- 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.