Photograph of an office wall convector air conditioner system Clean & Prevent Legionella
Bacteria in Air Conditioners & Heat Pumps

InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Legionella contamination in air conditioners & heat pumps:

This article explains cause, hazards, & prevention of Legionella bacteria contamination in air conditioners, how to clean air conditioning systems, Legionnaire's disease prevention & cleaning suggestions for air conditioning equipment and condensate trays, including condensate piping, traps, drains, condensate pumps, and concerns for mold, Legionella bacteria, and other hazards associated with air conditioning systems, cooling towers, and evaporative coolers.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

Cleaning suggestions for A/C System Condensate Systems

Photograph of  condensate leaks to interior of blower compartmentHere we discuss cleaning procedures for HVAC equipment in order to prevent Legionella bacteria formation or to remove it if present, a key step in preventing Legionnaires' disease.

Should we disinfect cooling system equipment or condensate trays to prevent Legionella or other bacterial growth?

Should we be putting bromide or chlorine tablets in our condensate trays to keep bacteria from growing?

If we should be, then do we need to alternate bromide with chlorine on some type of frequency to prevent development of resistant bacteria?

[Click to enlarge any image]

We're discussing condensate trays from mechanical equipment like heat pumps, fan coil units and air handlers with AC coils.

These pieces of equipment have condensate trays which are then drained through a small pipe, usually clear, but not always, with a trap in it, to a drain.

These condensate trays have some standing water in them when the AC is functioning. Should these condensate trays be treated with an algaecide of some sort?

There are risks beyond mold and algae, in particular Legionella bacteria (legionnaire's disease) which can have an alarmingly high mortality rate, and also potential hazard sources such as biofilms that can include other bacterial and maybe other pathogens.

However the risk of formation of problem levels of mold, bacteria, or other pathogen is probably not the same across all buildings nor types of equipment, and much of the risk may depend on installation and maintenance details at individual installations.

Particularly in climates with a high humidity and a heavy cooling load, and depending on details of the design and installation of the air handler unit and duct work, there is risk of blowing pathogen-contaminated water droplets downstream inside the air conditioning duct work and thus exposing building occupants.

With rooftop-mounted cooling units such as cooling towers using water, conditions may be still more attractive for growth of pathogens and there is some risk of movement of pathogens out of the cooling equipment to people located nearby and downwind from the equipment, even if they are outside the building which the equipment actually serves.

While I am not expert on this topic I have collected and provide here some key information and opinions to help sort out these questions.

Use the links listed at the "More Reading" links at the bottom of this article to read additional details on this topic including recommended cleaning procedures and details of the Legionella hazard in air conditioning systems, humidifiers, etc.



Continue reading at WISCONSIN PROTOCOL for Cleaning A/C or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see HOT WATER ANTI-SCALD REGULATIONS where we discuss methods for preventing Legionella formation in water heating equipment.

Or see LEGIONNAIRES' DISEASE INFO from CDC health hazards associated with Legionella and other biological contaminants in HVAC systems

Or see this

Article Series Contents

Suggested citation for this web page

Legionella BACTERIA & HVAC Equipment at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


Ask a Question or Search InspectApedia

Try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

HTML Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher's Google+ Page by Daniel Friedman