Steam looks like the obvious answer to sticky grease inside a kitchen extract system: it is hot, it is water, and most operators have used it successfully on a hob or a griddle. On ductwork the same tool can be the reason a clean fails. The inside of an extract run is a long, mostly horizontal cavity with limited access, a grease load that has polymerised over months, and a building structure that will carry every drop of run-off somewhere it was not intended to go. Before a wand goes anywhere near a duct, the questions below are the ones worth answering.
1. What does the duct actually contain, and how thick is it?
Two very different deposits sit in the same duct. Fresh grease from the day's service is soft and moves with warm water. Grease that has been baked on by repeated heating cycles has turned into a varnish-like film that water and detergent alone will barely shift, and that is the layer most operators want removed. Steam helps because heat softens the polymerised layer before pressure moves it, which is the same logic used for [kitchen exhaust duct grease cleaning](https://www.powerde.net/qingjiehangye/41.html) on hard-to-reach cooking surfaces.
The practical step before booking any equipment is a look inside. Access panels, fan housings and the first metre of horizontal run will tell you whether the deposit is soft, hard or layered, and roughly how deep it is. That single inspection decides whether the job needs dwell time and heat, chemical pretreatment, or mechanical scraping that steam will never replace. Guessing is what produces the complaint that steam "did nothing".
2. What access exists, and what does that rule out?
Steam is a contact method: the operator has to see and reach the surface. That is its limitation. Compare your duct against these conditions:
- How many access hatches exist, and how far apart are they? If a wand can only reach a short distance from each hatch, only that distance gets cleaned, whatever the machine is capable of.
- Is the run horizontal, and does it fall toward or away from the collection point? Water will follow the fall whether you plan for it or not.
- Are there bends, dampers, a fan casing or a fire damper in the section? Those parts trap liquid and can be damaged by direct spray.
- Is the duct shared with anything that must not get wet — electrical containment, luminaires, insulated ceilings, plasterboard soffit?
If the duct has long unbroken runs with only a couple of small hatches, no handheld method will clean the whole interior, and a plan that promises otherwise will end with wet ceilings and a duct that still has grease in it. Where access is genuinely poor, the right decision is to add access panels before cleaning, or to change the cleaning scope rather than the machine.
3. Where does the run-off go?
This is the question operators most often skip, and the one that causes the most expensive damage. Loose grease, hot water and detergent emulsion leave the duct as a liquid that has to be caught, contained and disposed of through a waste route that accepts grease. Check these points before starting:
Is there a drain, gully or grease interceptor below or near the duct? A kitchen's [central kitchen degreasing](https://www.powerde.net/qingjiehangye/41.html) waste belongs in the interceptor route, and duct run-off belongs there too. Run-off that goes into a rainwater drain or a prep-area sink moves the problem somewhere harder to deal with, and a blockage downstream costs more than the clean saved.
If there is no drain in the duct zone, decide in advance how the liquid will be collected — trays, dammed sections, absorbent granules, a vacuum unit rated for the job — and how many people it takes to do that. Collection is not an optional extra; it sets the water volume you can safely use.
4. Dry steam or wet steam, and why the mode matters
Inside a duct, water is the enemy and heat is the tool. A machine that generates only a saturated, wet jet will soak the duct and leave the run-off problem behind while doing comparatively little to baked-on film. A [dry and wet steam cleaner](https://www.powerde.net/qingjiehangye/41.html) lets the operator put most of the work into the drier mode — heat into the deposit, minimum free water — then use the wetter mode briefly as a rinse once the film has released.
Write down which mode is used for which part of the job before the shift starts, together with the dwell on the deposit, the working distance and the number of passes. Those three details are what make the method repeatable by a second operator, and they are usually what separates an adequate result from an inconsistent one.
