Air duct cleaning: a step by step plan for professionals

Step 1: inspection and survey of the duct network

Every job starts with looking. With a camera system you map how dirty the ducts are, where bends, dampers and silencers are located and which material is installed. Where needed you take wipe samples. Cleaning contractors assess that inspection against EN 15780 and against the insurer's requirements and record it in a photo report.

During the survey, pay attention to access. Eurovent advises inspection openings no more than 10 m apart or after no more than two bends of 45 degrees or more. Ducts larger than 500 mm need a hatch of at least 500 × 400 mm, and there should be an opening on both sides of dampers, coils, MVHR units, silencers, filters and fans.

The NADCA standard ACR 2025 also requires a scope of work with a safety plan. It states who does what, which rooms are out of use and how you prevent dust from spreading.

Step 2: sealing valves and closing off duct sections

Before any brush turns, you close off the section you are cleaning from the rest of the building. With duct sealing balloons you shut off a duct section during cleaning or inspection. Foam caps seal valves and diffusers, so that loosened dust does not enter the room. If access points are missing, you fit resealable access hatches or small access doors.

For this, look at the vent caps for duct cleaning in the sealing and extraction category. Work in sections: seal, clean, check and only then move on to the next part.

Step 3: building up negative pressure with HEPA filtration

The most important principle in every professional duct cleaning method: the section you are cleaning is under continuous negative pressure. An extraction unit draws air out of the duct, so that loosened dust goes to the unit and not to the workplace.

• If the extraction unit exhausts inside the building, a HEPA filter of 99.97% at 0.3 µm is required according to the University of Maryland specification.
• The American EPA mentions exhausting to the outside as an alternative.
• Danduct Clean supplies VT extraction fans with hoses and filtration for this purpose.

Negative pressure is switched on before you start and only switched off once the section has been checked. A practical tip: mark on your duct drawing which sections are already under negative pressure, so that a colleague never starts brushing a section that is still open to the room.

Step 4: cleaning with a rotating brush or compressed air

The method follows from the inspection. According to Eurovent, dry methods are usually sufficient for supply and general extract; extract from commercial kitchens requires a wet method.

With the DC4 duct cleaning machine for cleaning contractors you feed the shaft into the duct, and the automatic left and right system changes the direction of rotation in time. Drill driven duct cleaner is intended for smaller ducts. Where you need to get round a corner, choose air nozzle duct cleaning: the Airnozzle requires a compressor of 700 L/min or more at around 10 bar. You choose the brush based on the duct material: soft for fibreglass duct board and sheet metal, more aggressive for stubborn dirt. More on that under air duct brush.

Step 5: checking and measuring after cleaning

Clean is only clean when you can prove it. The common ways:

• Surface comparison: comparing visually or with a camera against a reference.
• NADCA vacuum test: a gravimetric measurement of the dust per surface area.
• Dust density measurement: in German hospital practice under VDI 6022, by inspectors with category A training.
• Grease layer measurement: with a wet film thickness gauge, according to the NVRL quality mark scheme with a sample behind every extract hood and every 10 m of duct; after cleaning a maximum of 200 µm.

For dust, trade publications mention limit values of 0.6, 3.0 and 4.5 g/m² per quality class. Which value applies to your building is explained under rules for clean ductwork.

Step 6: reporting and a file for the client and insurer

The report is the product the client keeps. KHN (Royal Dutch Hospitality Association) states that a clean hospitality duct must be demonstrable with reporting, photos and a certificate. A complete report contains:

1. the scope of the work with a diagram of the duct network;
2. photos before and after for each section;
3. measured values before and after, with the measuring method;
4. deviations, such as damaged ducts or missing hatches;
5. advice for the next inspection.

For care facilities, a German laboratory advises having cleaning and hygiene inspection done by different parties, for objectivity. Set the next moment based on the interval for ventilation duct cleaning that suits the building.

Duct cleaning procedure: checklist for your project plan

Use the checklist per section rather than per building: a large building can have a section that is finished and a section that still waits for hatches. If you are missing equipment for any of these steps, see which ventilation duct cleaning tools suit your ducts.

Common mistakes when cleaning ducts professionally

• No negative pressure: the dust comes loose and spreads through the building.
• Wrong brush: a brush that is too hard can damage fibreglass duct board; the EPA advises soft brushes.
• Biocides without reason: according to the EPA, no biocides are registered for fibreglass duct board and coatings are not routinely needed.
• Compressed air in dusty production areas: in bakeries, Alimento and TNO advise against compressed air for cleaning the room; for ducts under negative pressure the situation is different, but consult your occupational health and safety adviser. See also flour dust in bakery ducts.
• No measurement afterwards: without a measurement you cannot defend the result.

For simple residential systems, part of the work can be done by the occupant. Where that boundary lies is explained under cleaning ventilation ducts yourself.