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

The key information in this article contributed to the BBC Radio 4 Sliced Bread show streamable here.

To see lots of other Savvy Stuff Blog articles click here

Headlines

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 as an alternative to a kettle.

It does not cover the more complicated variants of these products that have other features such as chilling water.

It gives a clear comparison of the annual energy costs of using these instant hot water taps compared to using an ordinary kettle.

It is a common perception that instant hot water taps are a cheaper to run than a regular kettle for boiling water and that they save you both energy and money.

My analysis suggests that compared to the most efficient instant tap I assessed (the Quooker), a household drinking around 10 mugs of tea or coffee a day:

• Will have energy costs around £10 lower using a kettle than the Quooker. This assumes some care when filling the kettle to reduce overfilling.

• Only by drinking more than 23 mugs of tea a day would the Quooker result in lower energy costs. This equates to consuming 7.5 litres a day of boiling water. This "break even" figure is higher for the other brands of tap I evaluated. Some were much higher.

• If a household chooses to continue overfilling their kettle as they do today (typically 50% overfill) then the annual energy costs of a kettle will be virtually the same as a Quooker.

  
  

An instant boiling tap only saves significant energy overall if you use a LOT of boiling water such as in a commercial office situation.

Instant boiling water taps do of course provide 'instant' boiling water.

Boiling enough water for two mugs of tea in my own kettle takes 90 seconds.

The kettle isn't as convenient, but in my view based on my analysis, they are a lot cheaper overall in most normal household situations.

This article includes a practical tips sections on buying instant hot water taps.

The costs below do not take into account the purchase price of instant boiling water taps. These vary greatly, from several hundred pounds to over a thousand pounds plus installation.

---

How instant boiling water taps use energy

There may be misunderstandings about how much energy instant boiling taps use.

They use energy is used in three ways

1. Energy to keep the water hot and ready for you to use. This is because although the storage tank under the sink is well insulated, it still loses heat. This needs to be periodically re-heated throughout the day to keep the water at the desired temperature.

2. Energy to heat up NEW (cold) water that goes into the storage tank to replace hot water that you have actually used.

3. They lose or waste some energy when the hot water is dispensed. Some (including Quooker) waste as much as 9% of the heat energy during dispensing.

---

Kettles energy use and kettle efficiency

For kettles, the only energy used is boiling cold water each time you use it.

Kettles are actually pretty efficient things, between 85 and 90% efficient according to a number of academic studies. I've measured several kettles myself and found their efficiency is very consistent in the 86-87% range.

When boiling a kettle, the main ways energy is wasted are

• Steam escaping into the room through the spout when heating up (most of which is in the final stage of boiling)

• Heat escaping through the side walls to the room as it is heating up

• Heating the body of the kettle

The biggest "inefficiency" factor contributing to the running costs of a kettle is overfilling it and boiling some water unnecessarily. It is widely accepted by experts that kettles are typically overfilled by 50% in households.

This wastage adds up in the long term and understandably features from time to time in energy efficiency campaigns. The Energy Savings Trust suggests that reducing overfilling of a kettle will save the typical household around £10 a year.

With a little care when filling a kettle it is quite easy to reduce overfilling a kettle. Reducing overfilling to 20% is pretty easy to achieve in my opinion, although some kettle designs make this harder for householders to do. Tips later on how to easily reduce overfilling.

---

Energy cost comparisons - kettles vs instant taps

The tables below show running cost comparisons between an ordinary jug kettle and four brands of instant boiling water tap based on the manufacturers own technical information.

The tables below show the annual running costs for three different quantities of mugs of tea or coffee drunk each day :

• 10 mugs of hot drinks per day (this is slightly more than the national average)

• 20 mugs per day

• 30 mugs per day

Of course, water is boiled in homes for other purposes than making hot drinks, such as for cooking. For that reason the total volume of water heated is also given in the comparisons below.

I am assuming a 20% overfill of the kettle in these initial tables. Other scenarios are shown later. Other more detailed assumptions are shown at the end of this article.

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 and available" 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 fresh cold water to replace the boiling water that has been dispensed by the instant hot water tap.

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

Row D - the average cost per litre of boiling water for each type of product.

The total yearly energy costs are shown in the red boxes. This is JUST the energy costs. Costs of purchase or maintenance of instant taps are covered later in the article.

---

As you can see in the this 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 still slightly cheaper than Quooker. 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 £6 a year. But 30 mugs of tea is around 2 gallons of boiling water per day, a bucket full of boiling water...every day!

Even when boiling this much water, the other instant tap brands are still more costly to run than a kettle.

---

Conclusions...so far

As you saw above the Quooker works out similar to the kettle when you reach 23 mugs of use.

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

Qettle: 65 mugs/day (21 litres/day)

Fohen: 53 mugs/day (20 litres/day)

Hyco: 32 mugs/day (12 litres/day)

As I said before, this assumes a little care is exercised when filling kettles, reducing overfilling from 50% to 20%.

How costs work out if you want to carry on overfilling your kettle?

The table below shows the comparative costs if you carry on being the typical household overfilling your kettle by 50%.

As you can see, whether you use a kettle or a Quooker annual energy costs work out virtually the same.

The kettle is still cheaper than using the other instant tap products.

And, finally, these are how the numbers work out if you habitually overfill by double every time you use the kettle, so you always boil twice the amount you need.

Some of the instant taps finally win out....though purchase and maintenance still isn't taken into account.

---

Other instant hot water tap costs and factors to consider

Investment and replacement costs

Given that these products cost several hundred pounds, some over £1000, these products are 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 and will last 4-5 years or potentially much longer. The established players design goal is 7 year lifetime.

