## Do you fill your kettle?

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I seem to remember from school science lessons that water needs a lot of heat to raise its temperature per degree. I suppose this is why a lot of kettles are rated at 3kw to make the boiling process tolerably quick. It surprises me how many people double (or more) this time by putting a lot of water in their kettle, even filling it as a matter of course, when only a very limited amount is needed. The remaining water is then left to gently return to room temperature. This seems to me a great waste of energy which is being carried out by millions of us several times a day. I suppose if you are heating your kitchen and have your thermostat there the warm water left to cool will heat your room, and turn your heating off slightly earlier but in summer this is a total waste, and electric space heating is generally not economic.

For a number of years, here at Wilko Towers, we have kept a measuring jug with the two mug level marked and use this most of the time to “fill” the kettle. The indicator on the kettle itself isn’t accurate and is hard to see and the jug system is very little trouble when it becomes a habit. Assuming we have say 5 hot drinks each per day, how much energy are we saving over a year and how many power stations could we dispense with if this were everyone’s practice? I know lots of people on here like to spend time working out such things, but it’s not my thing. I’d just like to know the answer.

> I’d just like to know the answer.

42.

It's either that, a benign dictatorship or a Skoda Octavia.

T.

But, assuming an excess of one litre of 15C water, raised to boiling, that's

1000 * 4.2 * 85 = 357000J

Check sanity by looking at the time for a 3kW kettle:

357000/3000 = 119s

So, energy used to boil excess water

357000 * 5 * 365 = 650 MJ

Looking at it another way, consider the average excess power (energy per day/seconds per day)

357000 * 5 / (24*60*60) = 20.6W

If you're not using your central heating, it's wasted energy. If your central heating is on, the excess energy will, as you suggest, warm your house a little. Electrical heating is 100% efficient at point of use (theres a lot of loss in conventional generation and distribution).

> 42.

Not far off - specific heat capacity of water is 4200 joules/kg

I tend to get around this by not really drinking hot drinks.

On the occasions I do make a cuppa, I try and only fill the kettle as much as is needed at the time.

My wife is paranoid about only boiling enough water to meet requirements, and not at all keen on re-boiling water that has stood for a couple of minutes. I would rather over-fill slightly (to dissipate the excess heat in the element quickly, after pouring) and I anticipate the point of boiling getting close and switch off without waiting for significant steam to be raised, using the residual excess heat in the element to just finish the boil. Generating steam uses about 7 times more energy than heating water, if I remember right.

Neither of us thinks very much of the other's preferences...

I recently bought a new kettle. The old one, same 1.7L capacity and very similar in design as the new one, needed to be filled to a minimum level each time (approximately 3 mugs "to protect the element" according to the destructions) but not so the new one apparently, which has "1 cup" and "2 cup" level indicators on a pole inside.

Alien stealth elements, that's the future.

On a practical level, I sometimes measure water into the kettle by filling my chosen mug with cold water then pouring the mug into the kettle. Perfect amount of water will be boiled!

I usually wait a couple of seconds for the bubbling to die down after it switches off so hopefully the element won't overheat. My kettle is several years old and no sign of failure.

To take captain paranoia's calculations further, if the average waste power per kettle is 20.6W then we can work out the UK total assuming every household has one kettle:

20.6W * 27.8 million households = 573 MW

In practice I think this is probably a massive overestimate as I suspect most households don't fill kettles up with 1 litre of wasted water 5 times a day, but still taking this forward it is approximately:

one AGR nuclear reactor (so half an AGR nuclear power plant);

or one seventh of Drax at its historical peak;

or a small/medium sized gas fired power plant;

or a medium sized offshore wind farm (eg Race Bank, 75 Square km, 91 turbines) at full capacity in ideal conditions;

or one and a quarter of the UK's largest wind farm (Hornsea One, 407 Square km, 174 turbines, each 190m tall) running at average capacity.

Bit of a kettle tangent, but my niece went for a girls’ weekend at Pontins a month or so ago. Her friends said bring everything, sheets, towels, kettle etc as it’s bit skanky. Why bring a kettle she asks? Well, last time we were here someone had shat in the kettle in the room.

Boil that one up 😃

What about efficiency difference of filling from the hot tap rather than cold? Is it more efficient to have had those first few degrees come from the boiler?

I always take it from the hot tap but my husband always looks at me like I have 2 heads for doing that!

Depends on your water heater, but loft mounted water tanks in old buildings we're notorious for collecting dead pigeons etc.

Still lingers in the back of my mind somewhere, even though we have a sealed system, I prefer cold from the tap.

> What about efficiency difference of filling from the hot tap rather than cold? Is it more efficient to have had those first few degrees come from the boiler?

> I always take it from the hot tap but my husband always looks at me like I have 2 heads for doing that!

