Boiling kettles and only using enough water - is this REALLY a big issue?

[MrsSeanBean]

This is a genuine question.

I find it hard to judge exactly how much water I will need, and added to that, I live in a hard water area and find it difficult to keep the bottom of my kettle free of scale.

I am not saying that I always fill to the brim to boil for one cup/ mug of coffee - but how much difference will it really make if I boil - say - 300ml when I only need 200ml? How much energy am I saving?

It struck me today that it must surely be fairly neglible in the grand scheme of things, and yet you always see it in lists of green tips. I would have thought, walking, line drying, composting, turning off lights and TV etc would be more worthy of promotion (although those things are sometimes promoted as well - it's just that the kettle one seems very prominent and maybe out of proportion to the potential energy saving benefits).

To be honest, it's big businesses and manufacturers that produce the most carbon dioxide, not the average house. It sounds like you are doing loads already, if we were all doing the same it would make a difference but businesses are the major polluters. A little bit of energy to boil a kettle won't make much of a difference.

It's because say every household boiled their kettles twice a day - is the population about 60 mil? So that's 120mil kettles boiled a day. It's the cumulative effect. And it's so easy with no affect (to yourself).

LoW - yes there must be a lot of kettles I agree. But I am interested if anyone knows exactly the energy (kilowattage or however it is measured) that is saved per boiling of 100ml of liquid, as opposed to say 30 million TVs being turned off stand-by overnight.

There was something a few years back (an advert) that said if everyone just boiled the water they used in X time you could light up a big city for a certain time. Cannot remember the details excatly. I am sure it's not as big a 'saving' as lights off/no standby/heating lower but someone doing just that is probably better than nothing at all, which is why they mention it I guess.

Yes, maybe it is used as a tip because it is something really basic/ easy and which 99% of people probably do several times a day.

Interestingly the saving is more in summer than in winter. This is because in winter if your kettle is in a room with thermostatically controlled central heating then the heat from the extra water will dissipate out and heat the room (assuming you don't pour the surplus down the drain) and hence save you a small amout of heat energy from your central heating. Now admittedly, electricity is a less efficient method of heating than gas, but it's not that much less efficient, so in winter, by boiling extra water all you are really doing is heating your house in a different way. Same with leaving lights on as well - all that energy gets turned to heat too.

We've invested in an OWL monitor - it tells you how much electricity is being used at any one time.

This made me see clearly why overfilling the kettle is a VERY BAD THING - the monitor shoots up when the kettle is on.

Obviously if there's less water, it boils quickly so doesn't consume as much power and therefore costs less.

Other baddies are: the electric oven (until it reaches temperature), and as you'd expect, the washing machine and dishwasher.

It also makes a big difference if lights are on in rooms with lots of bulbs...but the kettle is the one that really stands out.

How much did you spend for the monitor/. and where did you get it?

I went to an ethical- and eco-themed talk last week, and the statistic quoted there was that boiling one mug of water takes the same amount of energy required to power an average low-energy light bulb for seven hours. If this is true, I can see that - if everyone took this sort of advice on board (boiling less water, lights off, things off standby, etc) - this kind of thing would help at least a bit. And, like another poster said, for very little effort. Homes are directly responsible for 20-30% of carbon dioxide emissions, so we can definitely do some reducing. And that's before looking at our transport contribution.

We also have one of those real-time electricity usage monitors, which calculates overall electricity usage - and which you can use to work out individual appliances' usage by switching things on and off and looking at the display. Kettles really do use a lot of energy (I just tested ours, with one mug of water in it, and it added over 2.5KW to 444W of evening activity in a four-bedroom house). If you can keep your kettle on for less time by boiling only what you need, it helps - a little bit. Isn't it the principle of it, too?

We live in a hard water area too. Sling a bottle of cheap vinegar in your kettle overnight every now and then to get rid of the limescale. My mum uses one of those wire ball things - don't know if they're any good?

Lenlen, Eco-eye and Efergy monitors were recommended to me. You can get them here. HTH.

We have an eco kettle. It has a water reservoir so you dont have to constantly refill it and it boils extra fast. I love it (but no guests can ever work out how to use it) only downside is their 1 cup marker needs to be 1 and a half for our big cups but once you have worked that out its fine.

You could figure out the difference by

a) putting 1 cup of water in the kettle and timing how long it takes to boil (time x)

b) putting 2 cups of water (at the same starting temp) in the kettle and repeating (time y)

c) taking (time y) - (time x) will give you the additional running time for boiling the extra water = time z.

d) look at the wattage of your kettle - say it is 2 kw and time z = 2 minutes then the additional energy used is 0.67 kWh or 0.67 of a minute (if my maths is right - I calculated 2 / 60 x 2 )

which would light a 15 W energy saving lightbulb for approx 4 hours.

