Phoenix Journal · Ductwork
When a laundry room runs hot all day, the dryers are rarely the fault - a narrowed, lint-loaded extract duct usually is. Here is what the heat is telling you.
If your laundry room feels like an oven by mid-morning, the machines are not the whole story - the way their heat is meant to leave the building usually is.
A commercial laundry is one of the few rooms in any building designed to run hot on purpose. Tumble dryers heat air, tumble it through a load, then push that warm, moisture-laden air out through a duct to the outside. When that path works, the room stays merely warm. When it does not, every degree the dryers produce stays trapped indoors, and you end up working in the heat the machines were supposed to be venting away.
The frustrating part is that a hot laundry room is rarely a fault with the dryers themselves. Far more often it is a sign that the extract path has quietly narrowed, and the heat you can feel is the first clue to a problem you cannot yet see.
The heat in numbers
A tumble dryer does not simply warm your washing - it moves a large volume of hot air through the drum and out the back. Peak exhaust temperatures on a hard-working commercial machine can approach 93°C as the air leaves the cabinet, carrying both heat and water vapour with it. In a well-set-up room, that air travels straight down a clear duct and out through the wall or roof, taking most of the warmth and nearly all the moisture with it.
Two things have to be true for that to happen. First, the duct has to be genuinely clear, so the fan or the dryer's own blower can shift the full volume of air it was rated for. Second, the room needs enough replacement air coming in to make up for everything being pushed out. Extract and make-up air work as a pair - pull a large volume out of a sealed room and the dryers start fighting a vacuum, which slows the airflow and pushes the heat back at you. When either half of that pairing fails, the symptom is the same: a room that climbs in temperature through the day and never quite recovers.
The most common reason the extract path narrows is lint. Every load sheds fine fibres, and although a lint filter catches the worst of it, a steady fraction escapes past the filter and settles along the duct - especially on bends, in flexible sections, and anywhere the run is long. It builds slowly and invisibly, so nothing looks wrong from the outside. Inside, though, the effective diameter of the duct is shrinking week by week, and the dryers are being asked to breathe through an ever-smaller straw.
As the airflow drops, two things happen at once. The dryers hold their heat for longer because they cannot vent it, so their cabinets and the surrounding air run hotter. And the machines take longer to finish each cycle, which means they spend more minutes per load pouring heat into the room. You feel both effects together: a warmer room and dryers that seem to run and run. Many operators respond by turning the dryers up or running them harder, which only adds to the heat load and disguises the underlying restriction.
There is a limit to what airflow alone can fix, too. If the room was never given adequate make-up air, or if a replacement grille has been blocked off or a door kept shut that used to stay open, even a spotless duct will struggle. It is worth checking both sides. But in a room that used to cope and has gradually turned into a sauna, a loaded extract duct is the usual culprit, and it is the half you cannot see by looking.
Lint is not a neutral nuisance. It is highly combustible, and a warm duct packed with it is one of the most common and most preventable causes of laundry fires. UK fire and rescue services regularly issue warnings to businesses on exactly this point, because a restricted, lint-lined duct combines fuel, heat and reduced airflow in a single hidden space. The rising room temperature you notice is the mild, early version of a risk that gets sharper the longer the duct is left.
There is a legal dimension as well. The Workplace (Health, Safety and Welfare) Regulations 1992 require workplaces to be effectively ventilated with fresh or purified air, and dryer extract falls squarely within that. The Regulatory Reform (Fire Safety) Order 2005 puts a duty on the responsible person to identify and control fire risks, and a combustible-lined duct is precisely the sort of hazard that duty is meant to catch. Keeping the extract clear is not only about comfort - it is part of meeting obligations that sit on the employer under the Health & Safety at Work Act 1974 and the fire safety order together.
All of which is why an overheating laundry deserves more than a fan in the corner. The comfortable, compliant and safe fix is to restore the extract to the state it was designed for - a clear duct moving its full rated volume of air, paired with enough make-up air to let it. A proper clean removes the lint from the full run, including the bends and flexible sections where it concentrates, and a good report tells you how heavily it had loaded so you can set a sensible interval. For a high-use room, that is commonly every six to twelve months; longer, twisting runs may need it more often. The same principle applies right across a hot working building - our guide to why a commercial kitchen runs so hot comes back to the very same pairing of extract and make-up air.
Questions
Tumble dryers push out large volumes of very hot air - approaching 93°C as it leaves the machine - which is meant to travel down a duct and out of the building. When that duct is restricted, usually by lint, the heat cannot escape and stays in the room instead. The dryers then hold their heat longer and run for more minutes per load, so the room keeps climbing through the day.
In most cases, yes. Clearing lint from the full duct run restores the airflow the dryers were designed to move, so heat and moisture leave the building rather than backing up indoors. Cycles also tend to finish faster once airflow is restored, which cuts the total heat poured into the room. If the room still runs hot after cleaning, the make-up air supply is usually worth checking too.
For a high-use commercial laundry, every six to twelve months is a common interval. Longer duct runs and those with several bends collect lint faster and may need cleaning more often. A cleaning report that records how heavily the duct had loaded is the best way to set the right interval for your specific room.
Phoenix Duct Clean · by the numbers
Phoenix surveys and cleans kitchen and building ductwork to the TR19 standard - measured, cleaned and certificated, UK-wide.