We had a very similar discussion a few years ago and I did the experiment.  It's easy enough to get a good estimate of the energy going into the water by multiplying the power rating of the kettle by time.

https://www.ukclimbing.com/forums/off_belay/boiling_a_kettle-526272?v=1#x7085944

Spoiler alert - it takes less than double the time when you put twice as much water in the kettle.

I try to add just enough water. The kettle tends to over-boil a bit before it clicks off so, if I'm anywhere near the kettle, I manually flick it off.

I can't understand why anyone would boil more than they need but there is a guy at work who insists on boling about three mugs worth because he 'doesn't like the idea' of pouring the bottom bit of water out of the kettle.

What he says.

Surely the frugal should be taking a flask to work and coming home with a litre of hot water every day? That's real money saving.

I recall a bizarre incident ar work (years ago). There was a full kettle of hot water, recently boiled when a guy pours all that water, about a litre, down the drain and proceeds to fill the kettle just for one cup. When I commented he said he thought he’d prefer his tea made with freshly boiled water.

I too only put the required amount of water in the kettle. I also refill after boiling to extract residual heat from the element. This warm water either radiates heat away or is used for cooking (rice perhaps) or into the washing bowl. Another economy I use is cooking rice/pasta. After getting it to the boil, I switch off the power and cover it with a towel. They always turns out fine.

Not necessarily cost efficient vs a kettle, but most instant boiling water taps (e.g. Quooker) offer a better energy efficiency, along with a few other conveniences (can give better tasting water, no wait time, etc). Be careful in selection however as some are not as energy efficient vs kettle as others.

You might be better having a 2 minute timer in your shower.  Saves far more energy.

I do this as well.

Always have done. Lids are a remarkable energy saver

At home I would reuse water if there happened to be some freshly heated in the kettle.  In other situations I've come across loads of people who fill kettles from hot taps and I have a deeply seated dislike of that so I do tend to refill unless the previous user is around to ask.

Having grewn up in earlier times I don't think I'll ever reconcile myself to drinking stuff from the hot tap if it can be avoided

I try to use only as much water as needed when filling.

Post edited at 09:28

Ours is a combi boiler, so totally safe.

His logic is like yours, that it just doesn't sit right with him, even though he knows it's perfectly fine

> What about efficiency difference of filling from the hot tap rather than cold? Is it more efficient to have had those first few degrees come from the boiler?

> I always take it from the hot tap but my husband always looks at me like I have 2 heads for doing that!

The first problem is this is wasteful of water (assuming you run the water through the tap until it gets hot). Next, you fill the kettle with hot water (or do you only put a cup full or two in?) leaving a volume of water as great or greater than that in the kettle, to go cold in the pipes, thus wasting much more than you save.

The only way this works is if you have an 'instant water heater' at the sink (but if that uis electric it's no different to the kettle) or if you were running water for washing up anyway and you piggy back your kettle fill while doing that.

I fill the kettle to the volume I require, or the minimum volume to cover the element - whichever is less. I will re-boil the kettle if it isn't empty.

I can't bring myself to fill the kettle from the hot tap though. Although my current house has a combi boiler and would be perfectly fine, I grew up in houses with loft-mounted tanks and it was drilled into me not to drink from the hot tap!

Same here, but I've got to filling it from the hot tap while feeling funny about it, sometimes I do, and sometimes I don't.

Those TV adverts that tell consumers if everyone only boiled the water they needed for a cup of tea, we could "save enough energy to blah blah blah" really get on my nerves. Where are the adverts telling millionaires not to use so many private jet journeys where a flight on BA would suffice?

Having worked in the private jet industry and managed thousands of flights, I promise you some people's weekly carbon foot print is bigger than my lifetime carbon footprint, so feel free to put as much water in your kettle as you like 🖕🏻

The problem for me is that having worked for a while in a representative organisation providing services (including advisory stuff) for HVAC I remember loads of maintenance schedules being updated to include Legionella precautions that no one foresaw.  For that reason I would never like to take water from anything but the cold system as anything with heating involved could imho allow damp warm places for legionella and other stuff to colonise.  I'm simply not prepared to say I know enough about it to know it may be allright and even so people have failed to perceive fatal hazards arising from this stuff in the past - so I'll just stick to ingrained habits thank you and use the pipes and kettles designed to hold water for human consumption.

Post edited at 12:49

> Those TV adverts that tell consumers if everyone only boiled the water they needed for a cup of tea, we could "save enough energy to blah blah blah" really get on my nerves.

The idea that "every little helps" irritates me too.

The average home burns 12000kWh of gas a year for heating. Boiling an extra litre of water, 5 times a day, would consume about 7.5kWh per year. That's about 0.06% of the heating.

Better stick the kettle on, make an extra cuppa and write to MP's about building standards and upgrading our housing stock.

