“Air handler”, “air handling unit”, “AHU” — they all mean the same thing, and they sit at the heart of most commercial HVAC systems. But what an air handler actually does, and how it fits alongside the rest of the heating, ventilation and air conditioning kit in a building, is something a lot of building owners are never really told. Here’s the plain-English version.
What an air handler is
An air handling unit is the box — often a large one — that conditions and moves air around a building. Air is drawn in, treated, and pushed out through ductwork to the spaces that need it, while stale air is drawn back and either recirculated or exhausted. It’s the part of the HVAC system that physically handles the air, which is exactly where the name comes from.
Inside a typical air handler you’ll find:
- Fans to move the air (the biggest energy user — see our piece on running costs).
- Filters to clean incoming air.
- Heating and cooling coils to bring the air to the right temperature.
- Dampers to control how much fresh and recirculated air is used.
- Often heat recovery, capturing energy from outgoing air to pre-treat incoming air.
- Controls linking the unit to the building management system.
Where it sits in the HVAC system
HVAC stands for heating, ventilation and air conditioning, and the air handler is the component that ties those three together. The heating might come from a boiler or, increasingly, a heat pump; the cooling from a chiller or a refrigerant system; but it’s the air handler that delivers that heating and cooling to the building as conditioned, ventilated air. Sit it on a roof or in a plant room, connect it to ductwork and the BMS, and it becomes the lungs of the building.
That central role is why a neglected air handler causes problems that show up everywhere — stuffy rooms, uneven temperatures, rising energy bills — and why keeping it right matters so much.
Packaged or bespoke
Air handlers come as standard packaged units or as bespoke designs built around a specific building’s requirements. Standard units suit straightforward applications; bespoke units come into their own where space, performance or unusual conditions demand it. When we designed the air handling for the offices at Colmore Row in Birmingham, getting the unit matched properly to the building was what made the difference to comfort and efficiency — an off-the-shelf box would have been a compromise.
Keeping it working
Like any major piece of plant, an air handler needs maintenance, occasional refurbishment, and eventually replacement. Looked after, a good unit serves a building for many years; ignored, it quietly costs money and comfort.
We design, install, maintain, refurbish and replace air handling units across the UK. If you’d like to understand what’s serving your building — or you’re planning a new system — get in touch and we’ll talk it through.
