In short
Air handling unit services cover the planned maintenance, servicing and repair of the AHUs that supply and extract conditioned air in commercial buildings. Engineers check and change filters, inspect fans, belts and motors, clean coils and drain trays, test dampers, heat recovery and frost protection, and verify controls, so the unit delivers the right airflow efficiently and hygienically.
What AHU services involve
| AHU section | What we check |
|---|---|
| Filters | Condition, fit, seals and pressure drop |
| Fans and motors | Bearings, belts and pulleys, alignment, current draw, EC fan operation |
| Heating and cooling coils | Cleanliness, fin damage, leaks, valve operation |
| Drain trays and traps | Blockages, standing water, corrosion, trap seals |
| Dampers | Movement, linkages, actuators, seals |
| Heat recovery | Thermal wheels, plate heat exchangers, run-around coils |
| Humidifiers | Condition, water treatment and hygiene, where fitted |
| Controls | Sensors, frost protection, fan speed control, interlocks |
When AHU work is needed
- planned maintenance visits under your schedule
- rooms feel stuffy, draughty, too hot or too cold
- the AHU is noisy or vibrating
- filter alarms or fan failure alarms on the BMS
- energy use has risen or air volumes no longer match design
Equipment covered
Packaged and modular AHUs, roof-mounted and plant-room units, supply-only and supply-and-extract units, units with heat recovery, and the associated fans, dampers, coils and controls.
Our process
- Share the number, type and location of AHUs, plus any alarms or complaints.
- We survey or attend to service, following the site’s isolation and permit procedures.
- Each unit is inspected, cleaned, tested and recorded.
- Defects are reported with recommended remedies for your approval.
Typical applications
Office floors served by central AHUs, hotel public areas and kitchens, retail sales floors, education buildings and healthcare premises.
Maintenance considerations
- Track filter pressure drop rather than changing filters only by date.
- Keep drain trays draining freely; standing water is a hygiene risk.
- Check belt tension and alignment regularly to avoid premature wear.
- Confirm that frost protection works before winter.
Compliance and safety
Isolate before opening. AHU fans can start automatically under BMS control. Safe isolation and lock-off are essential before any access panel is opened.
Employers must provide sufficient fresh air under the Workplace Regulations. Where an AHU has humidifiers or wet sections, include it in the legionella risk assessment.
Coverage across London
We take AHU enquiries for commercial buildings across London and Greater London. See areas we cover.
Air Handling Units: frequently asked questions
How often should AHU filters be changed?
It depends on the filter grade, the air quality outside, the hours the unit runs and the pressure drop across the filter. Many sites inspect filters monthly or quarterly and change them when the pressure drop reaches the manufacturer's recommended final value.
Why is our air handling unit noisy?
Common causes are worn or slack belts, failing bearings, an unbalanced fan, loose panels, or dampers and ductwork vibrating. Noise often gets worse before a failure, so it should be investigated promptly.
Do AHUs need legionella checks?
Where an AHU has a humidifier, evaporative cooling section or standing water in its drain trays, the legionella risk should be included in the building's risk assessment and controlled as HSE's ACOP L8 describes.
Can you upgrade an old AHU's fans to EC fans?
Fan upgrades to EC (electronically commutated) motors are a common way to cut energy use and improve control. Suitability depends on the unit's casing, airflow requirements and controls, so a survey comes first.
What is included in an AHU service?
Typically filters, fans, belts and pulleys, bearings, motors, coils, drain trays and traps, dampers and actuators, heat recovery devices, frost protection, humidifiers where fitted, and controls and sensors.
UK guidance and references
Primary and industry sources relevant to this subject. Always check the current edition and how it applies to your building.
- Ventilation in the workplace Health and Safety Executive
- Legionnaires' disease (ACOP L8) Health and Safety Executive
- SFG20 standard maintenance specification BESA / SFG20