Post edited at 13:13

I'm 53 and I thought putting just enough water in for how many brews you need had been around forever??

E

> I recall a bizarre incident ar work (years ago). There was a full kettle of hot water, recently boiled when a guy pours all that water, about a litre, down the drain and proceeds to fill the kettle just for one cup. When I commented he said he thought he’d prefer his tea made with freshly boiled water.

I used to work with a woman who kept pouring water away that had been brought into the office from the tap in the canteen in a topped-up gallon container and refilled it every time she made a drink.

Stated reason:- she wanted fresh water, not stale !

A key book to read if you want to think about these things is Sustainable Energy – without the hot air by David McKay.

In this book he has a really strong statement.

"If everyone does a little, we’ll achieve only a little."

Anyone wishing to take their kettle miserliness to the next level should invest in a kettle that heats to different temperatures depending on the drink. Ours does water for coffee to 95 degrees, water for tea to 85 degrees. Allegedly this makes the drink taste better (for tea I think they're quite right), but I did work out that you'd probably save the additional spend on the kettle over its lifetime.

Plus you can smugly tell whoever's in the seat next to you about your environmental credentials when you're on the plane to your New York city break.

That sounds like a sensible approach.

Post edited at 14:24

According to captain paranoia's post further up the thread, boiling 5L of water every day for a year requires 650MJ, which is about 180kWh. It's still only 1.5% of your "average home" gas usage, but it's not completely negligeable. Although admittedly boiling 5 litres of extra water a day is quite unlikely (I hope!)

As an aside I fill my kettle in the morning (for our two cuppas) and use the residual hot water to wash up the few items generally left from the night before. It basically saves me running the tap for ages to get hot water off the boiler

But surely if you have a mixer tap (which most of us do, don't we?) then anything untoward in the pipes ends up in your cold water anyway?

> But surely if you have a mixer tap (which most of us do, don't we?) then anything untoward in the pipes ends up in your cold water anyway?

No, there are two separate routes for the water right up tothe spout.

> Ours does water for coffee to 95 degrees, water for tea to 85 degrees

That's the wrong way round, surely? You want just under boiling for tea, cooler still for coffee.

> The idea that "every little helps" irritates me too. >

I don’t understand this. It’s a form of that awful whataboutery which ends so many arguments. We can always rationalise by finding some other person or thing and use that to justify our inaction. I would never suggest that just using as much kettle power as you need obviates the need to do or stop doing loads of other things. I’m sure there are many other little changes we could make which you could also scoff at, but these things don’t do any harm and do some, if very small, good. I’m going to suggest we don’t leave the fridge door open while we fill a milk jug or butter a slice of toast. As the Scots say, many a mickle…..

180kWh is the correct figure (for 5L every day, which seems high but not inconceivable - you could imagine someone leaving an excess of 500ml every time and boiling the kettle ten times a day).

Or £25pa, if you prefer it in those terms.  Or a total of 61 hours wasted, staring at the kettle (assuming 3kW)...

On the other hand where does the waste heat go? in warm times it is surely waste but during cold times it heats your house and less heat input is required elsewhere.  If you have a well designed kettle* and heat electric it's very little waste when it is cold.

* This means something that keeps the steam in. A big open pan cools by evaporation - the heat ends up in your room (once the water has condensed) but makes things damp which you don't want.

True enough, if you have electric heating and an electric kettle (or indeed if you have gas heating and a kettle you heat on the gas hob).  For the months when you're space heating anyway, it's a moot point.

But if you have gas heating and an electric kettle then it's approx five times the price per kWh. It's also much more efficient in terms of CO2/kWh to burn the gas directly in your house, than to burn it in a power station, generate electricity, transmit that electricity and then heat the kettle.

Also, if you pour the hot water down the drain then you're losing all that heat energy.

That's not always the case. Most European mixers (including ones bought in this country) mix internally and only have a single pipe to the spout.

> On the other hand where does the waste heat go? in warm times it is surely waste but during cold times it heats your house and less heat input is required elsewhere.

See the OP

Apparently stove top kettles are most efficient, which doesn't directly answer your question, but might help more generally. I don't have the patience to overfill my stove top kettle, seem to have found the knack for filling it just enough for my morning couple of cups of tea and coffee before it needs refilling.

Post edited at 18:13

I had a colleague who did that.  He’d also volunteer for half day Saturday overtime checking the labs so he could get his flask filled before going into town to do his shop, and charge mileage to the company for the commute so he was only paying for himself to drive the final 3 miles into town and back.

Where as my first mentor never went to the loo in the morning at home.  One year he worked his socks off and didn’t get a pay rise. He retreated to the loos to calm down, and while sitting on the throne worked out how much the company were paying him to have a shit.  From that day on he waited till work, and always had a smile on his face after visiting the facilities!

