Long favored in Japan and Europe, where square footage is at a premium, tankless water heaters provide hot water on demand. According to the EPA, residential electric water heaters are the second highest energy users in American households: “The energy consumed by your refrigerator, dishwasher, clothes washer, and dryer combined use less energy than your current standard water heater.” Tankless water heaters offer big savings in energy use and space.

The question is: Can these little units cater to the water-heating needs of larger homes? Read Remodelista’s primer to find out if a tankless water heater should be on your house remodeling or tank replacement short list.

What is a tankless water heater, and how does is work?

Unlike standard water heaters that keep water hot and ready for use at all times in insulated 20- to 80-gallon tanks, tankless models don’t store hot water, they heat on demand. When a hot water tap is turned on, cold water runs through a pipe into the unit where a flow sensor turns on a gas burner or an electric element to heat the water to the desired temperature. When the hot water tap is closed, the flow sensor turns off the burner.

How are tankless water heaters powered?

Tankless water heaters can be fueled by gas (natural or propane) or electricity. Gas-powered units require venting (just like standard tank heaters). Most gas models also have electronic controls, so an electric outlet is needed. Full electric tankless heaters don’t need venting but have minimum voltage and AMP requirements—consult a professional to be sure your power is adequate.

Are there different types of tankless water heaters?

Two types of heaters are generally offered: whole house and point of use. Whole-house systems are powerful enough to generate hot water at flow rates to serve a household. Point-of-use units have low flow rates and are designed to supply hot water for a single appliance or location. These compact contraptions are typically installed directly adjacent to wherever they’re needed, such as under a sink; they’re most often used to augment a system when instant or additional hot water is needed.

How much hot water can a tankless heater generate?

Unlike standard water heaters, which draw on reserves, tankless water heaters provide a continuous supply of hot water. Sound too good to be true? Well, sort of. While the stream of hot water is unlimited, tankless models can only heat and deliver water at a certain flow rate. That output, or capacity, is measured in gallons per minute (gpm). So, while a tankless water heater won’t “run out” of hot water like a storage tank can, there may be an issue of not being able to pump out enough hot water for multiple uses at the same time.

Tankless Water Heater Recap

Pros

• Space savings
• Increased energy efficiency
• Lower operating costs
• Long life
• Constant temperature output
• Endless supply of hot water

Cons

• Expensive
• May not generate enough output for high-use homes
• Electric controls mean no hot water if power outage