What the two modes actually do to the panel
Dry steam and wet steam are the same boiler working at two different water loads. Dry steam leaves the nozzle mostly as vapour: it carries heat into the bonded film of road grime, exhaust soot and light oil that clings to a hood or a door, and it loosens that film without flooding the panel. Wet steam carries more free water with it, so it does the mechanical work — lifting compacted grime off a wheel arch, a rocker panel or a bumper where the deposit has some thickness to it.
On a painted body the practical difference is dwell time and rinse. Dry steam lets an operator hold the nozzle moving over a horizontal panel and let the heat do the work, which suits a showroom-fresh or freshly waxed car where there is little loose dirt and the risk is marring the surface. Wet steam suits the lower halves of the vehicle, where dirt is abrasive and must be floated off rather than wiped off. Choosing between them is not a brand preference; it is a reading of what is on the panel.
PowerDe's fixed dry and wet steam cleaner is the model whose detail page is most explicit about this. It switches between the two modes on one machine and its specification lists 160° steam temperature, 0.8 MPa vapour pressure, 6 kW heating power and an 80 L SUS304 tank, with the cleaning modes recorded as dry steam and wet steam, with a vacuum cleaner added for the interior work. The page places it at service stations and parking lots, doing vehicle exteriors, interior vacuuming and disinfection, and engine-compartment cleaning.
Check the site before you choose a mode
On forecourt and car-park bays the constraint is usually supply, not the machine. A fixed unit needs three things on site: a 220 V supply that matches the machine's working voltage, a tap-water inlet the machine can accept, and a surface that can get wet. The HW02 records a tap-water inlet with a 4-point internal-tooth joint (1/2 inch) and dimensions of 1,200 × 800 × 1,200 mm including handles, so it occupies a fixed position rather than moving around a bay.
Where the pitch has no water point, no mains supply, or the bays are too tight to manoeuvre a fixed unit into, a mobile unit changes the answer. The driving style steam cleaner models in the same range add a hot-water mode on top of dry and wet steam, run from a 48 V battery, and are listed for indoor garages and the narrow spaces of outdoor parking areas. That battery supply is what makes the process possible in an underground bay with no socket near the car.
Driveway drainage decides more than it looks. Wet steam and hot water put volume on the ground; dry steam does not. On an indoor epoxy floor, in a basement bay, or anywhere run-off has to be swept or squeegeed away, a dry-steam pass with a microfibre follow-up keeps the floor usable between cars. On an outdoor bay with a gully, the same job is faster with wet steam. Set the mode by the floor as well as by the car.
Confirm the power supply and the water supply in writing before the order is placed. A machine that will not run at its rated pressure on an installation's supply will not deliver the results the data sheet promises, and that conversation is much cheaper before the unit is delivered than after.
How the two modes are used on the bodywork
Work the vehicle in the same order every time, and the mode choice stops being a debate. Start with the sections that carry the heaviest deposit — wheels, arches, sills, lower doors — where wet steam does the work, then move up to the horizontal panels and glazing, where dry steam finishes. Rinse or wipe as you go rather than letting loosened grime dry back onto the paint.
Two handling habits matter more than the mode on a painted surface. Keep the nozzle moving and keep it off the paint: a stationary jet concentrating heat on one spot of a panel, or a nozzle pressed into the surface, is how swirl marks and heat marks get introduced on a job that the machine was perfectly capable of doing well. Use the fan or lance nozzle the supplier supplies rather than improvising an adapter, and let the heat and the pressure do the work instead of the operator's hand pressure.
Trims, badges, decals and older clear coats are the exception cases. Where a wrap, a decal edge or a repaired panel is present, test on an inconspicuous area first and use dry steam with a shorter dwell. Plastic exterior trims, headlight lenses and rubber seals should be treated as their own question rather than lumped in with the body panels — a wrap or a replacement seal quoted after a steam job is a cost that turns a good review into a dispute.
A short rule that survives contact with real cars: wet steam below the beltline, dry steam above it, and a test patch on anything that has been repaired, wrapped or repainted. It is not a universal setting, but it is a defensible default an operator can be trained on in one shift.
Engine bays and interiors are separate decisions
Exterior mode choice says nothing about the engine bay, and buyers routinely get this wrong when they specify a single machine for a whole service. An engine compartment is a dry-steam job: the heat lifts oil and brake dust off the block and the plastic covers, and the low water volume matters because the bay cannot be flooded. The HW02's own description places engine-compartment cleaning on the same machine as the exterior work, which is why the mode switch matters on a forecourt unit rather than being a nice extra.
Interiors are a third case again. Seats, carpets and floor mats need extraction, not steam alone, and the fixed unit's specification records the cleaning modes as dry steam and wet steam with a vacuum cleaner, which is what allows one machine to handle the interior pass as well as the exterior. Steam on a seat upholstery is a finish, not a substitute for extraction on a wet carpet.
When you request a quotation, ask the supplier to confirm in writing which modes the machine covers, which of the three jobs — exterior, interior, engine bay — the machine is being offered for, and which accessories come with it. A specification that lists one machine against all three jobs is worth a second read.
Reading the specification against the job
For exterior work, four figures on the data sheet decide how the machine behaves at the panel. Working pressure is what lifts the deposit, so compare the rated vapour pressure against what the gauge shows at the nozzle under load, not only at the machine — a long hose, a partly blocked wand or a worn nozzle all eat pressure between the two points. Steam temperature and heating power together determine how fast the machine recovers between cars, which is the figure that decides whether a busy Saturday is sustainable. Tank volume sets how long a bay can run before the operator stops to refill.
Ask for those figures for the specific model, in writing, and check them against your supply before ordering. Where several models look similar, the differentiators that actually change a forecourt workflow are the mode set (dry and wet steam, or dry and wet steam plus hot water), whether the machine is mains-powered or battery-powered, and how it moves — hand-pushed, or driven.
Safety items belong in the same review, because they are the parts that keep a pressurised, mains-powered machine safe in a public forecourt. The HW02 page lists leakage, short-circuit, high-temperature, high-voltage, water-shortage and high-voltage-explosion protection. Put each protection on a planned test schedule and record the test; a protection that has never been checked is an assumption, not a control.
Run a side-by-side test before you buy
The cheapest way to settle the dry-versus-wet question for your own yard is to test it on your own dirt. Pick two vehicles that represent the worst of what you actually wash — a city car with road film on the bodywork, and one with wheel arches that have not been touched in a month. Set the mode for each section on a written task card, note the pressure the operator should see on the gauge, and time the job.
Record four things: minutes per vehicle, water used, whether the floor was usable again between cars, and whether any trim or repair came back damaged. That short record turns a specification argument into a comparison you can act on, and it gives your supplier something concrete to respond to when you ask which model fits the bay.
Put the same decision on paper for the operators. One page that states, for each job type, which mode to run, what pressure they should see on the gauge, and what to do when the reading drops below it. Machines rarely lose the argument about dry versus wet steam; undocumented workflows win it, and the cost shows up later as longer cycles, re-washes and a pressure fault report that turns out to be a closed inlet valve.
If your site needs a mode set, a power arrangement or a water connection that the standard pages do not describe, send the layout of the bay, the supply you have and the vehicle mix you wash, and ask the supplier to confirm the model, the pressure, the temperature and the heating power for that installation before you order.
