Commercial dishwasher types and how to pick the right one

Warewashing is the part of a kitchen fitout that gets specified last and causes the most trouble afterward. A machine that cannot keep up turns into a pile of dirty crates by 8pm, and the fix is almost never cheap once the room is built.

Get the throughput calculation right and most of the other decisions follow.

Racks per hour, at peak

A standard dish rack is 500 by 500mm. It holds roughly 25 glasses, or 18 dinner plates, or a mixed load of cutlery and crockery from about 8 covers.

So a restaurant doing 120 covers across a two hour dinner service generates around 15 racks of crockery, plus glassware, plus kitchen pans. Call it 25 racks in two hours, or about 13 racks per hour.

But that demand is not even. Most of it arrives in a 40 minute window as tables turn. Your real peak might be 25 racks per hour even though your average is 13.

Size for the peak. The machine sitting idle between rushes costs you nothing. The machine falling behind during the rush costs you a section of your kitchen.

The four types

Undercounter. Fits under a 900mm bench, takes one rack, cycles in 60 to 180 seconds. Up to about 30 racks an hour in practice. Right for cafes, small bars, and as a dedicated glasswasher at a service bar.

Passthrough or hood type. The hood lifts, a rack slides in from one bench and out to another. 40 to 60 racks an hour. This is the default for most restaurants and pubs. It needs a dedicated dish area with an in bench and an out bench, so allow around 2.5 metres of linear space minimum.

Rack conveyor. Racks travel through on a chain past wash and rinse zones. 100 to 250 racks an hour. For large venues, function centres, hospitals and aged care. Needs a purpose designed room.

Flight type. No racks. Crockery stands on pegs on a continuous belt. 5,000 plus plates an hour. Stadiums, universities, large institutional kitchens.

Most operators reading this want an undercounter or a passthrough, and the decision between them is usually about whether you have the bench space and the drainage for a hood machine.

Hot water is the hidden constraint

This is the number one commercial dishwashers install problem.

A machine needs incoming water at a specified temperature, usually 55 to 60 degrees for a standard model. It heats that to 82 degrees for the sanitising rinse using an internal booster.

If your incoming water is cold, the booster has to do all the work, the cycle stretches, and throughput collapses. If your hot water system cannot sustain the flow, you get a hot first rack and progressively cooler ones after that.

Work out your hot water demand before ordering, including everything else in the kitchen drawing at the same time. A 50 litre undersink unit will not support a passthrough machine during service.

There are cold fill machines with larger internal boosters, which suit sites where running a hot line is impractical. They draw considerably more power, so check your board has the capacity.

Sanitising: thermal or chemical

Thermal machines rinse at 82 to 85 degrees, which sanitises by heat alone. Standard in Australia, no chemical sanitiser needed in the rinse, and it produces dry ware because the hot crockery flashes off the remaining moisture.

Chemical machines rinse cooler and use a sanitiser dose instead. Lower power draw, lower running temperature, but ware comes out wet and needs air drying, and you have an ongoing chemical cost.

For most Australian commercial kitchens, thermal is the right call. Food safety auditors are familiar with it and a rinse thermometer or data logger makes compliance straightforward.

Ask whether the machine logs final rinse temperature. Being able to show an auditor a record rather than an assurance is worth having.

Water and chemical consumption

Modern machines use 2 to 3 litres per rack. Older ones use 5 to 8.

At 200 racks a day, the difference between a 2.5 litre machine and a 6 litre machine is 700 litres a day, which is both water cost and the energy to heat it. Over a year that gap is substantial, usually more than the price difference between the machines.

Detergent and rinse aid dosing should be automatic and adjustable. Manual dosing wastes chemical and produces inconsistent results. Check the dosing pumps are serviceable and that the pickup tubes can be moved between drum sizes.

Ask your dishwasher detergent supplier to set the dose against your actual water hardness. A dose set for soft water in a hard water area leaves film on glassware, and the usual response is to increase rinse aid, which makes it worse.

Installation details that matter

Drainage. Most machines gravity drain, which means the waste point must be below the machine outlet. In a slab on ground kitchen without a suitable floor waste you may need a drain pump, which is an extra failure point.

Ventilation. A passthrough machine releases a large cloud of steam when the hood lifts. Without a condensing hood or extraction above it, that steam goes into the ceiling and eventually into the plasterboard. Budget for it.

Power. Thermal machines with boosters commonly need three phase. Confirm what is available at the site before you order, because a single phase to three phase upgrade is a serious cost.

Levelling. Machines must sit level for the wash arms to work evenly and for the tank to drain. On a kitchen floor with a fall to the waste, adjustable feet are not optional.

Glasswashers are a separate question

If you run a bar, a dedicated glasswasher is worth having alongside the main machine. Glass needs a gentler wash, a lower temperature and different chemistry to avoid etching and clouding, and mixing glassware in with greasy crockery ruins both.

A small undercounter glasswasher at the service bar also keeps glasses out of the dish pit entirely, which speeds up the bar and reduces breakage in transit.