You can also install separate tankless water heaters for appliances - such as a clothes washer or dishwater - that use a lot of hot water in your home. However, additional water heaters will cost more and may not be worth the additional cost. To overcome this problem, you can install two or more tankless water heaters. For example, taking a shower and running the dishwasher at the same time can stretch a tankless water heater to its limit. Sometimes, however, even the largest, gas-fired model cannot supply enough hot water for simultaneous, multiple uses in large households. Gas-fired tankless water heaters produce higher flow rates than electric ones. Typically, tankless water heaters provide hot water at a rate of 2–5 gallons (7.6–15.2 liters) per minute. However, a tankless water heater's output limits the flow rate. You don't need to wait for a storage tank to fill up with enough hot water. As a result, tankless water heaters deliver a constant supply of hot water. When a hot water faucet is turned on, cold water flows through a heat exchanger in the unit, and either a natural gas burner or an electric element heats the water.

Tankless water heaters heat water instantaneously without the use of a storage tank.

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