Air Handling Units
AHU installation and maintenance for climate-controlled environments.
What we offer
We install and maintain air handling units of every size — rooftop, indoor and bespoke. Filter changes, belt swaps, coil cleans and full overhauls keep your AHU running efficiently.
An air handling unit is plant, not comfort cooling. It is a sectional box — intake and mixing dampers, filter banks, a heat recovery section, heating and cooling coils, attenuators and supply and extract fans — that conditions and moves large volumes of air around a building. You will find them on the roofs of offices and retail units, in dedicated plantrooms, and inside production and warehouse buildings across West Berkshire and North Hampshire. Because they run quietly in the background, they tend to be left alone until the space stops holding temperature.
Filtration is where most AHU performance is won or lost. Filters are classified under ISO 16890 by the fraction of particles they capture — ePM1, ePM2.5 and ePM10 grades — which replaced the older EN 779 G and F classes. Fitting the wrong grade either lets dirt through onto the coils or chokes the unit. Seating matters as much as grade: a bag filter that is not clamped properly lets air bypass the media entirely, so the pressure readings look healthy while the coil behind it keeps fouling.
Fan sections need attention in their own right. Belt-driven units suffer tension loss, pulley misalignment and worn bearings, all of which show as vibration and rising motor current long before anything seizes. Direct-drive plug fans remove the belt problem but still need bearing checks and impeller cleaning, since dust on the blades unbalances the wheel. We record motor current against nameplate, check anti-vibration mounts and flexible connections for splits, and confirm inverter parameters have not been altered — a drive quietly left in hand at full speed is a common find.
Coils foul on the air side and silt up on the water side. Bent and packed fins raise pressure drop and cut heat transfer, so combing and a proper chemical clean often recover more capacity than any control change. On the water side we check strainers, vent trapped air and verify that valves and actuators move through their full stroke. Frost protection deserves a specific test, because if the frost stat or bypass strategy fails on a cold morning a heating coil can freeze and split, and that repair is far more involved than a service.
Heat recovery sections are where efficiency lives. Thermal wheels need their drive belt, bearings, peripheral seals and purge sector checked and the matrix cleaning, because a fouled wheel loses effectiveness gradually and silently. Plate exchangers rely on a bypass damper and control strategy to prevent frosting on the extract side in winter. Run-around coils depend on a circulating pump and a glycol strength nobody has looked at in years. Measuring air temperatures across the section on both airstreams is the quick way to prove what is actually being recovered.
Condensate causes a surprising number of call-outs, and the trap is nearly always the culprit — too shallow, the wrong type, or dried out during a spell with no cooling, so water backs up and overflows the tray. When a unit does reach the end of its life, replacement is not automatic. Sound casework with failed internals is a good candidate for overhaul, with coils, motors, drives, bearings, fans and filter frames renewed in situ. Where panels have corroded through or insulation has broken down, replacement makes more sense, and access usually dictates the programme.
- AHU installation, replacement and in-situ section overhaul
- Filter changes to the correct ISO 16890 grade, logged on differential pressure
- Fan, belt, bearing, motor and inverter drive servicing
- Coil cleaning, condensate trays, traps and frost protection
- Heat recovery: thermal wheels, plate exchangers and run-around coils
- Damper and actuator inspection and sensor checks
- Airflow, pressure and temperature readings recorded against the asset
Common questions
- How often should a commercial AHU be serviced?
- Twice a year is the practical minimum for a general office or retail unit, timed so the cooling side is checked before summer and the heating and frost protection before winter. Units serving production areas, kitchens or laboratories need quarterly attention, and filter changes often fall on a shorter cycle than the full service. Frequency should follow the duty and the environment rather than a template, so we set intervals once we have seen the asset.
- Should filters be changed on a schedule or when they are dirty?
- On measured differential pressure, with a schedule as a backstop. Every filter has a recommended final pressure drop; running past it wastes fan energy and can collapse the media into the coil, while changing far short of it throws away serviceable filters. We record differential pressure across each bank at every visit, so the true interval for your building becomes obvious after a couple of cycles.
- Water is dripping from our AHU or the ceiling below it — what causes that?
- Nearly always the condensate arrangement rather than a leak. The trap draining the cooling coil tray has to be deep enough to overcome the fan's negative pressure. If it is too shallow, the wrong type, or has dried out during a period with no cooling, water backs up and overflows. Blocked drain lines, insufficient fall and corroded trays produce the same symptom, and it recurs if only the puddle is dealt with.
- How can we tell whether the heat recovery is still working?
- By measuring, not by looking. We take air temperatures on both supply and extract sides, before and after the recovery section, and compare effectiveness against the unit's original selection. A thermal wheel that has lost belt tension, worn its seals or fouled its matrix can be turning slowly and recovering very little. Both that and a stuck frost bypass damper show up as higher heating demand downstream rather than as an alarm.
- Can an old AHU be refurbished instead of replaced?
- Frequently. If the casework is sound and the panel insulation intact, the internals can be renewed in place — coils, fan sections, motors, inverter drives, bearings, filter frames, dampers and actuators. Converting a belt-driven fan to a direct-drive plug fan is a common improvement at the same time. Replacement becomes the better route when panels have corroded through or the unit is undersized for how the building is now used.
- Our plantroom has no access big enough for a new unit — is replacement still possible?
- Usually. Modern AHUs are supplied as sections that bolt together, so a replacement can be broken down, carried in through existing doors and corridors and rebuilt inside the plantroom, with joints sealed and the unit pressure tested afterwards. Rooftop replacements are the opposite problem, needing a crane lift, a check on the existing steelwork and roof build-up, and a settled weather window.
Related services
Ventilation Systems
Better airflow and indoor air quality, designed around your building.
Kitchen Extract Systems
Extract systems for commercial kitchens — designed, installed and cleaned.
Service & Maintenance
Planned maintenance that keeps systems running and avoids surprises.
Talk to an engineer today
Free consultation, fast quotes and 24/7 emergency cover.
Areas We Cover
Air Handling Units across Newbury, Reading, Basingstoke, Oxford, London and the wider South of England — covering Berkshire, Hampshire, Oxfordshire, Wiltshire, Dorset and Somerset.