Estimates for cleaning kitchen exhaust ducts usually go wrong for the same reason twice in one year: somebody is asked how long the job will take, a round number is given, and the crew arrives to find a deposit three times thicker than anyone expected. A defensible estimate does not come from a rule of thumb copied off a forum. It comes from a short list of variables you can measure, a written method for each duct section, and a duration assigned to every task in the sequence. The steps below are the ones a facilities team can apply with a tape measure, a inspection camera if you have one, and the site's own maintenance records.
1. Start from the duct layout, not from the number of hoods
Pull the extract drawings or walk the run with a tape. For each section record the internal size, the length, whether the duct is accessible from inside or only from access hatches, and how many bends, dampers, fans and terminations sit on that run. A single restaurant hood may feed a short horizontal stub and two floors of riser; a central kitchen may feed a shared trunk with six branch takes. Time follows the number of separate sections and the number of access points, not the number of hoods in the kitchen. Write the run as a list of named sections before estimating anything, because a duration you cannot attach to a named section cannot be checked later.
2. Grade the deposit instead of guessing at it
Open an access hatch on one horizontal section and on one riser, photograph what you find, and grade what you see on a simple three-step scale: a thin film that a cloth removes; a soft, sticky build-up with a visible texture; or a hard, varnished layer with drips forming on the underside. Grading matters because the third category needs heat applied before any mechanical work, and heat adds dwell time that no scraper-only method can avoid. Where the site keeps previous cleaning records, use them to fix the grade rather than the interval, since a kitchen that runs a grill line builds deposit far faster than one running steamed and boiled product on the same hood count.
3. Choose the method per section and time the worst one
For light and medium build-up, manual scraping and a degreasing detergent that is left to act is usually the short path. For baked-on grease, hot water and high-temperature steam do the work that solvent and elbow grease only slow down: heat softens the polymerised layer, pressure lifts it, and the surface is left closer to clean than a wiped surface. For that class of job a fixed unit such as the PowerDe HW02 steam cleaner suits a kitchen with a water supply and a wash point near the extract line, while a mobile unit from the PowerDe cleaning equipment range suits sites where one crew covers several servery areas. State the mode in the plan: the drier steam mode puts heat into a hard deposit, the wetter mode finishes the surface. Then time one representative section with the crew actually doing the job, and use that measured rate for the remaining sections of the same grade.
4. Break the job into tasks and add the time nobody books
Estimate the sequence, not the cleaning alone. The usual line items are: isolating the fan and lighting, laying protection and setting up containment under the access points, opening hatches, applying heat or chemical and letting it dwell, removing the deposit, wiping and rinsing the accessible interior, cleaning the hood panels, filters and the fan housing, clearing the run-off, closing up, and re-testing the extract. Add the hatch work separately, because a run with ten small hatches takes far longer than a duct you can walk inside. Then add a fixed allowance for the two items crews forget: the time to move equipment between floors and the time to clean up between sections so that run-off does not cross a food area. Those two items are where a stated six-hour job quietly becomes nine.
5. Put water, run-off and drainage into the estimate
Water volume and the route it takes change the duration more than any other variable. Greasy run-off from kitchen exhaust duct grease cleaning has to reach a waste route through the grease interceptor, not a prep-area sink or an open surface drain, so the plan must name the collection point, the trays or vacuum recovery used, and who empties them. A site with a nearby tap and a gully collects and disposes of run-off in minutes; a site three floors up without services needs containers carried by hand, and that alone can add an hour or more to the day. Record the water source next to each section, and let it decide whether a fixed or a mobile machine is the right tool.
6. Book the people and the windows, then sanity-check the total
Convert the task list into crew-hours with named owners and rough durations per section, then test the total against the operating windows you actually have. Kitchen extract work is usually done outside service hours, which means an eight-hour estimate can occupy two nights. That is fine, but the estimate has to say so, because the fan isolation, the fire risk assessment and the kitchen's production plan all depend on knowing which nights are lost. A simple check works: multiply the measured rate for the worst graded section by the number of sections of that grade, add the forgotten allowances from step four, and compare the result with the number given by whoever last cleaned the site. If the two figures differ by more than about a third, one of them is wrong, and the difference is worth resolving before you commit the date to the kitchen manager.
7. Record the estimate and the result, then re-use both
Keep the section list, the deposit grade, the method, the crew size and the actual hours in one sheet, signed off on completion. That sheet is the basis of the next estimate, and it is also evidence for the fire risk assessment, since deep grease build-up in extract lines is a fire issue as much as a hygiene one. After two cycles you have a site-specific rate that no outside contractor can argue with, and a schedule you can shorten or extend on facts. Where the ductwork is unusual — a long servery run, a shared trunk serving several operators, a riser with no internal access — the machine and the method are worth specifying against the site rather than bought from a catalogue. Shenzhen PowerDe Automation Precision Equipment publishes parameters for each machine in its cleaning range, and customized cleaning equipment can be specified against your duct layout and cleaning cycle; send the section list and photographs of the worst deposits through the contact page and ask for a configuration matched to the job.
