Anyone who has cleaned a commercial kitchen exhaust duct knows the sequence: access panels off, scrapers out, degreaser applied, agitation, rinse, and a floor that ends up wetter than the duct got. The reason ducts are so labour-intensive is not that grease is impossible to remove. It is that the duct is long, enclosed, overhead and full of stubborn, layered, part-cooked fat — and that removing it with large volumes of water leaves the operator cleaning up a second mess afterwards.
Steam handles this differently, because the same machine can be run in two modes that do different jobs. Dry steam and wet steam are not a marketing distinction; they are two operating points with different water loading, and choosing between them decides whether the job takes two passes or four. Before either mode is selected, the operator also has to solve the problem the title of this article implies: where the loosened grease goes.
Dry steam for breaking the bond, wet steam for flushing it
Dry steam carries little free water. It delivers heat into the grease film with minimal runoff, so the fat softens and separates from the metal surface without flooding the duct. That is what makes it useful on the first pass: heavy build-up on the inside of a duct, the fan housing, the baffle vanes of a grease filter, and the sticky carbonised film around the hood opening that scrapers smear instead of lifting.
Wet steam carries more water with it, so it transfers heat and adds flushing action at the same time. That suits the second pass, when the grease has already been heated and needs to be carried off the surface, and it suits flat open areas where the runoff can be directed into a pan or a drain. On a hard coat of old, layered build-up, wet steam alone tends to glaze the surface — the outer layer heats and slides, the layer beneath stays put, and the operator keeps working without progress. Dry steam alone leaves heated grease sitting on the surface with nothing to move it. The mode choice is therefore about sequence, not superiority.
The constraint that decides the method: you cannot hose a duct
A duct has no floor. Everything dislodged falls — into the hood, onto the cooking line, into the filter box, or back along the duct run towards the fan. Rinse water has nowhere to go but out of the access panel and down the wall. This is why high-volume pressure washing is the wrong tool inside ductwork, and why the low-water behaviour of steam is the actual reason to specify it here.
Ask any supplier for the water consumption of the machine at the mode you intend to use, and then plan the collection: drip trays and catch pans under every open panel, a squeegee and absorbent for the terminal run, and a clear answer on whether the machine's runoff can be contained at all. Fixed Steam Cleaning Machine PowerDe HW02 is specified with a 6 kW heating element on a 220 V supply, dry-steam and wet-steam mode selection, an 80 L SUS304 tank, and 0.8 MPa vapour pressure — and it also carries a vacuum function, which matters in exactly this kind of job where loosened residue has to be taken out rather than allowed to fall. Two warnings, though. The product page positions this machine around vehicle cleaning at fuelling and parking sites — exterior, interiors and engine compartments — not kitchen ductwork, so ask the manufacturer in writing whether it is appropriate for duct duty before treating that specification as a kitchen recommendation. And confirm the numbers themselves: the customer's own site shows inconsistent model naming around the 220 V fixed units, so get the exact model and its parameters in the quotation.
What to specify for kitchen exhaust duct cleaning
- Selectable dry and wet steam from one machine, with mode changeover that takes seconds rather than a shutdown and a tool.
- Enough steam temperature and pressure to heat thick build-up in a single pass. If the specification does not state temperature and pressure, request them.
- Electrical safety features named in writing: leakage, short-circuit, high-temperature, high-voltage and water-shortage protection. Confirm what the machine does when the tank empties mid-job.
- A supply arrangement that matches the site. A fixed unit needs a 220 V outlet and a route for the hose to reach the highest access panel; if the duct runs across several floors or outdoors, mobile units that run on dry steam, wet steam and hot water may fit the pattern better.
- Hose and wand lengths that reach, plus a nozzle set suited to flat plate and to corner joints. Underspecified reach is the most common reason a steam job fails on site.
- Consumables named and available: seals, hoses, guns, nozzles, and the water-inlet fitting. The customer's 220 V fixed units use a 4-point internal-tooth joint for tap-water inlet; check that against your plumbing.
Decide on a trial section, not on a brochure
Pick one duct section with representative build-up — usually the first metre past the hood, where the layer is thickest — and have the supplier demonstrate both modes on it. Record four numbers: passes needed to clear the layer, litres of water consumed, how long the surrounding equipment stays wet, and the labour time for the section including panel removal and cleanup. Those four figures, compared across two machines, answer the question better than any specification sheet.
Write the safety features, the mode definitions and the consumable terms into the order. A duct-cleaning machine is judged on how much of the job it lets one operator finish without flooding the kitchen underneath it.
