 5 ½ gallons per minute from the water heater. In either of these situations, you would need something that produces at least 5-5 ½ gallons per minute.
- Gas vs. Electric
Sometimes you have a choice between gas and electric. The gas units are typically more powerful than the electric units and are more energy efficient. The most important considerations for a gas installation are the venting, proper gas line sizing, combustion air requirements and venting of combustion gases. The electric tankless water heaters are hard wired and typically have high amperage requirements; however, there is no combustion air or venting requirement with an electric unit. This means an electric unit can be cheaper to install, but remember that electricity is a more expensive form of energy than gas.
For more information, see Energy Star Tankless Water Heaters.