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Home > HVAC > Need To Know: Legionella and Your Commercial HVAC System

You may be thinking:

What in the world is Legionella?


If you own a corporate building or a multi-tenant building and you’re in charge of maintaining the building, then you should know about this.

Legionella is a bacteria which causes Legionellosis (also known as Legionnaires’ disease).

If you don’t know, Legionnaires’ disease is a form of pneumonia which is characterized by chills, a high fever, coughing, aches, and other terrible symptoms you don’t want to experience. It was fairly recently discovered. In 1976 over 200 attendees of the American Legion convention in Philadelphia became sick–no one knew how or what they had. Of those who were sick, 34 people died from the disease. That’s where it was discovered and where it got its name.

Now why is this important?

Obviously you don’t hear about epidemics of Legionnaires’ disease on the news, you probably didn’t even know what it was, so why does it matter, right?

As HVAC professionals, we learn all about it because it’s essential knowledge in our industry. In 1976 the bacteria spread through the HVAC system of the hotel and infected over 200 people and killed over 30.


The bacteria that causes Legionnaires’ disease is commonly found in cooling towers or commercial-size heating and air systems.

It thrives in warm, stagnant water. And when people inhale the mist or vapor contaminated by the warm air, pushed through the building via the HVAC system, it easily spreads and causes sickness.

Places where the bacteria, Legionella, are often found are in

  • Cooling towers
  • Large air conditioning (HVAC) systems
  • Hot water tanks
  • Hot water systems
  • Ice making machines
  • Humidifiers
  • Whirlpool spas

In various studies, an average of as many as 40-60% of cooling towers tested positively for Legionella. Meaning it is a lot more common than we think!


As a property manager or owner, you have the power to prevent this disease from thriving and spreading in your buildings.

The only way for a person to contract the disease is by ingesting or inhaling the contaminated water vapors or mists, which are spread through poorly maintained HVAC systems. So the main way to protect your building’s occupants from Legionnaires’ disease is by keeping up with your HVAC system’s preventative maintenance.

Scheduling routine, preventative maintenance for your commercial air conditioning systems not only saves you money and extends the life of the system, but it also will save lives. 1 in every 10 cases of Legionnaires’ disease is fatal. Learn more about preventative maintenance for your commercial HVAC system by clicking here.

Never miss an HVAC system maintenance appointment to keep your system clear of Legionella and protect the occupants of your buildings from a deadly disease.