How to Choose a Commercial Dishwasher for Your Kitchen Size: The Complete UK Guide (2026)
Choosing a commercial dishwasher is really a throughput calculation: how many racks per hour must you wash through your busiest service, and which machine class delivers that without a pile-up at the pass? The four classes scale with kitchen size — a glasswasher for a bar, an undercounter for a small café or gastropub, a hood-type (pass-through) for a busy restaurant, and a conveyor/rack machine for high-volume or institutional kitchens. But the machine is only half the decision: the 82°C rinse that sanitises, the WRAS-compliant plumbing and backflow protection, the drainage and (often) three-phase supply, and — the one that quietly wrecks machines in hard-water areas — a water softener to stop limescale. This guide sizes the machine to your covers, then covers the installation and running costs so the dishwasher you buy actually lasts.
- Size by racks/hour, not covers alone: estimate peak racks per hour (covers × items per cover ÷ rack capacity ÷ peak duration), then pick a class whose rated throughput comfortably exceeds it.
- Four classes by kitchen size: glasswasher (bar/glass), undercounter (café, gastropub, ~small covers), hood/pass-through (busy restaurant), conveyor/rack-transport (high-volume, institutional).
- 82°C rinse sanitises: commercial machines finish with a hot rinse — the recognised benchmark is a final rinse around 82°C to sanitise and dry crockery. This is the hygiene reliability a two-sink hand-wash cannot match at volume.
- Cycle times scale with class: glasswashers and undercounters run ~1–3 minute cycles; hood machines ~1–2 minutes but load faster with racks pre-staged; conveyors wash continuously at high rack rates.
- WRAS & backflow protection: plumbing must protect the mains from back-siphonage — use WRAS-approved fittings and the correct air gap/backflow device. This is a legal and water-authority requirement, not optional.
- Water softener in hard-water areas: limescale is the number-one killer of commercial dishwashers. In hard-water regions fit a water softener or the machine furs up, wash quality drops, and boiler elements fail early.
- Installation matters: hot/cold feed, adequate drainage, and often a three-phase supply for hood and conveyor machines. Get the supply and drainage confirmed before you order.
- Service contract pays back: a dishwasher down at peak is a service-stopper. A planned service contract, descaling and fast breakdown response keep it running — factor it into the total cost.
Buyers usually shop dishwashers on price and rack size, then discover the machine can’t keep up at peak, the limescale has furred the boiler within a year, or the plumbing never got backflow protection and the water authority flags it. This guide is for the trade buyer sizing warewashing for a real kitchen — cafés, gastropubs, restaurants, hotels, care homes, contract catering, and function venues. It sizes the machine to your throughput and then covers the installation and running realities that decide whether it lasts. Craven Cooling stocks and sources commercial dishwashers, glasswashers, hood-type and pass-through machines to specification — browse the full Craven Cooling range or talk to us about your kitchen.
Table of Contents
- Decision 1: Sizing by Racks per Hour
- Decision 2: The Four Machine Classes by Kitchen Size
- Decision 3: Wash Cycles and the 82°C Rinse
- Decision 4: Water, Energy and Chemical Cost
- Decision 5: Installation — WRAS, Drainage, 3-Phase, Softener
- Decision 6: Service Contracts and Whole-Life Cost
- Dishwashers We Stock or Source
- Worked Example: Sizing for a Gastropub
- Dishwasher Buying Checklist
- Frequently Asked Questions
- Related Buying Guides
Decision 1: Sizing by Racks per Hour
The single number that sizes a dishwasher is racks per hour at peak. Everything else — machine class, cycle time, boiler power — follows from it. Undersize it and dirty crockery piles up at the pass mid-service; oversize it and you overpay on purchase, water and energy for capacity you never use.
Work out your peak racks-per-hour like this: take your busiest service’s covers, multiply by the items each cover generates (plates, glasses, cutlery, cups), divide by how many items a standard rack holds, then divide by the number of hours your peak wash-up runs. That gives the racks you must push through per hour — and the machine’s rated throughput must comfortably exceed it, because rated figures are laboratory-ideal and real kitchens load slower.
Match that ~10 racks/hour figure to the machine classes below. It sits comfortably in undercounter/hood territory for a gastropub of that size, whereas a 200-cover hotel restaurant or a school pushing hundreds of covers in a short lunch window needs a hood or conveyor machine rated for far more. Always buy headroom: a machine running flat-out at 100% of its rating all service will struggle, whereas one at 60–70% duty keeps pace and lasts.
Decision 2: The Four Machine Classes by Kitchen Size
Commercial warewashing scales in four classes, each suiting a kitchen size and throughput band. Choosing the class is mostly a function of the racks-per-hour figure you just calculated.