> He retreated to the loos to calm down, and while sitting on the throne worked out how much the company were paying him to have a shit.  From that day on he waited till work, and always had a smile on his face after visiting the facilities!

Saving the paper and the water if on a meter at home, smart. Tips you just don't get off Martin Lewis.

> I had a colleague who did that.  He’d also volunteer for half day Saturday overtime checking the labs so he could get his flask filled before going into town to do his shop, and charge mileage to the company for the commute so he was only paying for himself to drive the final 3 miles into town and back.

I hate to ask and seem like I'm judging him, but did he manage to have fun in life as well?

I can't help wondering, hopefully he did...

Post edited at 19:44

> Saving the paper and the water if on a meter at home, smart. Tips you just don't get off Martin Lewis.

One office I worked in had a toilet just inside the front door which couldn’t be seen unless someone was going in/out of building as the reception was further along the hall around a corner. One year for many months toilet rolls were disappearing every week and staff came under suspicion. However, eventually management discovered it was a member of the public who used to nip in unnoticed one day a week, use the toilet and take all the spare toilet rolls in there with him.

Another office, a member of staff used to use the office shower for washing most days. Came with a change of clothes for the work day to use after their morning shower. Wasn’t on a water meter, but wanted to save on the water heating at their home.

> Another office, a member of staff used to use the office shower for washing most days.

We have showers at work, for cyclists, in theory. If you're going to have a shower after getting to work, why would you have a shower at home before cycling to work?

Oh, and definitely shit on company time.

After a series of hard rolls of life’s dice, they got a dream job of selling curios that most of us could never hope to see, to millionaire and billionaires, sometimes joining them for ‘showing them off’ party’s that you and I can only dream of.

As an aside we both once got invited to a party that cost more than a wedding, bagpipes and cannons on arrival, food, fireworks, free bar with the drinks served over a melting ice sculpture, entertainers flown in, fire eaters, free accommodation ect.  The like of which I’ll never attend again. But the party’s he now goes to for work apparently makes that look like a child’s jelly and cake afternoon play date.

last I heard were they were very happy.

Post edited at 22:13
In reply to ScraggyGoat: That's good to hear.

And if you want another twist of life, my former mentor taking the piss on the throne now partly owns his own company with employees…..

Post edited at 22:19

> If you're going to have a shower after getting to work, why would you have a shower at home before cycling to work?

No reason - It was his method of saving energy which is why I mentioned it. Showers were part of the staff facilities available.

> What about efficiency difference of filling from the hot tap rather than cold

Depends on the boiler.

It's almost always more efficient to fill the kettle then to allow the water within to warm to room temperature (mains water is normally colder) before boiling it.

> I always take it from the hot tap but my husband always looks at me like I have 2 heads for doing that!

Vivid memories of fishing rat bones out of the header tank for a hot water system.  Most hot water systems do not reach boiling temperatures and so represent something of a health hazard.  The only reason I'll drink upstairs cold water in my house is because I saw brand new pipes go in all the way from the roadside to the upstairs taps - I'm very suspicious of indoor water in old houses.  The upstairs cold taps here used to come from an open header tank in the loft for reasons I never understood; I think it was there to regulate pressure for the bidets and using it for taps to saved on pipes.  Or they were really worried about washing their bums after the nuclear apocalypse.

> Better stick the kettle on, make an extra cuppa and write to MP's about building standards and upgrading our housing stock.

Well, you could, you know, do both.

> Not far off - specific heat capacity of water is 4200 joules/kg

I think the good captain was quoting in hectojoules/kg, or possibly decijoules/cm3

Edit: Oh, forgot to say, I don't have a kettle, so I guess technically the answer to the op would be "no".

Post edited at 00:10

> It's almost always more efficient to fill the kettle then to allow the water within to warm to room temperature (mains water is normally colder) before boiling it

Depends at which point in the system you are measuring energy efficiency... Are we considering generation & distribution (and the type)? Are we considering how room temperature is maintained? (heating the kettle from the room requires heating the room: what is the efficiency of that?)

It all gets complicated, and very dependent on the specifics of each situation...

Of course, being an untrustworthy microwave user, I use that for making instant coffee; add a splash of milk to the water, nuke it for 1'40", which results in a light crema when you add sugar/coffee, due to the micro bubble nucleation they cause. Like using a steam frother...

My boss has a clever set up out the back of the garage. He has a boiler that's fueled by recycled tyres underneath. At the side is a bowser where old engine oil is kept and drip feeds the fire. We mainly use the set up for steam cleaning but it's a source for our tea from about 10am onwards.

> And if you want another twist of life, my former mentor taking the piss on the throne now partly owns his own company with employees…..

> My boss has a clever set up out the back of the garage. He has a boiler that's fueled by recycled tyres underneath. At the side is a bowser where old engine oil is kept and drip feeds the fire. We mainly use the set up for steam cleaning but it's a source for our tea from about 10am onwards.

