facebook pixel Tankless Water Heater Buying Guide | HomeTips
Select Page

Tankless Water Heater Buying Guide

How to buy the best whole-house tankless water heater, including selecting the right size, choosing between gas and electric on-demand water heaters, and more.

A whole-house tankless water heater can reduce your water-heating bill by 5 percent to 50 percent or more. As mentioned in How a Tankless Water Heater Works, a whole-house tankless water heater heats water moving through the system instead of heating (and keeping hot) a large tank filled with water the way a storage water heater does.

A whole-house tankless water heater never runs out of hot water. Photo: Rinnai

Water Heater Flow

With a tankless water heater, the supply of hot water can be endless. You don’t empty the water heater with a tall bath because there isn’t a tank to empty. With this type of water heater, the issue isn’t capacity, it’s flow.

A tankless water heater won’t “run out” of hot water unless the flow surpasses the water heater’s ability to heat it.

Think of it this way: If two showers and the washing machine are all running at the same time, a tankless water heater won’t be able to keep up with the flow. It simply cannot heat the large volume of water that is passing so quickly through it. So, it will deliver lukewarm water. Then again, if you buy a unit that puts out a lot of heat and you stagger showers and washing machine usage by a couple of minutes, you won’t have a problem.

You can fill an oversized bathtub when you have this type of water heater but not when another appliance or fixture is using hot water—and, if the tub has a supply designed to deliver a very high flow rate, you may have to slow down the water a little. (If you have a tankless water heater and you’re in the market for a new dishwasher, consider a dishwasher that heats its own water.) Aside from staggering usage, the key is to size a tankless water heater properly for your needs.

Tankless Water Heater Types

Because of the heat output and response time required, most whole-house tankless water heaters have burners that are gas-fired (including propane or kerosene). Gas-fired tankless water heaters require venting—in fact, their flues generally must be larger than those required for gas storage water heaters. Some units have power vents that allow you to exhaust gases out a side wall; these are ideal for situations where running a new vent out the roof would be impractical. Rinnai, Bosch, and other companies also make units that can be installed outside the home and therefore do not require venting (these may not be practical in extremely cold climates).

Some models have pilot lights; others have electronic ignition that may require electrical hookup. One Bosch tankless water heater utilizes “hydro ignition,” a tiny water-powered turbine that sparks the burner. Models that don’t require a pilot light are more expensive but also more energy efficient.

If you need to fit the unit into a tight space, such as an attic, look for a “sealed combustion” model that is compact in size. Rinnai tankless water heaters utilize a cool-to-the-touch vent system for just such situations.

Tankless Water Heater Warranties

Be sure to check out the product’s warranty. Unlike conventional water heaters with tanks that deteriorate after years of storing mineral-laden water, tankless water heaters offer long-term reliability. The critical component is the heat exchanger. Warranties on this part run from five to twelve years.  You can shop for tankless water heaters online at Amazon.com.

NEXT SEE: How to Size a Tankless Water Heater


About Don Vandervort
Author Image
Don Vandervort developed his expertise more than 30 years ago as Building Editor for both Sunset Books and Home Magazine. He has written more than 30 home improvement books and countless magazine articles. He appeared regularly on HGTV’s “The Fix,” and served as MSN’s home expert. Don founded HomeTips in 1996.

Related Posts:

Join the Conversation


  1. I have 3 1 bedroom and 2 two bedroom units in one building. As I am in Southern California I am acutely concerned with water use especially the water that is wasted while heating up for a shower or doing dishes.
    Would a gas fired whole house instant water heater be right or should I install individual water heaters for each unit? Normal occupancy is about two people per unit so it would be for 10 people using water to shower and wash

    • Doesn’t sound like the right solution. Tankless water heaters cannot serve several showers and water-using appliances simultaneously. You might want to investigate a recirculating pump or, for the sinks, on-demand water heaters located beneath the fixtures.

  2. Great info. I had to replace my water heater a few months back and didn’t know enough about tankless ones to go that route. Next time I’ll know better what I’m up against.

  3. Nice informative post. Thanks.


Submit a Comment

Your email address will not be published. Required fields are marked *