Legionella – What is it and why does it matter?

February 8, 2023

We’re taking a deeper look at Legionella and why it matters in our water heating.

If you own a Mixergy tank there’s no need to worry about your settings, and for anyone else thinking about their water heating temperatures please seek professional advice before attempting any changes to your temperature settings.

If you’re a developer or housing provider looking for legionella prevention guidance, head over to our friends Legionella Fire & Services who offer expert and trusted advice.

Legionella is often an undetected bacteria

Legionella bacteria is commonly found in water. The bacteria multiply where temperatures are between 20-45°C and nutrients are available. The bacteria are dormant below 20°C and do not survive above 60°C.

Keeping it at bay is important, as legionnaires’ disease is a potentially fatal type of pneumonia, contracted by inhaling airborne water droplets that can escape from things like air conditioning units, hot tubs, or hot water storage. It’s uncommon but it can be very serious. Anyone can get legionnaires’ disease, but the vulnerable are particularly at risk, for example, the elderly, smokers, heavy drinkers, and those with cancer, diabetes, or chronic respiratory or kidney disease.

This is why it’s a key health and safety concern for owners of conventional water tanks, social housing developments, and those living in older homes. If the water temperature is not controlled properly, there is a risk of it becoming prevalent in the home.

How to prevent legionella in our homes

Legionella bacteria like it when the water storage temperature sits between 20°C and 45°C. To kill it, you need to store water at the right temperature for the right amount of time.

Water stored at 50c kills 90% of the bacteria within 2 hours. At 60°C, 90% die in 2 minutes and then 100% in 30 minutes.

So, keeping the water at these temperatures for a certain time is critical in keeping legionella at bay.

What are the practical solutions to prevent legionella?

Most homes will have either of these two methods for their water needs:

  1. A gas combination boiler with instantaneous water delivery (and other solutions such as an electric shower).
  2. Or a stored hot water tank.

Combination boilers generally pose a low risk due to the nature at which they provide hot water and they do not physically store it. The boiler will quickly fire up and produce hot water at high temperatures. The downside of this method is that combi boilers are increasingly becoming less popular because of their carbon footprint and are being phased out of new build developments by 2025.

The method of storing water in a tank to then be heated by energy has been around for decades and you need to store the water at the right temperatures for the right amount of time to prevent bacteria build-up.

We’re seeing some households turn off their water heating to save money in a midst of an energy crisis. This opens up risks as many aren’t aware of the need to keep their conventional tanks at certain temperatures.

The problem with conventional tanks

Conventional hot water tanks usually have the heat source and coil for the boiler positioned at the bottom of the tank. This design relies on the convection of heat, to transfer the heat from the immersion heater or coil into the water stored within the tank.

This can sometimes lead to an uneven temperature range within the tank, with some areas hotter than others. These conventional tanks also tend to have no real temperature measuring capabilities, so we can’t 100% confirm whether the temperature and the time needed to prevent the bacteria build-up are met.

What can also happen is that these tanks are then “overheated” to greater than >60°C or more, to ensure the bacteria has been killed, which isn’t a smart use of energy. This can also sometimes lead to scalding issues if the appropriate methods aren’t taken to prevent it, leading to further health and safety risks.

Conventional hot water tank heating

How smart hot water tanks can tackle legionella and save energy

Mixergy’s smart hot water technology has solved the problem of killing the legionella bacteria, but optimising the use of energy and saving money. Here’s how it works.

Historically with a conventional tank, you need to heat everything or nothing, there is no in-between.

With Mixergy’s smart hot water technology, typically users only need to heat what they need, resulting in greater energy efficiency. This works as Mixergy’s heat source/s are positioned at the top of the tank and we heat the water from the top-down. This means we can heat what we need, and not the full tank volume. Users can also control their water heating with scheduling and boosting functions, but Mixergy tanks also come with built-in bacteria cleansing cycles.

Mixergy hot water tank heating

A Mixergy tank can also protect against bacteria build-up with temperatures starting as low as 50°C, because of the ability to set temperatures for the correct time periods. And because we can monitor the temperature remotely with sensors, we have greater confidence in our legionella protection.

All Mixergy tanks run a cleansing cycle periodically, during which the tank is heated fully to 50°C, ensuring that all water is safe and free from bacteria. Users don’t need to adjust anything in their settings to ensure they are protected, as the cleansing cycle will automatically run every two weeks. We also don’t allow this cycle to be turned off to ensure no one is put at risk.

How it works with solar PV connections or heat pumps

Solar is becoming increasingly popular as an energy source for the home. The Mixergy tank is ideal for solar as it intelligently shifts heat periods to off-peak at a cheaper rate and will attempt to heat enough hot water each day through the free low-carbon PV generation, using your excess solar energy.

When using a Mixergy tank connected to a heat pump, it will operate at lower temperatures to achieve greater efficiencies, which means we store our hot water at lower temperatures. But with Mixergy, we have a periodically timed legionella process to monitor any growth. And because we can control the temperature, the right temperatures in relation to the right amount of time needed to kill the bacteria is possible, making it the optimal solution to work with heat pumps.

As we move towards sustainable energy sources, we need to consider how our water heating evolves.

Mixergy offers huge energy savings through our smart top-down heating (only heat what you need) and ability to control thermal stratification more effectively than traditional tanks.

And as the energy crisis continues, we can’t forget about the nation’s health whilst trying to save energy and money. Mixergy is the water heating technology that offers the optimal solution for both.

Get in touch with us if you would like to find out more or if you’re ready and would like an estimated quote for a Mixergy tank, simply go to our quote page to find out more.