Sliced Bread's overall conclusion of boiling water taps (and the Quooker in particular) was that they were more BS than SB. However, I do have a few gripes about their analysis.
The Quooker is the most efficient boiling water tap largely down to the excellent insulation of its hot water tank. The energy expert used by Sliced Bread, to calculate the relative costs of a boiling water tap versus a modern electric kettle, made a number of assumptions:
- 10 mugs (300 ml/mug) of tea or coffee per day
- Electric kettles are 85-90% efficient (the Quooker is about 91%) so 87.5% used in calculations
- Kettles are 'overfilled' by 20%
- Standing losses (i.e. the amount of energy used to maintain the boiled water in the tank at boiling point) for the Quooker were £19/year. By definition, the standing losses for a kettle are zero
Based on these assumptions, the annual running cost for the kettle was £38 compared to £49 (including the £19 standing losses) for the Quooker. These cost figures are for the UK and their absolute magnitude will depend on where you live. [note: the actual costs/energy for raising the water temperature from ambient to boiling point are lower - £30 compared to £38 per annum - for the Quooker due to its greater efficiency and 0% overfill). SB's energy expert calculated that the Quooker boiling tap and an electric kettle have identical running costs when the daily usage reaches 23 cups (7 litres) per day. Which is a lot of cups of tea/coffee, but more on this later.
Quooker's own calculations assume a 50% overfill and a kettle efficiency of 72%; in which case the break even point for the two appliances is only 7 cups of tea/coffee. Quite a difference!
This led to an interesting discussion with the SB's energy expert. Apparently, the standard 'overfill' value, based on most studies, is 50% and not the 20% assumed for his own calculations. Note that the running cost of an electric kettle would increase from £38/year to £47.50/year assuming a 50% overfill. His argument for the lower figure was personal choice. I'm sorry but personal opinion is irrelevant and he should have used the industry standard of 50% in his calculations; he can argue the benefits of reduced overfilling after presenting the standard data. In my experience most people overfill nearer the 50% mark for a number of reasons:
- boiling water for cups of tea is not considered a major energy use/cost
- kettles have a minimum volume (e.g. 500 ml) which represents a 60% overfill for a single cup
- you might be considering having a second cup, so you put in extra just in case
- the kettle is some distance from the tap, so why not fill it up to save time later
- I'll put extra in the kettle in case someone else wants a drink
- Not strictly overfill but I estimate about 1-in-4 kettle boils produces no end-product due to forgetfulness, a phone call/visitor, distraction, etc
Then the expert, after using a non-standard overfill value for his own calculations, has the nerve to question Quooker's kettle efficiency figure (72%) by stating he has no idea where they got that value. Well, I found
this resource very easily which puts the efficiency of electric kettles at 80% and electric stove top kettles at 70%. Consider also that people use kettles on gas stoves which are about 50% efficient. Remember that Quooker is an Australian product where the cheapest way to heat water is gas. If modern electric kettles are indeed 85-90% efficient (and I've no reason to doubt that), older kettles that have furred up with scale could well be only 80% efficient or less. So, using fairly standard assumptions of 50% overfill and a kettle efficiency of around 80% (includes old & new plug-in electric, stove top gas and electric), the Quooker's running costs will be lower than a modern electric kettle.
The energy expert on SB made the mistake of comparing a new high efficiency electric kettle with the Quooker boiling tap. I'm not sure consumers buy the latest highly efficiency kettle and then suddenly think: I wonder if a boiling tap would be better? More likely, the old kettle has given up the ghost and the choice is between a new kettle or a boiling water tap. Both, clearly, will be more efficient than the old kettle and a new kettle will be the cheaper option (perhaps vastly cheaper option). People are more likely to go for a boiling water tap if they are having a new kitchen installed and want the convenience, extra facilities (e.g. chilled and sparkling water), and reduced clutter that the boiling tap offers.
Earlier in the blog, I talked about the break even point in running costs between an electric kettle and the Quooker boiling water tap. The SB expert suggested this was 23 cups of tea/coffee whereas Quooker put the figure at 7 cups. I have made an argument for the 'true' value to be nearer that suggested by Quooker if we use the normally accepted assumptions. Let's say the break even is around 10-12 cups of tea/coffee (3 to 3½ litres) per day. Our two-person household easily meets this requirement just in tea and coffee alone. Add in using boiling water for making porridge, soup, cooking vegetables, rice & pasta, sanitizing chopping boards, re-hydrating pulses, bread making, pre-warming teapot, crockery, etc etc then we are comfortably using about 6 litres per day. I estimate our boiling water tap saves between £25-50 per year in running costs which means it would take about 20 years to recover the initial investment. I think both SB and I are in agreement about this figure.
In conclusion, the Quooker boiling water tap is well engineered albeit on the expensive side. Cheaper options (about 75% cheaper) are available. You are unlikely to get your investment back as Quooker's predicted lifetime is only 13 years. Our tap is 10 years old. The more it is used the better the value which explains its use in office/industrial situations where a boiling water tap may increase productivity.
We enjoy the convenience and time-saving as much as anything else. And time is money. With the Quooker, the hot water exits the tap at about 102 ℃. I have accidentally put my hand under the tap and not suffered burns (I obviously removed my hand asap) due to the in-built safety features.
Black tea requires a temperature of around 90-98 ℃ whereas green & herbal teas prefer 80 ℃. Coffee brewing requires a temperature of around 94 ℃. If you are brewing your tea in a mug, pour the boiling water directly onto black tea (do not pre-warm the mug) but for green tea fill the mug with boiling water, wait one minute, and then add tea. If you are preparing a cafetiere of coffee, pre-warm with boiling water, add coffee grounds and fill with boiling water. The best tea is made with freshly boiled water containing lots of dissolved oxygen - this is what you get with a boiling water tap. Never reboil water in a kettle if you want a decent cup of tea!
We live in a moderately soft water area so there is no great need to descale water heaters. For hard water areas you should consider adding some form of scale removal/water softening at extra cost.
Boiling water taps have a lower carbon footprint (about 50% lower) than electric kettles because they only boil the amount of water you need and are more efficient heaters.
Posts
