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Instant boiling hot water taps...transparent costs for the first time

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This article is about the type of instant hot water tap that permanently holds a tank of water close to boiling point to provide instant boiling water in the kitchen.

It does not cover the costs of variations of these products that have other features such as chilling water (which will almost certainly add to costs).

It gives a clear comparison of the annual energy costs of using an instant boiling water tap compared to using a kettle that isn't significantly overfilled.

It is widely thought that instant hot water taps are a cheaper alternative to using an ordinary kettle for boiling water.

The headline results for the most energy efficient instant boiling water tap I have found are:

  • If you drink 20 mugs of tea or coffee a day (around 6.5 litres of boiling water) the annual cost will be SIMILAR to the kettle

  • If you drink LESS than 20 mugs a day, it will cost you MORE

  • If you drink MORE than 20 mugs the instant boiling water tap starts to save you money

For most brands I've looked at you need to drink a LOT more than 20 mugs per day for the instant boiling water tap to be cheaper.

They do of course provide 'instant' boiling water. I can fill and boil my kettle with enough water for two cups of tea in 100 seconds. Not quite as convenient, but a lot cheaper.

I've included a tips sections on both buying and energy saving when boiling water with whichever type of product you use.

The costs below do not take into account the purchase price of instant boiling water taps. These vary greatly and can be many hundreds of pounds.


Cost of energy comparisons

The tables below show the annual running costs for three different situations: homes drinking 10 mugs of hot drinks per day, 20 per day or 30 per day. Of course, water is boiled in homes for other purposes than making hot drinks, and for that reason the total volume of water heated is also given in these comparisons.

The total yearly energy costs are shown in the red boxes.

The comparison is between an ordinary jug kettle and four brands of instant boiling water tap based on technical information the manufacturers have provided me with.

The numbers in each row in the tables below are:

Row A - the cost of the energy used by instant boiling water taps to keep the water hot and "ready" throughout the year. This varies for different manufacturers, and it is known in the industry as the "standing losses".

Row B - the cost of reheating incoming cold water after boiling water has been dispensed.

Row C - the total annual costs (rows A and B added together).

Row D - the average cost per litre of boiling water over a 12 month period.

One assumption in these numbers is that ordinary kettle users overfill their kettles by an average of only 20%. This is quite realistic if you are cost and energy conscious and use the tips below. Over-filling of kettles is something that features increasingly in energy efficiency campaigns.

Other more detailed assumptions are shown at the end of this article.


As you can see in the above case, the kettle costs are cheaper in all cases.


In this example, if you use an average of 20 mugs of tea per day then the costs for the ordinary kettle are very similar to the Quooker but the other brands are still much more costly.


In this case with a higher consumption of 30 mugs of tea a day on average the Quooker becomes slightly cheaper over the year, saving around £16, but the other instant taps are still more costly.

As you saw above the Quooker works out similar to the kettle when you reach 20 mugs of use.

For the other brands to have equivalent costs to a kettle you need to drink the following amounts:

Qettle: 70 mugs/day (22.75 litres)

Fohen: 60 mugs/day (19.5 litres)

Hyco: 35 mugs/day (11.37 litres)

As mentioned earlier the comparisons all assume that if you are a kettle user then you only overfill by 20%. If you typically overfill by 50% then if you drink fewer than 10 mugs a day then a kettle is still cheaper than the Quooker product.


Other intant hot water tap costs and factors to consider

Investment and replacement cost

Given that these products cost several hundred pounds, some over £1000, a unit is a significant investment. Additionally, they will need replacing at some point and so replacement costs need to be considered too. I have not included investment or replacement costs in the above figures. In contrast, kettles are very inexpensive to replace.

Maintenance costs

Some of the manufacturers recommend replacing items such as filters every 6 to 12 months, and these can be costly. This very recent Which article gives a lot of information about this brand by brand.

If you live in hard water areas then descaling of instant boiling water systems needs to be done periodically for some manufacturers, or filters need to be changed. In the case of Quooker for example the kit for doing this is around £50 and my understanding of the cost for a Quooker engineer to do this is around £150.

Descaling a kettle in comparison costs around 60 pence.


