A commercial dishwasher pumps out enormous amounts of heat and moisture. Every cycle generates a cloud of steam, and if that steam has nowhere to go, it saturates the air, condenses on every cold surface, and turns the area into a tropical greenhouse. The solution isn’t complicated, but it does need to be engineered properly.

Our engineers see this fault regularly across Shoreditch. A commercial AC installation contract catches this kind of issue early, well before it escalates into a costly PPM.

Missing or Inadequate Extract Ventilation

This is the root cause in most cases. The dishwasher area either has no dedicated extract hood at all, or the extract that’s fitted is undersized for the output of the machine. A commercial passthrough or rack-type dishwasher can generate 15–25 kW of heat rejection and litres of moisture per hour. A small domestic-style extract fan is not going to cut it.

The solution is a properly designed extract canopy positioned directly above the dishwasher, ducted to outside. The extract rate needs to match the steam output of the machine. For a passthrough dishwasher, we’re typically looking at 500–800 litres per second of extract, depending on the model and cycle frequency.

No Make-Up Air Supply

Here’s where a lot of kitchen ventilation goes wrong. You can install a powerful extract fan, but if there’s no make-up air supply to replace what’s being extracted, the system fights against a negative pressure in the room. Doors get hard to open, the extract fan can’t pull its rated volume, and you end up with the same problem — heat and moisture trapped inside.

Building Regulations Part F requires balanced ventilation in commercial kitchens. That means the air being extracted needs to be replaced with tempered fresh air — either through a dedicated supply fan or a supply air unit that conditions the incoming air. Without this balance, the extract system underperforms and the environment stays unbearable.

Broken Extract Canopy Fan

Sometimes the ventilation system is there but it’s simply not working. We’ve walked into kitchens where the extract fan had failed weeks ago and nobody noticed because the kitchen was already warm. Belt-driven extract fans need periodic maintenance — belts stretch, bearings seize, and motors burn out. If the fan isn’t spinning, the canopy is just a steel box hanging from the ceiling doing nothing.

Check the fan. Go outside and look at the discharge point. If you can’t feel airflow when the system should be running, the fan has likely failed. A replacement motor or fan unit is usually a straightforward swap.

Dishwasher Door Opened Mid-Cycle

Staff habits play a role here too. When the dishwasher door is opened before the cycle has completed — or immediately after the final rinse — a massive plume of steam escapes directly into the room. Modern commercial dishwashers have a condensation or drying phase designed to capture that steam before the door opens. If staff are overriding the cycle or yanking the door open early to speed up service, they’re dumping the entire steam load into the room.

Training helps, but it’s not a complete fix. The ventilation system still needs to cope with the heat and moisture that escapes during normal operation. Relying on staff discipline alone will always fall short during a busy service.

Dedicated Extract with Steam Condensate Management

For a proper long-term solution, the dishwasher area needs a dedicated extract system designed for high-moisture environments. This means stainless steel ductwork (not galvanised — it corrodes), condensate drains at low points in the duct run, and grease-free filters designed for steam rather than cooking grease.

The extract canopy should have a condensate gutter that drains captured moisture away rather than letting it drip back into the room. We’ve seen poorly designed systems where condensation runs back down the duct and drips from the canopy — making the problem worse, not better.

We have written a separate guide on commercial kitchens running too hot which covers a related failure mode worth checking. Similarly, our article on kitchen extraction not pulling properly explains another common cause of the same underlying issue.

Adding a Split AC Unit to the Wash-Up Area

In some kitchens, even with good extract ventilation, the dishwasher area remains uncomfortably warm because of radiant heat from the machine and residual ambient temperature. A small wall-mounted split AC unit can take the edge off, bringing the temperature down from unbearable to manageable.

It’s not a substitute for proper extract ventilation — the moisture still needs to go somewhere — but as a supplementary measure it can make a significant difference to working conditions. Position it so it’s not blowing directly onto the dishwasher or into the steam plume, otherwise you’ll just get condensation on the AC unit itself.

Getting It Fixed Properly

A hot, humid wash-up area isn’t just uncomfortable — it’s a food safety and staff welfare issue. Condensation dripping from ceilings onto clean crockery is a hygiene failure. Staff working in extreme heat is a health risk. Environmental health officers do flag these conditions during inspections.

ADK designs and installs kitchen extract ventilation systems across London — sized for the actual equipment, compliant with Part F, and built to handle the steam and heat that commercial dishwashers throw out. If your wash-up area is unbearable, call us and we’ll survey the space, specify the right system, and get it installed. No more dripping ceilings.

The post Commercial Dishwasher Area Too Hot and Humid — How to Fix It first appeared on ADK Kooling.

We found the grease filters so clogged they were effectively solid sheets of carbonised fat. Behind them, the ductwork was coated in a thick layer of grease buildup. The extract fan motor was still running, but it was trying to pull air through a system that had the resistance of a brick wall. The kitchen had become a pressure cooker with no exhaust.

