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Choosing Wet vs Dry Vacuums: Focus on Job, Not Motor Size
A procurement manager for a 240 room hotel in Antalya bought 40 extraction units in April on one specification line: 1600 W. By July, half the fleet could not dry a room carpet before the 14:00 check-in, and the property booked EUR 11,300 in downgrades. The motors were as advertised; sealed water lift was 1400 mm H2O on a machine needing 2200 mm to pull water out of a dense carpet backing. Wattage bought power. It did not buy recovery, and every wet room became a refund.
Two Numbers, Two Different Jobs
Sealed water lift, in mm H2O or inches of water, is the suction a machine develops with the hose blocked; it lifts water and overcomes carpet resistance in a 4 m hose. Airflow, in L/s or CFM, carries debris and moves that water into the tank. Performance is the product of both: air watts equal inches of lift times CFM over 8.5. That figure beats any motor rating, so ask for air watts on every quote.
Thresholds matter more than the formula. Upholstery needs about 1800 mm H2O and 30 L/s. Hotel corridor carpet needs 2200 to 2500 mm H2O at 45 to 55 L/s. A workshop vac is specified the other way round: 60 L/s and above, plus enough lift to hold a water column. A compact new household portable spot cleaner sits at the low end, a twin motor extractor at the top. Get the balance wrong and you own a machine that makes noise and leaves the water behind.
Peak Wattage Is a Marketing Number
The 1600 W on the box is input power at the wall, and on a universal motor it is the peak of a surge, not the continuous draw. What reaches the carpet is air watts, and the conversion is brutal: a 1600 W single motor extractor delivers 250 to 350 air watts, about 20 per cent of the box figure. Better fan geometry delivers more from the same input.
Motor architecture follows the job. A bypass motor cools itself with a separate cooling fan, so it survives the interruption when a float ball closes, and it is the only choice for wet pickup. A thru-flow motor is cooled by the working air: efficient on dry work, but blocking the hose cooks it. That is why every wet machine needs a float shutoff and a bypass motor, and why a thru-flow unit must never be quoted for flood recovery. Duty rating is the third filter: housekeeping runs 4 to 6 hours per shift, and a unit rated for 30 minute cycles trips its cutout by 10:00.
Tank Size, Shift Length and the Emptying Maths
Tank capacity is a labour specification, not a performance one. Hot water extraction applies roughly 15 to 20 litres per 100 m2 and recovers 75 to 85 per cent. Check emptying frequency against the shift, because a tank emptied every 12 minutes costs an operator more than the machine saves. Where volumes do not justify a full chassis, a tough two colour bucket series unit keeps crew cost sensible.
Dry time is the specification buyers feel. Over 20 per cent of applied solution left in the pile pushes drying past 6 hours; past 8 hours brings wicking and odour complaints. The variables are recovery rate and airflow, plus 22 C and 50 per cent RH. If the schedule needs a 4 hour turnaround between checkout and check-in, put it in the tender and ask for recovery in litres per minute, not tank size. An electric portable wet and dry spot cleaner for fabric is the right tool for a room attendant working traffic lanes; a full size extractor belongs on the corridor schedule.
Filtration and Noise for Occupied Buildings
Filtration is where a machine protects the motor or destroys it. Dry fine dust needs a cartridge or a HEPA H13 element to EN 1822, holding 99.95 per cent at the most penetrating size. A cloth bag is a pre-filter, not a filter, and it passes respirable silica straight through the motor. Wet pickup needs the cartridge out, a foam sleeve and a float shutoff, or the first tank of dirty water becomes a motor replacement.
Noise decides whether you can clean while the building is occupied. Measured at 1 m, a single motor extractor runs 72 to 78 dB(A) and a twin motor unit passes 80. For daytime corridor work hold 70 dB(A); for night work in guest areas, 60 dB(A). Under the EU framework, 80 dB(A) is the lower action value and 87 dB(A) the limit, so anything above 80 puts the operator into hearing protection. Insulated housings and a silencer buy 3 to 5 dB, the gap between day and night work.
The Spec Matrix to Send Your Supplier
Build one row per application and send the whole table with the enquiry.
- Hotel room carpet: 2200 mm H2O minimum, 45 L/s, 4 hour dry time, 20 L tank.
- Lobby and corridor: continuous duty above 4 hours, 70 dB(A) cap, 30 L tank, wheels.
- Upholstery and mattress: 1800 mm H2O, 25 to 30 L/s, hand tool under 1.2 kg, 8 L tank.
- Workshop flood and swarf: 60 L/s, bypass motor, float shutoff, 30 L or larger, oil resistant hose.
- Hard floor recovery: 50 L/s at 450 mm scrub width.
- Documentation: air watts, recovery rate in L/min, dB(A) at 1 m, EN 1822 filter grade.
The Bottom Line
Stop quoting motor wattage. Specify water lift, airflow and air watts, add recovery rate and dB(A), and match them to the room, the shift and the dry time. Machines built on that balance, such as a fabric sofa and carpet washing spot cleaner, do not come back as complaints. A machine that leaves water in the carpet is not a cleaning machine, it is a liability.