A tankless water heater (also called instantaneous, continuous flow, inline or on-demand heaters) instantly heat water as it flows through the device. Where the traditional tank-style water heater held 30-50 gallons of water in reserve, the tankless water heater doesn't retain any water internally except for what is around the heat exchanger coil.

Some systems have a tankless heater in a central location (much like the traditional tank style), but most have more than one unit located close to the point of use (POU). A tankless heater might be located in the attic above the bathroom, in the shower itself, or under the kitchen sink. Their relatively small size (about the size of a briefcase) allows a lot of flexibility as to their location.

Tankless units can be split into two categories: "full on /full off" or "modulated." As the name would suggest, a full-on/full-off unit doesn't have a variable output level; it's either on, or it isn't. Modulated tankless heaters base the heat output according to the flow of water running through the unit, modulating the gas valve and outlet so that the user receives the same temperature of water regardless of the flow.

Until recently, most tankless water heaters were electric, but newer models can run on natural gas or propane. Newer models can also deliver as much as 11 gallons of hot water per minute (such as the Noritz 841MC Series), which can meet any hot water needs. Everyone is familiar with the period of waiting for hot water from a conventional water heater, as the cold water in the lines must clear first before hot water comes through. With instantaneous heating from a Noritz tankless water heater, there's no wait for hot water (thereby saving on the water bill). Just one of many good reasons to buy a tankless water heater.

Noritz, in particular, has a dual flame design, with a second row of burners that burn the unburned gas that comes from the first row (all other competitors have a single-burner system). This means more efficient operation and fewer temperature fluctuations.

The heat exchanger of a water heater is perhaps its most critical element, as it is the component that is heated up to conduct heat to the water itself. After countless cycles of heating and cooling down, some heat exchangers can wind up with cracks or leaks. Noritz heat exchangers are made from copper piping that's 25%

thicker than most other brands. Commercial-grade components for residential applications; that's the Noritz design and quality advantage.