Phoenix Journal · Ductwork
The dryer exhaust route you draw at the design stage decides whether a commercial laundry stays cool, efficient and safe - or quietly builds a lint fire risk into the walls. Here is how to plan it properly.
Laundry design
Get the duct routing right on paper and a commercial laundry runs cool, dries fast and stays clean for years - get it wrong and you build a lint-lined fire risk into the fabric of the room.
Whether you are fitting out a care home, a hotel, a hospital linen room or a standalone commercial wash-house, the tumble dryers are the part that shapes everything else. They pull in warm air, drive it through the load and push it out again carrying moisture and lint. That exhaust has to travel somewhere, and the path you draw for it - the length, the bends, the fall, the terminal - is what determines whether the room is safe to work in.
Lint is the problem you are designing against. It is light, it is highly combustible and it settles wherever the airflow slows down: in long runs, in tight bends, behind booster fans and around any restriction. Once it starts to build, airflow drops, drying times climb, temperatures rise and you have created the exact conditions in which normal appliance heat can set the deposit alight. A good route keeps the air moving fast enough to carry lint out of the building rather than letting it collect inside the walls.
Step by step
Work through these in order at the design stage, before the first bracket goes on the wall. Each decision narrows the next, so starting with the appliance data and finishing with cleaning access keeps the whole system coherent.
The headline document for gas-fired laundry equipment is BS 8446:2020, which covers the installation and maintenance of open-flued, non-domestic gas-fired laundry appliances and replaced the withdrawn 2005 edition from 30 November 2020. It is where the single-skin ductwork, the 500mm flexible-connection limit and the 2,000mm terminal clearance all come from, and it applies to both fixed and tilting tumble dryers. Alongside it, the SLEAT code of practice from the Society of Laundry Engineers & Allied Trades is the practical reference many installers work to for exhaust design and lint management.
Those technical standards sit inside a broader legal duty. The Health & Safety at Work etc. Act 1974 requires every employer to keep staff and visitors safe, which includes maintaining ventilation so it does not become a hazard, and the Workplace (Health, Safety and Welfare) Regulations 1992 require workplaces to be properly ventilated with fresh or purified air. A duct packed with lint fails on both counts at once - it is a fire risk and it degrades the air the room is meant to be exhausting. So the routing you design is not only an efficiency question, it is part of how the building meets its statutory obligations.
Design also has to account for the work that will happen around the finished laundry. Any future welding, cutting or grinding near lint-lined ductwork is exactly the kind of task that needs a controlled permit, so if your fit-out or later maintenance involves that, pair the routing plan with a proper safe system of work for hot work. Combustible lint and an open flame in the same void is a combination you plan out deliberately, not one you discover on the day.
Finally, design for the reality that lint never stops arriving. Longer runs and multiple bends collect lint faster, and a busy laundry can move a surprising volume of it in a week. Even a thin coating narrows the effective bore, slows drying and raises running costs long before it becomes a fire risk, so the route you draw should assume regular inspection and cleaning rather than treating maintenance as an afterthought. The best-designed system is the one a cleaning engineer can actually reach along its whole length.
A safe route is only half the job - it has to be kept clear to stay safe. High-volume laundries in hotels, care homes and hospitals typically need the exhaust ductwork cleaned every six to twelve months, more often on long runs with several bends, and a documented clean gives you the evidence trail your insurer and fire risk assessment will look for. Build the schedule in the moment the design is signed off, and the system you drew on paper keeps performing the way you intended.
Questions
There is no single universal figure, because the maximum depends on the appliance - each dryer states its own permitted duct length and equivalent bend allowance, and you design within that. As a fixed rule under BS 8446, though, any flexible exhaust connection should follow the manufacturer's instructions and not exceed 500mm in length. In practice the shorter and straighter the run, the less lint settles and the safer the system stays.
No filters should be fitted inside the exhaust of a gas-fired laundry appliance - BS 8446 calls for single-skin ductwork with a clear path so lint can discharge fully to outside rather than catching internally. Fire dampers are different: where the duct passes through a fire-rated wall or floor they should be fitted as appropriate. Both points are far cheaper to design in at the start than to retrofit into a finished duct.
High-volume operations such as hotels, care homes, hospitals and standalone laundries typically need the exhaust ductwork cleaned every six to twelve months. Long runs with several bends collect lint faster and may need cleaning more often. Keeping a dated record of each clean also supports your fire risk assessment and gives your insurer the evidence trail they expect to see.
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