Turning Down the Heating to Save Energy? Don’t Forget Legionella

Why this matters: the temperature range

Legionella bacteria multiply in water that sits in a warm range and are controlled by keeping hot water hot and cold water cold. That is why national guidance, including the HPSC National Guidelines for the Control of Legionellosis in Ireland (2009), focuses on temperature control as one of the main ways of managing the risk. Turning hot water down to save energy can move parts of your system into the range where bacteria grow more easily, so any change should be assessed first, not guessed.

Where energy-saving measures can create a problem

• Lowering the calorifier or cylinder setpoint. If stored hot water is no longer held hot enough, the base of the vessel and the pipework can sit in the wrong range.
• Switching off recirculation pumps. The loop that keeps hot water moving may be turned off overnight or at weekends to save electricity, leaving water to cool in the pipework.
• Removing or shortening insulation, or leaving pipework uninsulated after maintenance, so hot lines lose heat and cold lines warm up.
• Cold water stored in warm plant rooms or lofts, where it can pick up heat. Our article on plant rooms and the risks of poorly managed plant is a useful read.
• Reduced use. Energy savings often go hand in hand with quieter buildings and fewer outlets used, so water stagnates. See our guide to biofilm.

What to do before changing any setting

1. Check your current written scheme of control and risk assessment for the temperatures you are meant to be maintaining.
2. Ask your risk assessor or water hygiene contractor to confirm that the change will not affect Legionella control, in writing.
3. After the change, record temperatures at the calorifier, at the return and at sentinel outlets, and keep the readings in your logbook. Our logbook guide explains what to keep.
4. Look for energy savings that do not touch Legionella control, such as better insulation, controls and servicing.
5. Review the risk assessment if the system or how it is used changes.

Your duties

The Safety, Health and Welfare at Work Act 2005 requires employers and those in control of workplaces to manage risks from their water systems. A cost-saving measure that weakens control is not a defence if someone becomes ill, so it is worth getting the balance right and recording the reasoning.

If you are unsure whether your system still meets your risk assessment, a review of your Legionella risk assessment, with sampling where appropriate, will tell you where you stand.