I bet my sums are wrong but you see the principle of the thing. Strikes me as an ideal educational experience for a small child to work out

MrsSeanBean - first of all I am sure you are doing a lot already to save energy and you should not worry too much about this.

I have worked in the energy industry and for me the important thing is not wasting energy from a purely economic standpoint. I do try and boil as little water as possible when I boil the kettle - to save money. However, it really is impossible to be exactly accurate about precisely how much water you need without going to great lengths and is not practical in day to day life.

I feel boiling 100 ml extra of water is not a crime. However, I tend to boil a very small amount when I just need say 2 cups of coffee and never boil a full kettle unless I really know I am really going to use it all.

Remember also the heat in the unused water in your kettle will dissipate into the atmosphere in your home. Even if you boil a bit too much water, that heat dissipating into the atmosphere does help to heat your home so it is not totally 'wasted' in the strict sense as you are enjoying heat from the kettle that would otherwise have to be produced by your heating system.

It is the same with low energy bulbs. The main energy saving is they do not produce as much heat as a normal bulb. However, as they produce less heat you will have to replace that lower heat production from your low energy bulbs with an extra bit of heat from your boiler and heating system. Hence the energy saved by a low energy bulb is not all 'saved' if you have to turn your boiler on that bit longer to generate a bit more heat for your home.

Almost all environmental issues have these complex tradeoffs within them but are poorly explained by Govt and other environmental interest groups.

Betadad - yes, true about the heat - but surely that is only a valid argument if you heat your home with electric bar / storage heaters.

Otherwise, you are turning gas (or coal or whatever) into electricity, at an efficiency of say 60% for a new shiny gas power station (and losing the remainder as heat up cooling towers & into the sea), and then back into heat at your house.

If you have a gas boiler (particularly a modern condensing boiler that can turn say 80% + of the energy in the gas into usable heat in your home) it appears to make more sense to use the electricity for jobs that only electricity can do (light, for example) and heat your home with the gas directly.

Sorry, forgot to say, not much point of course in worrying about the odd cup of water and then flying to Benidorm for your holidays!

Takver - yes' you are right and that makes the 'trade offs even more complex to calculate for the layman.

You are right about flying as well. People flying to international conferences on climate change is an irony too far for me.

MrsSeanBean - you need to get (or download for free ) this book - Sustainable Energy Without the Hot Air by David Mackay. He does the sums and gives you answers to this kind of question.

I agree 100% that the lists of energy saving tips are often bizarrely out of proportion to the amount saved. One of Mackay's favourite examples is that the amount you save by always unplugging your mobile phone charger when you're not using it, for a whole year, is the same as that used by taking a single hot bath.

(I love baths. Am eco-criminal )

On the subject of boiling water and saving energy can I ask a question.....

If you need to bring a pan of water to the boil before you add, for example, pasta is it more fuel efficient to-

-boil the water in a kettle and add it to the pan

-or boil it in the pan on the gas hob?

by "-or boil it in the pan on the gas hob?" I obviously mean bring it to the boil on the gas hob

I have the same problem mrsseanbean. I find if I boil the exact amount for a small cafetiere, then the last bit I pour out has horrid limescaley lumps in it.

kathy have you also read the CAT 'Zero Carbon Britain' report? (available as pdf from here ) - I thought that the Mackay book was interesting but that he was far less apolitical about it than he claimed. He is rather inclined IMO to

(a) be very specific on the numbers in most cases but then elide gracefully over difficult point that don't suit his argument
(b) assume that no behaviour change is possible except where it is a change that he is comfortable with, at which point he assumes that everyone will follow it automatically.

I think that the Zero Carbon Britain report is not necessarily better, but a good thing to read in combination with it, as I think they do a good job of tackling things that he doesn't really deal with, and I liked the fact that they set up an explicit plan of action in the different areas of the economy that one could then agree or disagree with IYSWIM.

Heating 1ml of water by 1 degree C takes 1 calorie. If we assume that the water comes out of the tap at 15C (for sake of argument), raising 100ml to 100 degrees (ie boiling it) will take 85 x 100 calories = 0.01 kWh.

So boiling 100ml of water takes one hundredth of a 'unit'. That's the same amount of energy that a single 60W bulb uses in 10 minutes.

I keep a flask by the kettle and pour any excess into it. Then if I need a little hot water for cooking, or to rinse a pot I have some nearly boiling water to hand. It saves a lot of water as our water takes ages to run hot.