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Comparing Tank and Tankless
Water Heaters

Understanding the difference between these two ways of heating water is important. Hot water on-demand heaters operate differently, and that difference centers on ground water temperature and the gallons per minute out of the faucet.

The classic storage tank
A standard storage heater offers all the hot water it has, only restricted by the size of the water pipe it travels through. It can produce a lot of water at one time but when it’s gone you wait until it recycles.

The tankless water heater
The performance of tankless heater is controlled by the ground water temperature - the difference between ground water temperature and temperature at the faucet is called temperature rise.

The greater the temperature rise the less gallons per minute are available. Hint: there is no advantage to setting the temperature control higher than necessary.

This loss in gallons per minute can be significant. A model’s literature may quote an output at 6 gallons per minute, this is under ideal conditions. In real life raising temperature from 50 F degrees to 115, for a shower can reduce flow to 2 gpm.

Study the specifications (as in this example) to make sure you’re a buying a heater that is adequate for your local climate and household needs. These measurements are easy to do. All it takes is a thermometer. Note you want run water for a few minutes to refresh the pipe.

Ground water temperature will vary by season, as much as 20-30 F degrees. To reduce the load on a heater in colder months consider ading an inline passive heating element.