Legionnaires’ disease: What it is and how you can reduce risks in your home

Becoming educated on what legionella is and how it relates to residential plumbing and radiant heating systems is vital for preventing its growth.

What you need to know about Legionella

Legionella. This term has been in the news, especially after cases of the Legionnaires’ disease in a New York City community and a Las Vegas hotel.

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Legionella is a rare bacteria that can cause Legionnaires’ disease, a severe form of pneumonia, when contaminated water droplets are inhaled. Legionella reproduce in potable water systems with a pH between 5.0 and 8.5. According to OSHA, a temperature of 68° to 122° F (20 to 50° C) is when the bacteria can multiply, while the ideal growth temperature is 90° to 105° F (32° to 40° C). In other words, stagnant hot water in an environment that creates a mist that can be inhaled, your shower for example, can be an “amplifier” for legionella.

What exactly does this mean for you and your home?

There are cases where domestic water heaters have been used as the heat source for smaller hydronic radiant heating or fan coil systems, for instance. It may seem like a good idea or a money saver to have one water heater for two purposes, but the risks that come with this can be high.

The Plastics Pipe Institute in “Recommendation E: Recommendation Against Mixing Hydronic Heating Water with Potable Water,” concludes that designers and installers should avoid specifying or building systems where mixing of hydronic heating and potable water can occur. Having two separate systems allow for the hot water used for radiant heating—that could, though unlikely, be contaminated with legionella– to be contained with that system and not given the possibility to be airborne in your home.

This doesn’t necessarily mean you have to buy two water heaters for your plumbing and heating systems. There are special dual-purpose water heaters intended for supplying both hydronic heating and hot domestic water in a way that the two water streams do not mix. When installed correctly, these dual-purpose water heaters helps prevent the spread of the Legionella bacteria. If your heating system uses your domestic water heater as a heat source, check with your heating contractor to make sure there is no risk that heating water is mixing with potable water in your home.

To learn more about Legionella, Legionnaires’ disease and what you can do to prevent it, visit Legionella.org, Legionnaires’ Disease and Pontiac Fever, and Legionnaires’ Disease.

By David Nickelson, REHAU building solutions technical team leader and REHAU’s representative to Plastic Pipe Institute

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