Demystifying Tankless Water Heater Condensation (Demo)

There’s an aspect of your tankless water heater installation that you may not even realize exists. If you own a condensing tankless water heater, your installer should have included a drainage system to drain your water heater.

Wait a second. Drain your water heater? Why is it leaking? Don’t worry, it’s not leaking, but rather undergoing a normal process called condensation, and Noritz makes the removal process easy with its condensing tankless models.

tankless water heater condensation

What is condensation?

Think back to grade school science class and the three states of water—liquid, solid and gas. Water cycles through these different forms depending on the temperature. For example, when the temperature sinks to 32F, liquid water freezes into ice. At 212F, liquid water evaporates into a gas.

While in its gaseous state, water can turn back into a liquid when it cools to the dew point temperature, which varies depending on the saturation of water vapor in the air. Condensation is the physical process by which a gas turns into a liquid. This liquid is called condensate.

Inside a condensing tankless water heater, the combustion process superheats the water that enters your shower, sink, etc. Water vapor is a byproduct of combustion, although, in this case, the vapor contains elements such as methane, nitrogen and oxygen.

According to Randy Oshiro, Assistant Manager of Engineering at Noritz, when this vapor cools to the dew point temperature, it forms condensate, which must then be drained. This phenomenon is almost exclusive to high-efficiency condensing tankless water heaters.  “In condensing units, the second heat exchanger extracts heat from the combustion gas to enhance energy efficiency, so when the gas rises up the flue, it cools enough to form condensate inside the unit,” explains Oshiro.

Dealing with Condensate

If you have noticed condensate coming out of your condensing tankless unit, hopefully it’s already set up to drain in compliance with local plumbing codes. Contractors need to take condensate removal into account when installing a high-efficiency unit.

Noritz makes condensate removal easy with its condensing tankless models. Inside the unit, a special tray collects the condensate and feeds it to the bottom. At that point, there is a connection for the condensate to be ejected to a floor drain or pumped to an external pipe, depending on local codes.

Note: If improperly drained, the condensate will simply collect on the floor or carpet, so make sure your contractor addresses this. Although only a maximum of two gallons of liquid per hour is released, it will accumulate if improperly drained.

Another consideration when draining condensate is the liquid’s acidity. “Water-heater condensate usually has a pH of two or three,” says Oshiro. “This acid can corrode drain pipe walls over time, leading to permanent damage.” He says one solution is installing neutralizer agent that essentially removes the liquid’s acidity, protecting the pipes from damage. Noritz offers such an agent, the NC-1, as an accessory.

Thus, Noritz solves the condensation problem for you. For more information please visit

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