Bet the emissions aren't so good.

Best use of old engine oil is treating wood (carefully and away from water courses).  Mix with water, I know it doesn't mix but it acts as a medium and you have to keep stirring. The micro particles of metal act as a deterrent to various boring critters and the oil does what oil does. Way better than any modern day creosote replacement.

Post edited at 08:12

> It all gets complicated, and very dependent on the specifics of each situation...

I was assuming that most of the time a room is unheated.  Then it's very simple.  Gets more complicated as you say in winter.

> Of course, being an untrustworthy microwave user, I use that for making instant coffee; add a splash of milk to the water, nuke it for 1'40", which results in a light crema when you add sugar/coffee, due to the micro bubble nucleation they cause. Like using a steam frother...

Terrifying risk of super-heated water flashing over when you pick it up if you ever guff on the timer...

I make my morning coffe similarly but use any leftover warm water in the kettle, topped up to 150ml -ish plus 100ml of full-fat milk in the cup in the mike. 40 sec nuking the milk, about 30 sec for the kettle, add powder to warm milk and top up with boiled water.

The paralleling of tasks saves nearly a minute, maximum electrical power was 4700 watts for 30 seconds plus another 1600 for 10 seconds overlap. Mike seems to lose 700 watts internally to deliver 900 watts to the cup.

I do this every morning but had not bothered to check the power consumption - and all this before reading your post!

Last night I tried making tea in the cup. 250ml tapwater, bag of Earl Grey into the cold water, 100 sec in mike and stand for 5 minutes. Perfectly drinkable but some unwanted bubbles. 160kJ used. Wrote the post but failed to post it due to Masterchef starting... which reminds me - when a contestant's barely-cooked meat like lamb or duck is obviously too rare, why do they not give it a few seconds in a microwave?

Edit: missing apostrophe

Post edited at 08:22

> Terrifying risk of super-heated water flashing over when you pick it up if you ever guff on the timer...

Vanishingly small risk if you've already put the milk in. Still a great justification for never washing your coffee cup.

I use a microwave for coffee but "the other way". Just enough hot water from the kettle to dissolve the coffee (and sugar), the rest is milk, in the MW for 2 mins to get a frothy latte. Need to keep an eye on it towards the end in case it wants to boil over.

I much prefer my coffee really milky. I blame it on my mother, who used to make me coffee by boiling the milk in a pan and then adding coffee (pre MWs).

As a digression, when dunking, why do biscuits absorb liquid more quickly in watery coffee/tea than in milky coffee?

> Vanishingly small risk if you've already put the milk in. Still a great justification for never washing your coffee cup.

The things I’ve never tried as a non-coffee drinker…

> What about efficiency difference of filling from the hot tap rather than cold? Is it more efficient to have had those first few degrees come from the boiler?

> I always take it from the hot tap but my husband always looks at me like I have 2 heads for doing that!

I am also of the generation that is pre-programmed not to drink from the hot tap - or even the upstairs cold taps!

In our house, if I want cold water for squash, I'll get it from the utility room, which is closest to where the water comes into the house and therefore is the coldest.

For everything else, we use the kitchen tap - water there has run through part of the house and that's warmed it up a bit, so the kettle has a bit less work to do.

I can remember the skin that forms when pan-boiled milk is used - great with custard but hate finding it in coffee...

congratulations on the thread that has the biggest interest gap between its apparently mundane title and the fascinating posts

When I was a nipper our hot water came from the back boiler behind the fire. This was made of lead and the pipes also. ‘Thal get lead posinin’ if tha drinks from hot tap”  I was always told. It used to be my job to get the fire going in a morning. No fire no bath.   Wow this is bringing back some memories 😁

Hold up .....

You can't compare a quooker to a kettle simply on a cost-per-cup basis.  You need to factor in the cost of the device.

A quooker will set you back £700 + installation.

Is a quooker cheaper simply on a cost-per-cup basis excluding device cost + installation ... maybe/debatable.  Quooker will certainly try to tell you that they are.  If it is cheaper - we're talking fractions of pennies.  No one is going to save the planet by using a quooker over a half filled kettle.

A reasonable kettle out of tesco will set you back £20 and likely have a similar life span to a quooker. (10 years each?)

With £700 (min) cost + installation ... there is, IMO, ~0% chance that the cost-per-cup, inc device cost, is comparable between a quooker and kettle unless you are buying an exceptionally expensive kettle or your quooker has an exceptionally long maintenance free life span - say 30(?) years.

That all being said ... i think the instant hot water taps are fantastic.  They are inevitably the future if only for the convenience factor.

