Duct Doctor · London and the South East
Air handling unit cleaning
Air handling units cleaned inside: filter sections, coils, drain trays, fans and internal surfaces, as part of TR19® Air ventilation hygiene.
- Standing water in the drain tray
- Dust and debris on coils and fan blades
- Clogged or overdue filters
What air handling unit cleaning involves
An air handling unit is the heart of a building’s ventilation. It draws air in, filters it, heats or cools it and pushes it through the ductwork to the rooms. Anything that builds up inside the unit ends up in the air people breathe. Dust settles on coils and fan blades, filters clog, and drain trays under cooling coils can hold standing water, which is a hygiene risk of its own. BESA’s TR19® Air covers the hygiene of supply and extract systems beyond the kitchen, and it takes a risk-based, inspection-led approach. We inspect the unit, record its condition with photos, then clean the filter sections, coils, drain trays, fans and internal surfaces. Drain trays are cleared so they empty properly. Our AHU cleaning guide and TR19® Air explained cover the background.
We cover London and the South East, and have done since 2009. We’re a BESCA Vent Hygiene Elite member, cleaning to BESA TR19® Grease, we hold CHAS, SafeContractor and ISO 9001, and we’re fully insured.
Problems we put right
- Standing water in the drain tray
- Dust and debris on coils and fan blades
- Clogged or overdue filters
- Musty smells from the supply air
- Internal surfaces that haven’t been cleaned in years
What we work on
- Filter sections
- Heating and cooling coils
- Drain trays
- Supply and extract fans
- Internal panels
- Dampers and louvres
How it works
- We agree with you which units need cleaning and when they can be switched off.
- Each unit is isolated and we inspect and photograph its condition before we start.
- Filter sections, internal panels and fans are cleaned of dust and debris.
- Coils are cleaned and drain trays are cleared so they drain properly.
- The unit is closed up and restarted, and you get a report with photos before and after.
Drain trays and standing water
Cooling coils produce condensation, which runs into a drain tray under the coil. If the tray or its drain is blocked, water sits there, along with the dust that has collected in it. We clear and clean drain trays and check that they empty, and we’ll tell you if the drain itself needs attention. It’s one of the first things we look at when we open a unit.
Planning around the building
Switching an AHU off affects the rooms it serves. In offices, schools, hospitals and care homes we plan the work for evenings, weekends or holidays, or unit by unit, so people aren’t left without ventilation when they need it. Tell us about any areas with special requirements, such as clinical rooms or kitchens, and we’ll agree the order and timing with you before we start.
Why it’s worth doing now
Everything inside an AHU can end up in the air your staff, pupils, patients or residents breathe. Dirty coils and fans make the unit work harder, and blocked drain trays hold stagnant water. TR19® Air asks building owners to inspect ventilation systems and clean them when their condition calls for it, and to keep records. If nobody can remember when the units were last opened up, an inspection will show what’s inside and what needs doing. It’s far easier to plan a clean now than after complaints about smells or stuffy rooms.
What affects the quote
We don’t publish set prices, because no two systems are the same. Send us a few details and photos, or book a survey, and we’ll give you a fixed price before any work starts. The main things that change it are:
- The size of the system: number of canopies, length of ductwork, risers and fans
- How much grease or dirt has built up since the last clean
- Access: roof-level fans, ceiling voids, risers and how many access panels there are
- When the work can happen: overnight, weekends or school holidays
- Whether extras are needed, such as new access panels, filter exchange or damper testing
- How many sites you want covered on one schedule
What a good quote includes
- A survey or clear photos before the price is given
- Exactly which parts of the system will be cleaned or tested
- How areas that can't be reached will be recorded
- A certificate or written report with before-and-after photos
- Proof of insurance and accreditations you can check
- The recommended date for the next visit
Afterwards
Your report shows each unit before and after, with notes on filters, drain trays and anything that needs repair. Keep it in the building’s maintenance log, so the next inspection has something to compare against. Change filters at the intervals your maintenance contractor recommends, and keep an eye on drain trays between cleans. We’ll suggest when the unit should next be inspected and can remind you when it’s due.
Air handling unit cleaning: common questions
How often should an AHU be cleaned?
TR19® Air takes a risk-based approach: the unit is inspected and cleaned when its condition calls for it. Filters, drain trays and coils usually need attention more often than ductwork.
Do you clean the ductwork from the AHU too?
Yes. We can clean the supply and extract ductwork as part of our ventilation duct cleaning service, so the unit and the ducts it feeds are done together.
Does the unit have to be switched off?
Yes, while we work inside it. We plan the work for times when the rooms it serves can manage without it.
Can you work in hospitals and care homes?
Yes. We plan the work around the building’s routines and agree the times and areas with you before we start.
What do we get after the clean?
A report with photos of the unit before and after and notes on anything we found that needs attention.
Do you give a fixed price before you start?
Yes. Send a few details and photos, or book a survey, and we’ll give you a fixed quote, usually within one working day.
Do you work out of hours?
Yes. We work evenings, overnight and at weekends so your kitchen or building doesn’t lose a day, and there’s a 24/7 line for emergencies.
Page updated 30 October 2026
Near you
We cover London and the South East. Find air handling unit cleaning in your town:
- London
- Brighton
- Southampton
- Portsmouth
- Reading
- Oxford
- Milton Keynes
- Guildford
- Chelmsford
- Maidstone
- Woking
- Crawley
- Croydon
- St Albans
- Canterbury
- Basingstoke
- Slough
- High Wycombe