Glasswasher
Bar / glass — we stock or source- Dedicated to glassware, gentle wash
- Fast ~1–3 min cycles, undercounter
- Best for: bars, cafés, front-of-house
- Keeps glasses off the crockery machine
Undercounter Dishwasher
Small kitchens — we stock or source- Fits under a counter, single rack
- ~1–3 min cycles, plates + cutlery
- Best for: cafés, small gastropubs
- Low throughput, low footprint
Hood / Pass-Through
Busy restaurants — we stock or source- Lift-hood, racks slide in on tabling
- Higher throughput, in/out flow
- Best for: busy restaurants, hotels
- Often needs three-phase supply
Conveyor / Rack-Transport
High volume — we stock or source- Racks travel through continuously
- Highest throughput, institutional
- Best for: schools, large hotels, canteens
- Three-phase, dedicated wash area
| Class | Typical kitchen | Indicative throughput | Supply |
|---|---|---|---|
| Glasswasher | Bar, café front-of-house | Glass-focused, high cycle count | 13A / single-phase |
| Undercounter | Café, small gastropub | Low–moderate racks/hour | 13A / single-phase |
| Hood / pass-through | Busy restaurant, hotel | Moderate–high racks/hour | Often three-phase |
| Conveyor / rack-transport | School, canteen, large hotel | Very high, continuous | Three-phase, fixed |
Decision 3: Wash Cycles and the 82°C Rinse
How a commercial dishwasher cleans — and how it sanitises — is different from a domestic machine, and it is the reason a machine outperforms a hand-wash sink at volume.
A commercial cycle is fast and hot: a wash phase recirculates hot detergent solution over the load, then a final hot rinse both clears the detergent and sanitises. The recognised benchmark for that final rinse is around 82°C — hot enough to sanitise the crockery and to flash-dry it as the water evaporates off the hot surface. That combination of heat and speed is what a two-sink hand-wash cannot reliably match through a busy service: consistent, high-temperature sanitising on every rack, cycle after cycle.
| Class | Typical cycle | Sanitising | Throughput style |
|---|---|---|---|
| Glasswasher | ~1–3 min | Hot rinse (~82°C benchmark) | Batch, high cycle count |
| Undercounter | ~1–3 min | Hot rinse (~82°C benchmark) | Batch, single rack |
| Hood / pass-through | ~1–2 min | Hot rinse (~82°C benchmark) | Batch, racks pre-staged on tabling |
| Conveyor | Continuous | Hot rinse zone | Continuous rack transport |
Decision 4: Water, Energy and Chemical Cost
Three running costs sit behind every rack: the water it uses, the energy to heat that water, and the detergent and rinse-aid it consumes. Over a machine’s life these dwarf the purchase price, so size them into the decision.
Water: each cycle uses a defined volume of fresh rinse water — modern machines are far more frugal than older ones, but at hundreds of cycles a week the water bill is real. Energy: heating the wash tank and the rinse boiler is where the kilowatt-hours go; at £0.27/kWh a busy machine running all day is a meaningful line. Chemicals: commercial detergent and rinse aid are dosed automatically — the cost per rack is small but constant. Add them up per rack and multiply by your weekly racks to see the true per-week running cost.
These figures are illustrative — the exact numbers depend on the specific machine, your water and energy tariffs, and your rack volume. The point is to model it: a machine that is cheap to buy but thirsty to run can cost more over three years than a frugal one that costs more up front. Ask for the machine’s water-per-cycle and energy figures and cost them against your realistic weekly rack count.
Decision 5: Installation — WRAS, Drainage, 3-Phase, Softener
More dishwashers are ruined by bad installation than by bad manufacturing. Get these five installation points right before you order, not after.
The connection to the mains must prevent contaminated water siphoning back into the supply. Use WRAS-approved fittings and the correct air gap or backflow device for the machine’s fluid category. This is a water-authority requirement — get it done by a competent plumber and keep the paperwork.
The machine needs a drain that can take the discharge volume without backing up — often a gravity drain at the right height, or a drain pump for machines below the drain line. A poorly-drained machine leaves dirty water in the tank and floods the wash area. Confirm the drainage layout before install.
Glasswashers and undercounters usually run single-phase, but hood, pass-through and conveyor machines frequently need a three-phase supply to power their larger boilers. Confirm what the machine needs and whether your kitchen has (or can get) three-phase before you commit — retro-fitting three-phase is expensive.
Check your local water hardness. In a hard-water area, fit a water softener or ensure the machine’s built-in softener is correctly regenerated with salt — otherwise limescale furs the boiler and wash arms, wash quality drops, and the boiler element fails early. This is the single most cost-effective thing you can do for machine life.
Many machines take a hot feed to reduce the boiler’s heating load; confirm what the machine expects. Hood and pass-through machines release steam on hood-lift, so the wash area needs adequate ventilation. Plan the feed and the steam extraction as part of the install, not an afterthought.
Decision 6: Service Contracts and Whole-Life Cost
A dishwasher is a service-critical machine: when it stops mid-service, so does the pass. That makes maintenance and breakdown response part of the buying decision, not an afterthought.