Post edited at 09:36

> Apparently stove top kettles are most efficient

This surprises me greatly. I would have thought an electric kettle would “scatter” (technical term I’ve just invented) much less heat than a kettle on a hob, gas or electric. Using a kettle on a gas flame must be very inefficient judging by how much hot air comes up the sides of the kettle. Warms your kitchen though. My electric kettle doesn’t get warm at the bottom where the element is but the sides slowly get warm presumably by conduction from the water, so in terms of energy in and energy out must be very efficient.

No one mentioned using a microwave to heat and the efficiency or not of using one

> You can't compare a quooker to a kettle

Unless a Qooker is different to the hot/cold dispenser taps in the kitchenettes at work, it will keep a hot reservoir going all the time; and a chiller. I don't think they do a genuine, on demand heat/chill action.

Anything running continuously, with a low demand cycle, is going to knock the efficiency.

Yes, I was just thinking this is an example of how a lot of UKC threads manage to start in one place and morph into something very different and wide ranging. I think it’s a testament to the large number of intelligent and thoughtful people who frequent these forums (not including myself, for modesty’s sake).
on a slightly different tack, I have noticed that, on an issue like this one, different folk think along different lines. In particular, some people are thinking about saving money rather more than looking at the global need to minimise energy waste. Some people (not just UKC habituees) don’t worry about wasting energy or anything else if they personally aren’t picking up the tab. Example is having shower at work, or not bothering to switch off lights there.

> No one mentioned using a microwave to heat and the efficiency or not of using one

I noticed that too. In terms of efficiency (not speed) mw should to my way of thinking waste less heat as all the energy goes into the liquid. Unless anyone says different. But mw, mine anyway, is much slower than kettle.

We have an alternative, but (I think?) equally efficient method.  We often fill the kettle here.

- Can the clever folks tell me if it is a good way IF you invest in a good thermos?

We usually boil enough for the drinks we want plus enough  excess to fill a large good quality thermos  This keeps the water hot enough for us for the day or however long the hot water lasts)  If your favourite beverage requires absolutely boiling water, then use the very hot water from the thermos to reboil it.   We very rarely need to do that.

I thought quooker must be a mis-spelling of cooker, but apparently not.

Unless your thermos has 100% insulation it must squander some heat during the day, and for this to be equally efficient there would need to be an advantage in heating water in bulk rather than in two or more separate sessions. Perhaps several separate boilings would save a little as you are only starting with a cold kettle the once. This really is getting picky! 😀

> Using a kettle on a gas flame must be very inefficient judging by how much hot air comes up the sides of the kettle.

It all depends on where you measure the efficiency.  If you count energy coming into the house then an electric kettle will be more efficient than gas because, as you say, some of the heat of the gas is lost to the air.

But the production of the electricity (assuming from a CCGT) is not perfectly efficient; they achieve around 60%.  And then there are transmission losses.  So, on the back of a fag packet, I'd suggest that the actual amount of gas burned to heat your water is likely to be fairly similar either way.

Agreed ... definitely not equally efficient if you ever reboil the water!

> We usually boil enough for the drinks we want plus enough  excess to fill a large good quality thermos  This keeps the water hot enough for us for the day or however long the hot water lasts

So you're saving energy in two ways here.  You aren't repeatedly boiling too much water, because you presumably take exactly the right amount of water from the thermos each time you make a drink (as opposed to always boiling a small amount too much in the kettle).  This effect is going to be somewhere between negligible (if you are super accurate every time you fill the kettle) and quite significant (if you are very lazy and always overfill your kettle).

Secondly, you're not heating the kettle up multiple times a day - the energy used to raise the temp of the kettle itself is wasted each time.  Is this significant?  Metal has a very low heat capacity (steel is ~10% of water) so if you're using a metal kettle, probably fairly insignificant.  Heating up 500g of steel in a kettle body is like 50g of excess water.  Plastics have higher capacities (~30% of that of water) so perhaps more significant.

I would hazard a guess that if you make lots and lots of small drinks, and can't be bothered to accurately measure the water into the kettle each time, then the thermos might be measurable better.  If you make a few big rounds of drinks, probably not worth the bother.

> Of course, being an untrustworthy microwave user, I use that for making instant coffee; add a splash of milk to the water, nuke it for 1'40", which results in a light crema when you add sugar/coffee, due to the micro bubble nucleation they cause. Like using a steam frother...

That... is not coffee!!

> That... is not coffee!!

It's decaf, too. And I'm currently using up some shit Nescafe Gold Blend stuff I bought on offer. Smells like shit. Should have taken it back.

I'm not a coffee snob. It's just a warm drink.

Thread reminds me of an argument I had many years ago on here.

If the power of all electric kettle heating elements were lowered, both the day-time instantaneous and time-averaged power draw across the UK go up.

One kettle: Lower power > takes longer to boil a kettle > more thermal and evaporative losses to the environment > increase in energy lost > increase in total energy used.

