What are the pros and cons of a tankless water heater? We are considering replacing our gas hot water tank.


What are the pros and cons of a tankless water heater? We are considering replacing our gas hot water tank.

Asked by Beth Bogetich

Our tank in in the semi-finished basement. My 86 year old mother has a "walk in bathtub" we have a dishwasher. What do we look for?

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Danny Kelly's picture

Most tankless water heater brands have very good local product reps. It's best to get them involved rather than letting the plumber choose the size.

Pros of tankless water heating

  • Small and compact, does not take up as much room as a traditional storage tank.
  • Can be mounted on the exterior of the house.
  • "Endless" supply of hot water (under the right conditions).
  • Slightly more efficient (eliminates stand by losses).

Most models now come with an on demand pump which also saves water as there is no longer the need to bleed out the cold water stored in the lines.

Typically tankless heaters are sealed combustion so do not have have the CO and backdrafting issues that are possible with a naturally vented water heater.

Cons of tankless water heating

  • Much more expensive and have a very long payback period.
  • Will more than likely require upgrading the gas line to the water heater, adding a 110 outlet and switching out the vent, all adding more expense and making the payback period longer.
  • Can have some capacity issues if not sized properly and multiple fixtures are being run simultaneously.
  • If a low volume of hot water is desired, some models will not be triggered to turn on for a low flow rate.
  • A tankless will not run if there is a power outage.

What to look for

Traditional storage tank. Look for a direct vent/sealed combustion, high efficiency with good insulation. The better insulated ones made these days do not have as much standby losses as some of the older models.

Tankless.Be sure you select the correct size. It is common to undersize these due to not reading the gallon per minute water output charts properly. Also, need to be sure you have the proper incoming water temperature when figuring the required temperature rise.

For more information:

Check our tankless tips article "Get Optimal Performance from a Tankless Water Heater".