'I want an instant boiling water tap – will it cost more than using a kettle?'

A Quooker instant boiling water tap
A 'basic' hot tap can cost as much as £850 

My office has a hot tap in its kitchen, and while I think it's great – I'm able to make a cup of tea instantly, rather than waiting for the kettle to boil – I can't help thinking it must use a lot of energy to keep the water at boiling point constantly.

I've looked online and one brand, Quooker, claims it costs just three pence a day to have the boiling water at hand – can this be true? How does that compare with the cost of boiling a kettle? If it's cheaper, or the same, I might get one for my home – though they are fairly pricey.

TP, by email

Like you say, hot taps aren't cheap. Quooker offers two different types of tanks. One, which dispenses only boiling water (100C), can be bought in different sizes, and costs between £850 and £1,120, while the other "combi" tank  which generates both hot (50-60C) and boiling water  is suited to households where the kitchen tap is more than six metres away from where you need to put the new micro-boiler. This costs £1,150.

The heavily insulated tanks, which range from three litres to 11 litres, sit under the kitchen sink and connect to the water supply, while being heated electrically. The water is purified when it passes through the filter, and is dispensed through the Quooker tap.

A rival company Grohe charges £1,407 for a faucet and four litre tank.

Quooker claims that the cost of using its hot tap is one penny per litre delivered, or approximately three pence a day. The cost of boiling a full kettle (which typically holds 1.5 litres) is around 2.5p per boil, according to npower.

This would suggest that a Quooker could save users a significant sum, particularly those who regularly boil their kettle.

But Andy Smale, technical director at Expert Energy, a group of independent energy consultants, calculated that the difference in savings were in fact minimal.

He said that the amount of energy it would take to make six 250ml cups of tea or coffee on six separate occasions with a kettle (typical minimum kettle fill of 500ml) would cost 5.46p per 24 hours, according to these calculations: 3kW x 84 seconds x six = 0.42 kWh. 0.42 kWh x 13p/kWh = 5.46p.

When using the Quooker, the amount of energy it would take to heat 1.5 litres (six 250ml cups) from 15C to 110C would be 4181 x 95 x 1.5 x 2.777778e-7 = 0.1655 kWh. To keep the water hot over 24 hours the amount of energy used would be 0.01kW x 24h = 0.24 kWh. So, the total energy used would be 0.1655 kWh + 0.24 kWh = 0.4055 kWh. This is equal to 5.27p per 24 hours (0.4055 kWh x 13p/kWh).

Although using the Quooker is slightly cheaper, with a basic hot tap costing £850 it would take several years before any savings were actually made.

Stephen Johnson, managing director at Quooker, said that the hot tap would also save home owners a significant amount of water because users only dispense as much water as they need, while many households waste water when using a kettle because they overfill it, reboil it, and because leftover water is often poured down the drain. "A hot tap can save around 100 litres of water a year," he said.

Andy Smale from Expert Energy, said: "Kettles waste energy for a number of reasons – design issues such as over-boiling and heat loss through the body of the kettle can result in over 25pc of the energy used being lost. Even more significant is the typical minimum fill level of 500ml which can mean you end up boiling twice as much water as necessary if you only want to make one 250ml mug of tea or coffee.

"The Quooker is designed with a vacuum-type insulation to minimise heat loss, however if left on standby constantly the amount of heat leaking out is comparable to that which can be wasted using a kettle.

"For example, if you boil water for one 250ml cup six times a day then the savings over using a kettle will only amount to 0.2p per day. If you switch the Quooker off overnight, are a heavy user or are one of the 75pc of people who have a habit of overfilling the kettle then you may save an additional penny a day, however even this will not recoup the Quooker’s purchase and installation costs."

Do you have a question on household bills for our experts? Email us at moneyexpert@telegraph.co.uk or write to Telegraph Money Ask an Expert, 111 Buckingham Palace Road, London, SW1W 0DT.