If the site is evaluating a fixed unit, read the published specification rather than assuming. The [Fixed Steam Cleaning Machine PowerDe HW02](https://www.powerde.net/qingjiehangye/41.html) page lists a 220 V supply, a tap-water inlet, an 80 L tank and both dry and wet steam modes. Check the voltage available at the duct, whether a water connection is within reach of the work area, and whether hose length from the machine actually reaches the hatches you intend to work through. Also confirm the safety provisions listed on the page, including leakage, short-circuit, high-temperature, high-voltage and water-shortage protection, and make sure the crew knows that a machine tripping one of those protections has to be reported, not repeatedly reset during a shift.
5. What has to be protected inside and around the duct
Steam produces vapour, and vapour travels further than the jet. Anything sharing the ceiling void needs to be treated as part of the job: electrical containment and junction boxes, fan motors and their cabling, luminaires, insulation, and any gypsum or timber that will take on moisture. Cover or isolate those items, and protect the kitchen below as well — the space under the access hatches is where the run-off will land.
Fire dampers, dampers links and their actuators are a specific case. Direct spray into a damper mechanism can distort blades, jam linkage or wash out lubricant, and a damper that no longer closes correctly is a fire-protection failure discovered at the worst possible moment. Where dampers sit in the section being cleaned, either exclude them from the wet work or inspect and function-test them afterwards.
6. Fire risk: what steam does not remove
High-temperature steam is close to the ignition temperature of kitchen grease, and a duct that is heavily loaded is a hot surface in a building. Two consequences follow. First, cleaning a duct with a heavy deposit is not a routine housekeeping task to be improvised by whoever is free that afternoon — it needs a planned method, controlled water volume and someone watching the work area.
Second, if a section is thickly coated, the honest answer may be that steam is not the tool for that section. Deposits of that depth generally need to be scraped and removed mechanically, with the residue collected, and the duct then finished with a lower-volume method. Steam is most effective as recurring maintenance on extract that is cleaned often enough not to build deep film — which is the argument for a shorter interval with lighter work, rather than a long interval with heroic work.
7. Insurance, records and who signs it off
Before choosing the method, check what the building's insurance or fire policy requires for extract cleaning, and what standard your inspecting authority expects to see evidenced. Many policies and fire risk assessments are written around documented access, deposit depth and the parts of the system covered, not around the equipment used. If your method cannot produce a record of which sections were opened, what the deposit looked like, and what was removed, that method will not satisfy an audit however clean the reachable surfaces look.
Keep signed job sheets, before-and-after photographs through the access hatches, and interceptor emptying records in the same place. That file is what protects the operator and the site if the extract is ever questioned.
8. How to judge the result
Agree the acceptance check before work starts, in terms an operator can verify in seconds: bare metal visible through the access hatches in the sections treated, no loose or sliding grease, no standing water left in the run, the fan housing free of build-up, and the surrounding kitchen undamaged and dry. Then check function — the extract still pulls correctly, dampers still operate, and nothing downstream has been flooded.
Record how long the job took and how much water it used. Those two numbers tell you whether the chosen machine and access arrangement suit this building, and whether the next clean should be scheduled sooner with less work each time.
A short pre-start checklist for the operator
- Deposit inspected through access panels; depth and condition recorded.
- Reachable length from each hatch measured; uncleanable sections identified and reported rather than assumed.
- Run-off route defined, collection in place, interceptor checked before starting.
- Mode, dwell, distance and passes written down for the worst two surfaces.
- Dampers, electrical containment, luminaires and insulation protected or excluded.
- Power supply, water connection and hose reach confirmed at the actual work position.
- Acceptance criteria and sign-off name agreed before the work, not after.
Then test it on your own duct before committing to a machine
Duct geometry varies more between buildings than any equipment specification accounts for, so a trial on your own extract is worth more than a specification sheet. Shenzhen PowerDe Automation Precision Equipment publishes parameters for each machine in the [Cleaning Equipment Series](https://www.powerde.net/qingjiehangye/) and works with operators on site-specific requirements. Send photographs taken through your access hatches, the hatch layout and the deposit description through the [contact page](https://www.powerde.net/contact/) and ask for a configuration matched to that duct — including whether steam is the right method at all for the sections you cannot reach — rather than choosing from a catalogue.
