What Are The Main Methods Of Duct Cleaning?

It’s essential to get ductwork cleaned periodically to prevent harmful build up of bacteria and mould but it isn’t something you should tackle yourself.

In order for your ductwork systems to be properly cleaned you will need the services of a professional company who’s registered with the B&ESA (Building & Engineering Services Association) and working to their TR19 standard. Other standards such as CIBSE (Chartered Institute of Building Service Engineers) TM26 and Hospital Technical Memorandum HTM03-1 may also be applicable.

They have a number of cleaning methods, as detailed below, at their disposal and they will utilise their experience to select the most appropriate one for any given application.

Rotary Brush & Vacuum  

This method is particularly useful on dry dust applications which are commonly found in all types of commercial and public buildings. The ductwork system is broken down into workable segments and an access door is fitted at each end. Either side of these doors blocking foam is inserted so that air can only travel in the workable segment. A large and powerful air vacuum unit is then connected to one access door opening whilst a rotary brush is inserted via the other access door. The air vacuum unit is switched on to produce negative pressure inside the ductwork section and the dust, agitated by the rotary brush, is sucked out of the ductwork. It is collected in the air vacuum unit and dust release into the work area is prevented by HEPA filtration.

Air Whip & Vacuum

Often referred to as the “Rattlesnake” due to the noise that the end of the hose causes as it moves down the ductwork. Instead of using a rotary brush to dislodge dust from the internal surfaces of the ductwork a length of hose with an air diffuser on the end has compressed air forced through it. As the air is discharged from the diffuser the dust is moved towards the vacuum unit. This system has particular merit on small cross section ductwork but becomes difficult to control on larger cross sections as the diffuser often leaps back on itself. This leads to increased work times and a reduced uniformity of cleaning along the ductwork. Other disadvantages of this system are the noise it generates and the difficulty of getting a suitably sized compressed adjacent to the work area.

Manual Cleaning

Manual cleaning is particularly useful when the ductwork is too large for either of the two previously mentioned methods or the residue inside the ductwork is sticky and stubborn to move by rotary brush or compressed air.  

Large section ductwork in excess of 800mm diameter or square cannot be effectively cleaned by rotary brush or air whip methods. Provided the ductwork has been installed to DW144 with the correctly specified supports it will support operative entry with tools and a portable vacuum unit to collect debris. It will be necessary for theses operatives to have confined space training certification which permits only one operative inside the ductwork at any time with one other in attendance outside the ductwork ready to assist should any problems occur.

Kitchen extract ductwork certainly falls into the “sticky” bracket of cleaning work. Many alternative methods, such as dry ice freezing, have been tried to find another way of alleviating this onerous task. Hand scraping having applied a degreasing agent remains the tried and trusted method of removing grease deposits which if not addressed can pose a severe fire risk. One other point to note is that this type of manual cleaning will require an access door located every 3 meters along the ductwork run.


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