Sustainability kettles vs instant taps

But what about the carbon footprint or sustainability of manufacturing of these products? An instant hot water tap might last 20 years. Kettles rarely last that long.

There are studies that calculate the carbon footprint of kettle manufacture but I can find nothing that allows a comparison with the carbon footprint of manufacturing instant hot water taps.

One simple way to answer this is to look at the material weight of each type of product.

• An empty kettle weighs a little over a kg.

• Instant tap units weigh many times that figure, usually in the 8-10kg range, some more.

A simple conclusion is that, based on the materials content used, the carbon footprint of the instant tap might be 7-8 times that of a kettle.

Maintenance costs

While I’d expect reliability of these products to be pretty good they do have maintenance needs that are important to give them a good lifespan. Some of the manufacturers of instant hot water taps recommend replacing items such as filters every 6 to 12 months, and these can be costly. This 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.

Space

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 typically more costly to run as they lose more heat sitting there permanently hot in your cupboard.

Additional costs of other variations on these taps

Many manufacturers offer products that offer other features such as chilled water, sparkling water, water filtration and lower temperature instant water for use in sink washing. In my opinion, the standby energy costs of these in kWh are likely to be higher for these more complex 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 in the cost comparison tables above.

Cold water tank counter-top units - these units have a tank of water that sits at room temperature. Water is only heated on demand. You can tell which ones these are as the water tank is usually very visible. This is usually a simple clear sided 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. I would though expect the running costs of this type of hot water will be broadly similar to a kettle.

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, direct use of electricity to heat water is usually the most 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.

This was the reason I researched and wrote this article. The facts on this for the first time.

From the research and analysis I undertook for this article (Autumn 2022), the information the manufacturers showed in their marketing material was consistently and significantly incorrect or misleading in my opinion. These inaccuracies are the subject of a separate blog post on this site and a complaint to the Advertising Standards Agency that was upheld.

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 standby losses kWh" figure. Accept nothing less.

In my communications with manufacturers, some 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 figure 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 24.5p (the standard variable energy rate from October 2024) you get £24.50. This will be the annual cost you are committed to even before you start dispensing water from it.

---

Tips on how to reduce energy using an instant hot water tap

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.

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 approaching three times more expensive than the more traditional arrangement of water from the tap heated by gas (and very likely more expensive than water heated by oil or propane). See my other article on this.

How to easily avoid overfilling a kettle

Three straight forward ways:

1) Make sure you have a kettle that allows you to boil as little as 0.25 or 0.3 litres. Many Bosch, Tefal and Philips models allow this, but some others may too.

2) If you have a kettle without a visible level indicator on the side, I suggest you junk it and get one that has. It will pay for itself in the long run.

3) Most importantly, ignore the markings on the fill window. Make your own. Find the largest mug (s) you use regularly and use them to fill your kettle mug by mug. Mark up the kettle with a Sharpie pen as I've done here with ours. It makes it super easy to fill really precisely.

Simples! :-)

---

The geeky assumptions and facts

• Kettle efficiency used in calculations was 86%. This was based on

  • Academic studies citing kettle efficiency at between 85 and 90%.

  • Measurements on two different kettles with 1 litre of water and a start temperature of 17C. The average figure was actually 86.6%). I know of other people who have measured this on their own kettles with near identical figures.

• A long term study of 250 UK homes measured the actual energy use of kettles over an extended period. The study found average use of 167kWh across the households observed, (which were all owner occupier homes with diverse occupancy). Assuming the kettles were all around 86% efficient, and that overfilling was 50%, this implies a daily net boiled volume of around 2.6 litres, around 8 mugs.

• 17C start temperature and 100C boil temperature has been assumed for all calculations on instant hot water tap products above with the exception of the Quooker at 108C

• A 17C start temperature is felt to be a perfectly reasonable figure given there are usually several metres of cold feed pipe between a tap and the incoming ground mains. Topping a kettle up will always start with a volume of water from the local pipework at room temperature (140ml per m of 15mm copper pipe) followed sometimes by colder water from the mains riser.

• 0.0966kWh thermal energy required to raise the temperature of 1 litre of water from 17C to 100C

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

• Quookers and some other brands heat the water above 100C under pressure to 108C, effectively superheating it. They do this to guarantee that the dispensed water is no lower than 100C. They actually do this by cooling this "superheated" water by aerating it as hot water is dispensed. This process creates steam during dispensing, which is effectively wasting heat energy into the air around the tap. This is why Quookers can be quite energetic and steamy when used.

• 98% efficiency is assumed for the brands of instant hot water taps that do not heat above 100C. This is just a working assumption in the absence of actual data, assuming there will be losses such as hot water left in the delivery pipework that simply cools.

• I have assumed that during 6 months of the year, the heat loss from the instant hot water tap results in a small reduction in the heating costs of the home. I've assumed a gas boiler, efficiency of 88% and with a ratio of electricity/gas unit cost ratio of 3.92 (representative as of Nov 2024)

• 24.5p/kWh electricity unit cost. This is the typical Ofgem energy cost price cap from October 1st 2024.

• 2022. As of October 2024 the best of the products, the Quooker is unchanged. It is unknown if the others have changed.

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

• Mug size assumed is 325ml

This article was originally published on Oct 24 2022.

---

Do subscribe for updates if you like what you've read here.

I run this website as a hobby, because I care about this stuff, and do it for no commercial purpose. If you have valued what you've seen, please tell other people about it.

If you have any other suggestions for additions or changes to site content do please let me know. While I have made every effort to ensure that the information contained on this website is correct, I cannot take responsibility for errors or omissions.

All content on the site should be treated as information and not advice. You should take professional advice where appropriate to different site articles.

Thanks.

Mark Thompson

Get Energy Savvy - simple practical home energy efficiency information