Big picture:  Thousands of kettles are on at any one moment; decrease individual power and this number goes up (as each kettle on for longer, more overlap) with the  increased energy loss being reapplied as even more kettles on at once.

Statistical mechanics.

Seems to me the biggest ways to save energy with a kettle are more insulation and perhaps a pressure system to prevent evaporation - that's another point in favour of boiling water taps, although their cost and complexity remains orders of magnitude beyond a tap, assuming someone has a boiler for other purposes.

> I have noticed that, on an issue like this one, different folk think along different lines. In particular, some people are thinking about saving money rather more than looking at the global need to minimise energy waste. Some people (not just UKC habituees) don’t worry about wasting energy or anything else if they personally aren’t picking up the tab. Example is having shower at work, or not bothering to switch off lights there.

Thinking about the work shower thing just now, is it that clear cut or much more nuanced?

Could it not be that showering at work for some could be a positive way in minimising wasting energy? A lot of offices, and not just office building (climbing centre!), past and present, have heating and stored/pumped hot water on 24/7, or more or less, whereas a person could be living alone and not having any hot water switched on normally. I would guess there would be minimal extra energy used by showering in the office running 24/7 system c/w heating up say a hot water tank from cold for a shower a home?

Re not switching lights off, I’ve noticed since LED lights have been more and more available, a significant increase in houses using outside eave lights and some on dusk to dawn sensors. My electrician said to me most of them that he does are for aesthetic reasons and when one house gets them many nearby copy.

Last night I walk past a house which had 18 outside eave lights (plus two for the front/back doors which seemed superfluous to me but also on), but I’ve previously seen others with 20 and more. Even with the increased efficiency of LEDs there must be an increase in electricity being used overall?; in the past I guess old school thinking was it costs money so switch it off when you don’t need it, and outside lights were more for practical reasons.

It’s going to take along time for some to give thought to the whole matter of reducing energy use.

>If the power of all electric kettle heating elements were lowered, both the day-time instantaneous and time-averaged power draw across the UK go up. <

I seem to remember there was a proposed maximum 2kW element in new kettles (EU directive?),

My first thoughts were to agree with you, but 2kW elements might save power since many people boil excess water. They would be less likely to do so if they had to wait roughly half as long again for the kettle to boil compared with a 3kW (might also be more likely to miss a bit of a TV programme after an advert break).

> If the power of all electric kettle heating elements were lowered, both the day-time instantaneous and time-averaged power draw across the UK go up.

Yes, absolutely.  The most efficient kettle would be very high powered.  As long as we're not talking about increasing the flow to a gas hob and more heat energy just gets pushed out the sides.  My largest gas hob is actually a little quicker if you turn it down to about 90% because at full blast lots of gas goes up the sides of the kettle.

> Seems to me the biggest ways to save energy with a kettle are more insulation

Would convective and radiative losses through the body of the kettle be that significant?  I'd have thought a way to measure exactly the right amount of water would be more effective.

> and perhaps a pressure system to prevent evaporation

I tried to design something like this for my GCSE DT practical assessment.  I got quite a long way down the line before my teacher told me he was uncomfortable with the risk of an exploding can of boiling water in his classroom.  I ended up making a shelf with a little safety guard instead.

LED is about ten to twelve times as efficient as incandescent (around 50% versus 4%).  If switching from incandescents to LED also causes a behaviour change to leave the lights on for ten times as long (or to use ten times as many) then we're back where we started.

I have to admit I am less religious about switching lights off around the house now that I know they're burning 8W rather than 100W!

> I seem to remember there was a proposed maximum 2kW element in new kettles (EU directive?),

Oddly enough, that was a Daily Mail lie.

Jetboil Roolz all the way.

Only heat what you need, a former colleague was obsessed with filling the kettle to the brim to make one or two cups of tea. Initially hoped it was intentional to wind me up a bit but no, sadly not...

On a similar note years ago someone showed me how to cook rice as they do in parts of the world where fuel and water are hard to come by. Just enough water to cover the rice, bring it to the boil and leave for a minute or so. Then turn the heat off, put the lid on the pan and leave for 15 minutes. Much better than pointlessly boiling a near full pan of water.

> You might be better having a 2 minute timer in your shower.  Saves far more energy.

Timed my normal shower this morning. Two and a half minutes.

I'd never even heard of not drinking from upstairs taps!! Funny, I don't consider myself particularly young but in this conversation I feel like I am a different generation to many on here! lol

> Seems to me the biggest ways to save energy with a kettle are more insulation and perhaps a pressure system to prevent evaporation - that's another point in favour of boiling water taps, although their cost and complexity remains orders of magnitude beyond a tap, assuming someone has a boiler for other purposes.

Or for a more radical energy saving, how about everyone stops drinking several hot drinks every day?

> I have to admit I am less religious about switching lights off around the house now that I know they're burning 8W rather than 100W!

