Natural refrigerant heat pumps: an effective means of reducing the risk of Legionnaires Disease

Heat Pumps using the natural refrigerants CO2 or R290 – such as our ECOMOD CO2 and ECOMOD 290HT – are not only a more environmentally friendly and energy efficient alternative to gas boilers, but did you know they are also highly effective in preventing the spread of Legionella bacteria in domestic hot water (DHW) applications?

What is Legionella?

Legionella pneumophila is a bacterium commonly found in natural water sources such as rivers, lakes and reservoirs.  Usually, its presence in these natural settings is in low numbers, which means it does not represent a health risk to humans. 

What is Legionnaires Disease?

Legionnaires Disease is a lung infection caused by inhaling droplets of water containing high concentrates of Legionella bacteria.  You cannot usually get it from drinking water that contains the bacteria or from other people with the infection.

How dangerous is Legionnaires Disease?

Legionnaires Disease is a potentially fatal form of pneumonia. Whilst everyone is susceptible to the disease, some groups of people are at greater risk:

  • over 45’s
  • smokers and heavy drinkers
  • people with chronic respiratory or kidney disease
  • people with diabetes, lung and heart disease
  • anyone with an impaired immune system

Where is Legionella most likely to be found?

In low numbers in natural settings, Legionella is rarely a risk to health.  Where it becomes problematic is in purpose-built systems where water is maintained at a temperature high er than that of the incoming water.  Other factors that contribute to its growth are the presence of nutrients such as rust, sludge, scale, organic matter and biofilms; and systems that store and/or re-circulate water where there is insufficient flow.  Typically, this includes hot and cold water systems (especially via taps and showers that are used infrequently), spa pools and hot tubs, air conditioning systems and humidifiers.

At what temperature does Legionella grow rapidly?

Legionella pneumophilia bacteria grow in a wide water temperature range of between 20-45°C.  The bacteria are dormant below 20°C and do not survive above 60°C. 

How do I prevent Legionella in hot & cold water systems?

Water temperature control is most effective method of controlling the risk from Legionella.  The Health & Safety Executive recommend water services should be operated at the following temperatures:

  • Hot water storage cylinders (calorifiers) should store water at 60°C or higher
  • Hot water should be distributed at 50°C or higher (thermostatic mixer valves need to be fitted as close as possible to outlets, where a scald risk is identified).
  • Cold water should be stored and distributed below 20°C.

Organisations have a duty to prevent the growth of Legionella under the Health and Safety at Work Act 1974.  Penalties for failure to comply can be stringent.

Can heat pumps prevent Legionnaires Disease?

Heat Pumps usually operate at a lower temperature than boilers – around 50°C – which means they are not effective at eliminating Legionella bacteria, when used for domestic hot water production.  However, the new breed of natural refrigerant heat pumps, especially those that use R290 or R744 natural refrigerant, can achieve flow temperatures up to 75°C and 70°C respectively. When the water is kept at these constant temperatures Legionella bacteria will swiftly die.

Our new natural refrigerant heat pumps use R290 and R744 natural refrigerant.  As the name implies, the ECOMOD 290HT uses R290 refrigerant and is available in three chassis sizes and five outputs from 15kW through to 50kW.  ECOMOD CO2 heat pumps use R744 and come in three outputs - 65kW, 95kW and 130kW.  Even higher outputs are possible on both types, when installed in a cascade arrangement, where up to six can be centrally controlled, operating from an intelligent lead controller.  

A further plus to using a natural refrigerant heat pump system is that it often requires less amendment to the hot water cylinder, as they do not require immersion heaters for pasteurisation cycles due to the consistent higher temperatures which are achievable.

Safety first

With the high temperatures achievable with a natural refrigerant heat pump, it is important to include a central plant domestic hot water mixing valve  (also known as a blending valve or tempering valve).  This will efficiently temper down hot water to safe usage levels, avoiding scalding users with very hot water.

For more information on the current standards relating to this topic visit:

•            ACOP L8 (HSE)

•            BS 8558: 2015

•            BS EN 806 – 2 - 2005

To find out how natural refrigerant heat pumps can help reduce the risk of Legionella in your DHW system, contact your business development manager.

Related products

  • Ecomod 290 Ht Cascade V2 Web

    ECOMOD 290HT

    The ECOMOD 290HT range of commercial heat pumps come in three chassis sizes and five outputs: 15kW, 18kW, 27kW, 40kW and 50kW.

    Featuring R290 natural refrigerant for ultra-low GWP of 3 they are able to achieve high temperatures up to 75°C.

    View product
  • Ecomod Co2 Coq Heat Pumps 2 V2


    The ECOMOD CO2 & CO2Q range of commercial heat pumps come in three outputs: 65kW, 95kW and 130kW

    Featuring R744 (CO2) natural refrigerant for ultra-low GWP of 1 they are able to achieve high temperatures up to 70°C.

    View product