How often is duct cleaning required?

Why a blanket interval fails

A twelve-month interval applied across an estate will over-service some systems and dangerously under-service others. A supply system in a low-occupancy office with good filtration may hold condition for several years. A grease extract system above a wok range running seven days a week can become a genuine fire risk within three months.

Setting frequency properly means measuring how quickly each system loads and scheduling on that basis.

What drives frequency

• System type — supply, general extract, kitchen grease extract or process LEV
• Usage intensity and operating hours
• Filtration quality and how reliably filters are changed
• Occupancy density and the activity taking place in the space
• External air quality at the intake, particularly on urban and roadside sites
• Measured contamination at the last inspection, which is the strongest single indicator

Typical starting points

As a rough guide before survey: heavy-use commercial kitchen extract is often quarterly; moderate-use kitchen extract six-monthly; light-use kitchen extract annual. General supply and extract ventilation in commercial buildings is commonly inspected annually and cleaned when inspection indicates it. Healthcare and controlled environments follow the requirements set out in the relevant health technical memoranda. Industrial LEV is driven by process loading and can be anything from monthly to annual.

These are starting points for scoping a survey, not recommendations for your building.

The practical approach

Establish baseline condition across all systems, set an initial frequency from the measurements taken, then adjust after the next inspection based on how much the system actually loaded in the interval. Within two cycles you have a defensible, evidence-based schedule that avoids both unnecessary spend and unmanaged risk.