A planned service contract covers scheduled maintenance — descaling, checking wash arms and jets, testing the rinse temperature and dosing — plus a priority breakdown response so a failure doesn’t shut you down for days. In hard-water areas the descaling alone justifies it. When you weigh up machines, weigh up the whole-life cost: purchase, install (plumbing, three-phase, softener), running cost (water, energy, chemicals), and servicing. The cheapest machine to buy is rarely the cheapest to own.
| Cost line | What it covers | Why it matters |
|---|---|---|
| Purchase | The machine, right class and throughput | One-off; the smallest part of whole-life cost |
| Installation | WRAS plumbing, drainage, three-phase, softener | Skipping it wrecks the machine or fails water-authority checks |
| Running cost | Water, energy, detergent, rinse aid | Repeats every service — often exceeds purchase over 3 years |
| Servicing | Descaling, maintenance, breakdown response | Keeps it running at peak; essential in hard water |
Dishwashers We Stock or Source
Craven Cooling stocks and sources commercial dishwashers, glasswashers, hood-type and pass-through machines to specification. We can size the machine to your covers and throughput, advise on the installation — WRAS plumbing, drainage, three-phase and water softening — and support it with servicing. Tell us your kitchen size, peak covers and water hardness and we will spec the right class. Talk to us via our product range or our servicing team, or call the number below.
In this guide ↓
- Key facts and warewashing reference numbers
- The six decisions that size a dishwasher
- Racks-per-hour sizing maths and the four classes
- The 82°C rinse, water/energy/chemical cost
- Installation — WRAS, drainage, three-phase, softener
- Worked example and buying checklist
- FAQ — eight buyer-objection questions answered
Worked Example: Sizing for a Gastropub
An 80-cover gastropub with a busy Saturday service and a separate bar, sizing its warewashing from scratch. The aim: keep the pass clear through peak and choose an installation that lasts.
For this gastropub, a hood or upper-end undercounter crockery machine rated comfortably above the ~10 racks/hour peak (after derating the rated figure by 30–40%) clears the pass, and a dedicated bar glasswasher keeps glassware gentle and off the crockery machine. If the pub sits in a hard-water area, a softener is non-negotiable; confirm whether the site has three-phase if you step up to a hood machine. Support it with a service contract for descaling and breakdown cover. That is a warewashing set-up that copes with a busy Saturday and survives the hard water.
Dishwasher Buying Checklist
Run through this before you buy. It prevents the three classic failures: a machine that can’t keep up, an install that fails water-authority checks, and limescale that kills the boiler.
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Calculate peak racks per hour Covers × items per cover ÷ items per rack ÷ wash-up hours. Then discount the machine’s rated throughput by 30–40% and make sure it still exceeds your peak.
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Pick the class for your kitchen size Glasswasher for bar/glass, undercounter for café/small gastropub, hood/pass-through for busy restaurant, conveyor for high-volume or institutional.
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Confirm the machine sanitises with a hot rinse A final rinse around the recognised 82°C benchmark is what sanitises and flash-dries. This is the hygiene case for a machine over a hand-wash sink.
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Check the water hardness and plan a softener In hard-water areas fit a softener or regenerate the built-in one with salt. Limescale is the number-one killer of commercial dishwashers.
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Confirm the electrical supply — often three-phase Glasswashers/undercounters run single-phase; hood and conveyor machines often need three-phase. Confirm the site has it before you order.
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Sort WRAS plumbing, backflow and drainage WRAS-approved fittings and the correct backflow device protect the mains; the drain must take the discharge without backing up. Get a competent plumber and keep the paperwork.
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Model the running cost at £0.27/kWh Water per cycle + energy + detergent + rinse aid, times your weekly racks. Over three years running cost can exceed the purchase price.
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Arrange servicing and breakdown cover A dishwasher down at peak stops the pass. A service contract for descaling, maintenance and priority breakdown response keeps it running.
Choose a commercial dishwasher by throughput, then by installation. First, size it: calculate peak racks per hour (covers × items per cover ÷ items per rack ÷ wash-up hours), discount the machine's rated figure by 30–40% for real-service loading, and make sure it still exceeds your peak. Second, pick the class for your kitchen size — a glasswasher for a bar, an undercounter for a café or small gastropub, a hood/pass-through for a busy restaurant, and a conveyor/rack machine for high-volume or institutional kitchens; run a glasswasher alongside a crockery machine wherever there's a busy bar. The commercial cycle is fast and finishes with a hot rinse around the recognised 82°C benchmark that sanitises and flash-dries — the consistency a hand-wash sink cannot match at volume. Model the running cost (water, energy at £0.27/kWh, detergent and rinse aid), which over three years often exceeds the purchase price. Get the installation right: WRAS-approved plumbing with backflow protection, adequate drainage, the correct supply (often three-phase for hood and conveyor machines), and — critically in hard-water areas — a water softener, because limescale is the number-one killer of commercial dishwashers. Add a service contract for descaling and breakdown cover. Craven Cooling stocks and sources commercial dishwashers, glasswashers, hood-type and pass-through machines to specification, and supports them with servicing. Call 01792 732702 or visit the Swansea showroom.
