L8/Legionella and HVAC: what facilities teams should know

Legionella control is closely connected to the way a building’s hot and cold water systems are designed, operated and maintained. For facilities teams, heating, plumbing and some HVAC-related equipment can all affect water temperature, circulation and the creation of conditions where Legionella bacteria may multiply.

The HSE’s L8 Approved Code of Practice and associated guidance set out the framework for controlling the risk of Legionnaires’ disease. Building-services contractors can help identify and correct system issues, but their maintenance work should support, not replace, a suitable Legionella risk assessment and management plan.

Where L8 meets building services

Legionella bacteria can grow when water is stored or held at temperatures that encourage multiplication, particularly where the system is poorly circulated or outlets are rarely used. Water droplets or aerosols can then create a potential exposure route, especially in showers, spray taps and certain specialist systems.

Hot water storage and distribution are therefore central to the facilities team’s responsibilities. Calorifiers, hot water return circuits, secondary circulation pumps, thermostatic mixing valves and pipework insulation all influence whether temperatures remain within the intended control range.

Air conditioning equipment does not automatically create a Legionella risk. However, HVAC-related systems such as evaporative cooling equipment, humidifiers or other plant containing water may require specific consideration. The responsible person should ensure each relevant system is included in the overall assessment rather than assuming that routine heating or air conditioning maintenance covers every risk.

Temperature and circulation controls

Hot water is commonly stored at 60°C or above, with hot outlets generally expected to reach at least 50°C within one minute, subject to the system design and suitable scalding controls. Cold water should be kept below 20°C wherever reasonably practicable. These figures are useful reference points, but they must be applied alongside the current HSE guidance, the risk assessment and the needs of vulnerable building users.

Good circulation helps prevent warm areas developing in pipework and ensures the system responds consistently at outlets. A poorly balanced return circuit may leave some branches hot while others remain lukewarm, even when the calorifier temperature appears satisfactory. Measuring at several representative points is more informative than relying on one reading at the plant room.

• Low calorifier or hot water storage setpoints

• Unbalanced secondary hot water circulation

• Oversized storage vessels or long periods of low demand

• Dead legs and infrequently used outlets

• Poorly insulated hot or cold water pipework

Common issues that increase system risk

Building alterations can unintentionally create dead legs, such as capped branches left after the removal of sinks, showers or process equipment. Long runs with little flow can allow temperatures to drift into an unsuitable range. Infrequently used outlets may also need a clear flushing regime, particularly in vacant areas, seasonal facilities or buildings with changing occupancy.

Oversized calorifiers and storage vessels can make temperature control harder because water may remain stored for longer than the system requires. At the other end of the system, inadequate insulation can cause hot water to cool too quickly and cold water to warm up near hot services, plant rooms or poorly ventilated ceiling voids.

Thermostatic mixing valves need particular care. They help reduce scalding risk at outlets, but they can also create areas of warm water if they are incorrectly set, poorly maintained or supplied by a system with insufficient temperature control. Maintenance should consider both safe outlet temperatures and the conditions within the upstream pipework.

How planned maintenance supports early action

Planned heating and plumbing maintenance gives facilities teams an opportunity to spot developing problems before they become larger compliance concerns. A contractor may identify a failed circulation pump, restricted valve, missing insulation, unusual temperature variation or a redundant branch during routine inspections and improvement works.

Useful records should show what was inspected, where readings were taken, the date and time, the equipment condition and any recommended action. If remedial work is completed, documentation should explain what changed, which areas were affected and whether follow-up readings or verification are needed.

These records should feed into the site’s wider water hygiene arrangements. They do not, by themselves, constitute a Legionella risk assessment. Facilities teams should agree responsibilities with the responsible person and use a suitably competent specialist where an assessment, monitoring programme or formal review is required.

Questions to ask your contractor

Before arranging heating or plumbing work, ask how the contractor will work alongside your existing L8 procedures. Clear questions help establish whether the visit will provide useful operational information rather than simply confirm that plant is running.

• Which temperatures, flow conditions or circulation points will be checked?

• Will readings include representative outlets, the calorifier and hot water return?

• What records, photographs or service sheets will be provided afterwards?

• How will dead legs, unused outlets or insulation defects be reported?

• How will remedial works and any follow-up checks be documented?

It is also sensible to confirm whether the contractor is being asked to repair a known fault, investigate a temperature problem or make broader system improvements. This distinction helps avoid confusion over the limits of the work and ensures that any specialist Legionella assessment remains with the appropriate competent person.