One other factor to consider in making a decision for products like this is that although instant boiling water taps do not take up space on kitchen worktops, they do take up space in kitchen base units


Tips on buying instant boiling water taps

Size and effect on cost

Boiling water taps are available with a range of hot water tank volumes. The larger the volume, the more hot water you can dispense before waiting for the unit to warm up again. BUT, the larger tank versions are more costly to run as they lose more heat.

Additional costs of other variations on these taps

Many manufacturers offer products that offer other features such as chilled water, sparkling water and lower temperature instant water for use in sink washing. The standby energy costs of these in kWh will be higher for these more complicated products than for a product that JUST provides boiling water.

Using an instant hot water tap of any sort for sink washing is generally the most expensive way to heat water for a sink. See my other article on sink washing costs for the figures.

Other types of products that call themselves "hot water tap"

Counter top units - these sit on the worktop as freestanding units. Some of these hold a tank of permanently hot water similar to the under-counter products above. I would expect the running costs to be similar to under counter units above.

Cold water tank counter-top units - these units have a tank of water that sits at room temperature, and water is only heated on demand when needed. You can tell which ones these are as the water tank is usually very visible: a simple plastic tank at the back or side of the unit. I would expect the water flow rate on these products to be slow compared to the types discussed in this article, however I would expect the running costs will be very similar to a kettle as they aren't trying to keep a tank of water permanently hot.

Hot water taps for dishwashing - these hot water taps are dedicated to heating and dispensing hot water on demand for use in sink dishwashing, but at a temperature A LOT LOWER than boiling. They do not have standing losses (as far as I am aware). As mentioned above, these are an expensive way to heat water for sink washing.

Getting and calculating the hard £ numbers you need for yourself

In my research I found manufacturers of instant boiling water taps do NOT give enough information publicly to enable you to do the above calculations and comparisons.

From the research and analysis I've done, the information they currently show in their marketing material is consistently and significantly incorrect. These inaccuracies are the subject of a separate blog post on this site.

If you ARE seriously interested in understanding the energy costs of an instant boiling water tap, ask the manufacturer/seller for the "annual standing or standy losses kWh" figure. Accept nothing less. In my communications with them, they initially told me the energy used by the control electronics (a very low figure), and NOT the standing losses figure. An annual standing losses kWh will be at the very MINIMUM 80kWh.

If you multiply the standing losses kWh figure by your tariff you will be able to understand the equivalent figure to row A above in the tables.

So, as an example, if the standing losses kWh figure for a product is 100kWh, if you multiply that by 27p (the current standard electricity tariff) you get £27. This will be the annual cost you are committed to even before you start dispensing water from it.


Tips on how to reduce energy use whichever method you choose

If you are going on holiday turn your instant hot water tap off. There will be an easily accessible switch under the counter next to them. This will be particularly worthwhile for some of the products that are very energy hungry, as from the above tables you can see that the running costs of the manufacturer's products do vary a lot.

Better still, use one of these smart energy monitoring plugs. Then you can turn your system on and off remotely as well at the same time as getting an idea on how much energy it uses on numerous phone apps. These plugs are awesome gadgets; incredibly easy to set up and they use very little energy themselves.

If you use your instant boiling water tap to fill a sink with hot water for washing up it will generally work out around three times more expensive than using your regular hot water if it is heated by gas (and probably more expensive than water heated by oil or propane gas).

When using a kettle, there are two simple methods for avoiding overfilling them.

  • The first is to fill your mugs with tap water and pour the contents into the empty kettle.

  • The second is to mark your kettle like in the picture below to match the mug or cup sizes you use regularly. This is what we do in our house.


The geeky assumptions

  • That kettle users overfill by an average of 20%

  • If you assume that kettles are over-filled by 50% rather than 20% on average, then the Quooker "equivalent cost"/litre point works out at 10 mugs a day not 20

  • Kettle efficiency of 86.7% (as measured on two different kettles with 1 litre of water and a start temperature of 17C)

  • 17C start temperature and 99C boil temperature has been assumed for all calculations on all products above

  • 99% efficiency for all instant hot water taps (assuming 1% of dispensed water is left remaining in the delivery hose to cool)

  • 27p/kWh electricity unit cost

  • Standing losses figures provided to me directly by the respective manufacturers in October 2022

  • Product tank sizes assumed: Quooker 3 litres, Qettle 4 litres, Fohen 2.4 litres, Hyco 3 litres

  • Mug size 325ml


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Mark Thompson

Get Energy Savvy - simple practical home energy efficiency information

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