This is one of the most common callouts we attend across Kings Cross. If your system has not been serviced recently, booking a PPM visit can often resolve the underlying cause before a full breakdown occurs.

Kitchen extraction failures are a health risk, a fire risk, and — if the Environmental Health Officer walks in — a business risk. Here’s what actually goes wrong and how to fix it.

Blocked Grease Filters — The One We See Every Time

Grease filters sit inside the canopy hood and catch airborne grease before it enters the ductwork. In a commercial kitchen producing any volume of fried or grilled food, these filters need cleaning weekly. Not monthly. Not “when they look bad.” Weekly.

Baffle-type stainless steel filters can go through a commercial dishwasher. Mesh filters need soaking in a degreasing solution. When this maintenance gets skipped — and in busy kitchens it always gets skipped eventually — the filters become a solid barrier. Airflow drops, the kitchen fills with smoke and steam, and the extract fan works overtime pulling against the blockage. That overwork kills the motor faster.

If your extraction feels weak, check the filters first. Nine times out of ten, that’s the problem.

Failed Extract Fan Motor

The extract fan is usually mounted on the roof or externally on the building wall. It runs for every hour the kitchen is operational — often 14-16 hours a day in a restaurant. Motors have a finite life, and in grease-laden environments that life is shorter than the manufacturer’s data sheet suggests.

Signs of a failing motor: reduced extraction even with clean filters, unusual humming or buzzing from the fan, the motor casing hot to the touch, or a tripped circuit breaker that keeps tripping when you reset it. A completely dead motor is obvious — no airflow at all and silence where there should be a constant hum from the roof.

Motor replacement is straightforward but needs to be correctly sized for the ductwork and kitchen volume. We carry common motor sizes and can usually replace same-day for standard installations.

Belt-Driven Fan With a Snapped or Slipped Belt

Larger kitchen extract systems often use belt-driven centrifugal fans rather than direct-drive motors. The fan impeller is connected to the motor via a V-belt. These belts wear, stretch, crack, and eventually snap. A slipping belt gives you reduced extraction with a squealing noise. A snapped belt gives you zero extraction with the motor still audibly running — confusing if you don’t know the system is belt-driven.

Belt condition should be checked at every service visit. A spare belt kept on site is cheap insurance — a few pounds for the belt versus lost revenue from a kitchen shutdown.

Make-Up Air Imbalance

This is the one most people miss. An extract system removes air from the kitchen. That air has to be replaced from somewhere. If the kitchen is sealed — doors closed, no supply air system, windows shut — the extract fan is trying to create a vacuum. It can’t. Extraction drops dramatically, and you get back-draughting through any available opening, including flues from gas appliances, which is genuinely dangerous.

If you are also experiencing commercial kitchens running too hot, the two faults may share a common cause. Our engineers frequently find that addressing one resolves the other. You might also want to read our guide on dishwasher areas running too hot and humid for additional troubleshooting steps.

Proper kitchen ventilation requires a balanced system: extract air out, supply air in. The supply air should be tempered (heated or cooled) so you’re not dumping freezing outside air into the kitchen in January. Many older kitchens were fitted with extract-only systems and never had adequate make-up air provision. If your extraction was always marginal, this is probably why.

Grease Buildup in Ductwork and Canopy

Even with properly maintained grease filters, some grease gets past and accumulates inside the ductwork over months and years. This narrows the effective duct diameter, increases resistance, and reduces airflow. It’s also a significant fire hazard — duct fires in commercial kitchens are more common than most operators realise.

Under DW/172 (the BESA specification for kitchen ventilation cleaning), extract ductwork should be cleaned at regular intervals depending on usage. Heavy-use kitchens — takeaways, restaurants cooking with solid fuel or high-volume frying — need cleaning every 3-6 months. Moderate-use kitchens every 6-12 months. The cleaning should be done by a specialist duct cleaning contractor, with before-and-after photographic evidence and a certificate of compliance.

Insurance companies are increasingly asking for DW/172 compliance documentation. If your ductwork hasn’t been cleaned and there’s a fire, your insurer has grounds to dispute the claim.

What to Check Before Calling

• Are the grease filters clean? Pull one out and hold it up to the light — if you can’t see through it, that’s your problem
• Is the extract fan running? Go outside or up to the roof and listen
• Is there a supply air system, and is it working?
• Has anything changed recently — new equipment, blocked vents, sealed-off openings?
• When was the ductwork last cleaned?

Kitchen Extraction Problems? Call ADK

A kitchen without proper extraction can’t operate. We diagnose and repair extract fan systems, replace motors, rebalance supply and extract airflow, and work with duct cleaning contractors to bring systems back to DW/172 compliance. Call 020 3974 1419 — we cover London and respond to urgent kitchen ventilation failures 24/7.

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