Several months after my husband and I and our two kids moved from the US to a space-efficient flat in London, I dragged our contractor into the back of one of our bathrooms to show him a strange, small silver box mounted on the wall and asked if he could remove it. “Not a good idea,” he said. “It’s your water heater.”

Long favored in Japan and Europe where square footage is at a premium, tankless water heaters provide hot water on demand when you need it. 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 our primer to find out if a tankless water heater should be on your house remodeling or tank replacement short list.

Michaelis Boyd Architects Bathroom, Remodelista

Above: A London bathroom by Michaelis Boyd Architects.

With the help of a demure tankless water heater that barely took up any space in our London flat, four of us bathed, showered, washed clothes, and otherwise ran hot water without ever experiencing shortages or wars over water pressure.

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.

Tankless Water Heater Diagram, Remodelista

Above: The inner workings of a gas-powered tankless water heater. Image via Better Water Heaters.

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.

Steibel Tempra Plus Electric Tankless Water Heater, Remodelista

Above: The Steibel Tempra Plus Whole-House Electric Tankless Water Heater doesn’t require venting, which allows for location flexibility.

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. 

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https://homes.yahoo.com/news/remodeling-101-tankless-water-heaters-090000458.html