Hot Water Urn Sizes: 10, 20, 30 or 40 Litres? Cups, Amps and Boil Times Compared

A hot water urn is a large electric water boiler with a tap, used to keep hot water ready for tea, coffee and instant drinks for a group. The common commercial sizes are 10, 20, 30 and 40 litres. As a guide from one maker's figures, a 10 litre urn serves about 50 small cups, a 20 litre urn about 120 and a 30 litre urn about 160. Most urns we sell plug into a standard 10 amp power point, but some faster 20 and 30 litre models need a 15 amp outlet.

This guide compares the hot water urns we sell by litres, cups, power and size, using each maker's own figures.

Hot water urn sizes compared

Size	Model	Cups (maker's figure)	Power	Outlet	Size (mm)
10 litre	Robatherm 10 litre urn	50 cups of 160 ml	2,300 W	10 amp	240 diameter x 480 high
10 litre	Benchstar WB-10	Not stated	2.0 kW	10 amp	210 x 280 x 450
20 litre	Robatherm 20 litre urn	120 cups of 160 ml	2,300 W	10 amp	330 diameter x 550 high
20 litre	Benchstar WB-20/10	Not stated	2.3 kW	10 amp	265 x 320 x 510
20 litre	Benchstar WB-20	Not stated	2.5 kW	15 amp	265 x 320 x 510
20 litre	Apuro HF151-A hands free	Not stated	See listing	10 amp	375 x 319 x 590
30 litre	Robatherm 30 litre urn	160 cups of 160 ml	2,300 W	10 amp	330 diameter x 645 high
30 litre	Benchstar WB-30/10	Not stated	2.3 kW	10 amp	350 x 420 x 550
30 litre	Benchstar WB-30	Not stated	3.0 kW	15 amp	350 x 420 x 550
40 litre	Apuro HF153-A hands free	Not stated	See listing	10 amp	440 x 383 x 640

What size hot water urn do I need?

Count the cups you pour in your busiest break, then allow a margin so the urn is never run low. Robatherm rates its urns in 160 ml cups: 50 from 10 litres, 120 from 20 litres and 160 from 30 litres. A mug is bigger. At 250 ml a mug, simple division gives 40 mugs from 10 litres, 80 from 20, 120 from 30 and 160 from 40, if you drained the urn completely, which you should not.

• 10 litres: a staff room, a small meeting, a market stall.
• 20 litres: a function room, a church hall morning tea, a canteen.
• 30 to 40 litres: conferences, sports clubs, school events and catering.

Bigger is not always better. A large urn takes longer to boil and holds more water hot all day. Two smaller urns can be easier: one on, one ready to swap.

How long does an urn take to boil?

It depends on the litres and the element. Apuro lists the boil time for its hands free urns: 50 minutes for 20 litres and 99 minutes for 40 litres, on a 10 amp plug. So fill and switch on well before people arrive, and top up in small amounts so the urn recovers quickly.

10 amp or 15 amp?

A standard Australian power point is 10 amp. A 15 amp plug has a larger earth pin and will not fit it. This matters for halls, clubs and hired venues, where you rarely know what outlets you will find.

Benchstar sells its 20 and 30 litre urns both ways. The WB-20 is 2.5 kW on a 15 amp outlet and the WB-30 is 3.0 kW on a 15 amp outlet, for faster heating. The WB-20/10 and WB-30/10 are 2.3 kW versions for a normal 10 amp power point. Robatherm lists its 10, 20 and 30 litre urns at 2,300 W on 10 amp. If the urn travels, buy 10 amp.

Features worth having

• Temperature control. Robatherm urns have a mode selector for variable control or a pre-set 95 degrees. Benchstar urns have a dial with a working range of 30 to 100°C. Apuro hands free urns adjust from 30°C to 98°C.
• Boil dry protection. An urn left on empty will damage its element. Robatherm lists boil dry protection, and Apuro lists a thermal safety reset button on its energy saving urns.
• A water level gauge. Robatherm lists a sight glass and Benchstar a tap with a water level indicator, so staff can see when to top up.
• Double wall insulation. The Apuro energy saving urns (10 to 40 litres) have a double-walled, insulated body; Apuro states this reduces energy use by up to 60% compared with single-skinned urns. Robatherm lists a double skinned tank.
• Hands free tap. The Apuro HF151-A and HF153-A dispense without touching the urn, for self-service areas.
• A non-drip tap. Listed on both Robatherm and Benchstar urns.

Urn, percolator or water boiler?

• Hot water urn: manual fill, portable, heats a tank of water and holds it. No plumbing.
• Coffee percolator: looks like an urn but brews coffee in the tank. The Apuro CN295-A percolator holds 15 litres, listed as 100 cups, at 1.5 kW. See kettles and percolators.
• Coffee machine: if you sell coffee rather than offer it, see commercial coffee machines.

Setting up a whole tea and coffee station? Browse our cafe equipment.

Using an urn safely

• Put it on a stable bench away from the edge, with the cord out of reach.
• Never fill past the maximum mark or switch on below the minimum.
• Let it cool before moving it. A full 30 litre urn holds 30 kg of near-boiling water.
• Descale regularly in hard water areas so the element lasts.

Frequently asked questions

What is a hot water urn? A large electric water boiler with a tap at the front. It heats a tank of water and keeps it hot so people can make tea, coffee and instant drinks without waiting for a kettle.

How many cups does a 10 litre hot water urn make? Robatherm lists 50 cups of 160 ml from its 10 litre urn. In 250 ml mugs, 10 litres divides into 40.

How many cups does a 20 litre urn make? Robatherm lists 120 cups of 160 ml from its 20 litre urn. In 250 ml mugs, 20 litres divides into 80.

Will a 30 litre urn run on a normal power point? Some will. The Robatherm 30 litre urn and the Benchstar WB-30/10 are 10 amp. The Benchstar WB-30 is 3.0 kW and needs a 15 amp outlet.

How long does a 20 litre urn take to boil? Apuro lists 50 minutes for its 20 litre hands free urn on a 10 amp plug. A higher wattage 15 amp urn heats faster.

Sources: each model's capacity, cups, power, outlet and size as listed by its maker on our product pages.