That maybe part of the thinking when folk install led generally possibly? It’s only x watts nowadays so minimal electricity type of thinking. However, what appears to be a trend of having lots of outside lights (additional never there before) just for aesthetic reasons is just adding to the waste of energy. Some are so bright there is no need for the street lights nearby!

I don’t have as much concern with lights being left on where there is a need for whatever reason and less so when they are LEDs (I’m guilty of having some background lights on for longer for safety and security lights for example).

Post edited at 13:07

> on a slightly different tack, I have noticed that, on an issue like this one, different folk think along different lines. In particular, some people are thinking about saving money rather more than looking at the global need to minimise energy waste.

A more relevant metric, in these times, is the saving on greenhouse gas emissions rather than energy. Where energy generation is concerned that largely means saving on carbon dioxide emissions. For kettles, that means using as little electricity each as possible each time you use it, or reducing as far as possible the carbon intensity of that electricity. Not that most of us have much of a choice about that. For a kettle using grid electricity, the emission from manufacture and disposal are currently much smaller than the in-use emissions. So follow all the tips given here for capping those.

The less carbon intensive the electricity supply becomes, the more the balance shifts towards the manufacture  and disposal parts of a kettle's life cycle. It's the same with buildings.

>  However, what appears to be a trend of having lots of outside lights (additional never there before) just for aesthetic reasons is just adding to the waste of energy. Some are so bright there is no need for the street lights nearby!

Plus many of them are uplighters adding to light pollution .

Maybe much of the microwave energy ends up in the liquid, bit only 70% (?) of the electricity ends up as microwaves. The rest heats up the oven gubbins. vs electric kettle where all the electricity ends is as heat and only some of it into the water.

> Maybe much of the microwave energy ends up in the liquid, bit only 70% (?) of the electricity ends up as microwaves. The rest heats up the oven gubbins. vs electric kettle where all the electricity ends is as heat and only some of it into the water.

Had full nest of crows mother and babies in ours years ago., well rotted!

> This surprises me greatly. I would have thought an electric kettle would “scatter” (technical term I’ve just invented) much less heat than a kettle on a hob, gas or electric. Using a kettle on a gas flame must be very inefficient judging by how much hot air comes up the sides of the kettle. Warms your kitchen though. My electric kettle doesn’t get warm at the bottom where the element is but the sides slowly get warm presumably by conduction from the water, so in terms of energy in and energy out must be very efficient.

You echo my thoughts, but I've absorbed it from a few different places as being more efficient. Perhaps some googling is in order to see if it's more of a common myth.

> No one mentioned using a microwave to heat and the efficiency or not of using one

Well...

https://www.ukclimbing.com/forums/off_belay/do_you_fill_your_kettle-741443?v=1#x9551790

Electric kettles are really very efficient (at point of use) at converting input electrical energy to thermal energy; the only inefficiencies are in heating the element and kettle, and losses from the kettle during the short heating cycle. As suggested above, the smaller the volume of water, the lower the efficiency, as there is relatively more kettle to heat.

A microwave oven is significantly less efficient at converting input electrical energy to thermal energy, due to the losses in the cavity magnetron and the power supply. One has to hope that the RF power generated by the magnetron ends up in what is being cooked...

petemeads provided some estimates of microwave losses; 700W loss for 900W delivered ~56% efficient.

https://www.ukclimbing.com/forums/off_belay/do_you_fill_your_kettle-741443?v=1#x9551820

Post edited at 19:05

> Terrifying risk of super-heated water flashing over when you pick it up if you ever guff on the timer...

As alluded to above, my earthenware coffee cups aren't so clean as to allow water to get that superheated without boiling. And I'd notice if I messed the timer up that much; I have a favourite set to bring a cup of water hot enough, but nowhere near boiling.

I'm parched. Anyone fancy a brew?

Well I got bored, Mrs is watching celebrities playing with sheep balls or something, so I timed the kettle (2.5 - 3 kW) to boil a cup of water = 61 seconds

Microwave (900w) takes 120 seconds.

Also the microwave only heats the water and the cup for the programmed time, but the kettle heats the element and the kettle body itself, plus it takes a while for the bimetallic strip to get hot enough to switch it off.

The above results indicate the microwave may actually be more efficient.

Hope you didn’t pour the hot water down the drain.

Do I fill my kettle?!

No but I do have the windows and doors open because the central heating and wood burner make it too hot 😁

We’ve all been thinking it.

No electric kettle boiling here tonight; power is out for 20 miles in most directions and the weather is worsening.  Lights are on in wintertree towers but I doubt the batteries will get much charge from the solar tomorrow so the stove top kettle is coming out…

>  Lights are on in wintertree towers but I doubt the batteries will get much charge from the solar tomorrow so the stove top kettle is coming out…