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• FIRST POST
• bikerchris
• 12th Oct 12, 3:46 PM
• 153Posts
• 106Thanks
bikerchris
This seems a little sad, but while I was recovering from an evil RTA, I had plenty of time on my hands. I had an old kettle (the type that has an exposed coil) and wondered if it was cheaper to boil water for a coffee/tea on the gas hob. I then bought a modern kettle (internal hot plate type) later on because the original went pop. I did check MSE and there was only claims and no evidence (although the guesses were pretty believable).

So here's the results. Appreciate that I'm not that technical and just tried my best to get it roughly useful:

ELECTRIC:
Kettle type 1 (exposed coil, this meant more water was necessary to cover the element): Energy used: 0.057Kwh (revised, thanks rogerblack)
Kettle type 2 (hot plate type, so precise amount of water for one 'proper' cup): Enegery used: 0.036kwh (revised, thanks rogerblack)

Kettle type 1: 0.57 x 12.67 = 0.72pence (revised, thanks rogerblack)
Kettle type 2: 0.36 x 12.67 = 0.46pence (revised, thanks rogerblack)

GAS:
This is more complicated because of the way gas usage is calculated. I didn't have a stove kettle, so I used a small saucepan with a lid over instead.

Gas used: 0.03 cubic feet

To convert to charged units:

0.03 x 100 x 1.02265 ("Correction factor") = 3.06795

3.06795 x 0.283 ("Conversion factor") = 0.086822985

0.086822985 x 39 ("Calorific Value") / 3.6 ("Conversion factor") = 0.9405823375

So gas used is: 0.94

Gas units are: 8.61pence each

ACTUAL COST: 8.0984 pence.

Perhaps not that interesting, but it'll save someone some boring time. Do say if you think I've got something wrong, no ones perfect! To calculate the power used, I used the plug in meter type. To measure gas I read directly from the meter (gas is not used to heat the property, only the cooker). Prices include VAT but not a portion of any standing charge. I'm officially the sadest person in the world
Last edited by bikerchris; 13-10-2012 at 1:39 PM. Reason: Wrongly calculated - thanks to rogerblack
If someone is worth thanking - click on the 'Thanks' button on their response. It's just a nice thing to do :-)

Started debt at 17, stopped by 25 :-D ...I'm in debt again because of property :-/
Page 1
• rogerblack
• 12th Oct 12, 4:33 PM
• 9,274 Posts
• 9,438 Thanks
rogerblack
Naah - I'm actually making myself an energy efficient kettle.
That beats just measuring.

One thing to note.
'Concealed element' kettles generally have a plate, onto which is bolted a conventional 'wiggly' element.
This means a considerable extra mass of stuff to heat.

It's quite easy to see how much or little you can safely put in a kettle.
When underfilled, part of the element will get very hot, and you will see rapid boiling at the edge of the water.
All kettles of the wiggly element type that I've come across actually do not heat the 'ends' of the element, where they rise up to meet the body of the kettle.

Also, I suspect you may have mis-measured.
0.36 units, if using a 2000W kettle is 0.18 hours, or about 10 minutes.
This seems rather excessive, and is enough energy to boil from 20C over 3 litres of water.
Are you sure it wasn't 0.036?
• Cardew
• By Cardew 12th Oct 12, 4:43 PM
• 27,706 Posts
• 13,597 Thanks
Cardew
This seems a little sad, but while I was recovering from an evil RTA, I had plenty of time on my hands. I had an old kettle (the type that has an exposed coil) and wondered if it was cheaper to boil water for a coffee/tea on the gas hob. I then bought a modern kettle (internal hot plate type) later on because the original went pop. I did check MSE and there was only claims and no evidence (although the guesses were pretty believable).

So here's the results. Appreciate that I'm not that technical and just tried my best to get it roughly useful:

ELECTRIC:
Kettle type 1 (exposed coil, this meant more water was necessary to cover the element): Energy used: 0.57Kwh
Kettle type 2 (hot plate type, so precise amount of water for one 'proper' cup): Enegery used: 0.36kwh

Kettle type 1: 0.57 x 12.67 = 7.22pence
Kettle type 2: 0.36 x 12.67 = 4.56pence

GAS:
This is more complicated because of the way gas usage is calculated. I didn't have a stove kettle, so I used a small saucepan with a lid over instead.

Gas used: 0.03 cubic feet

To convert to charged units:

0.03 x 100 x 1.02265 ("Correction factor") = 3.06795

3.06795 x 0.283 ("Conversion factor") = 0.086822985

0.086822985 x 39 ("Calorific Value") / 3.6 ("Conversion factor") = 0.9405823375

So gas used is: 0.94

Gas units are: 8.61pence each

ACTUAL COST: 8.0984 pence.

Perhaps not that interesting, but it'll save someone some boring time. Do say if you think I've got something wrong, no ones perfect! To calculate the power used, I used the plug in meter type. To measure gas I read directly from the meter (gas is not used to heat the property, only the cooker). Prices include VAT but not a portion of any standing charge. I'm officially the sadest person in the world
Originally posted by bikerchris
I am even sadder to correct you!

You are not comparing like with like.

1. You are using the Tier 2 kWh price for electricity(12.67p/kWh) but the Tier 1 price for gas(8.61p/kWh). The tier 2 price for gas is around 3.5p/kWh)

2. A gas unit on an Imperial gas meter is 100 cubic feet, so I suggest you are using 3 cubic feet not 0.03 cubic feet. A gas unit is approx 33kWh so 3 cubic feet would be approx 1kWh(you made it 0.94kWh)

3. I believe your measurements of electricity used are completely wrong(probably by a factor of 10). For 1 litre of water (i.e. 4 cups) from tap temp to boiling, my kettle uses 0.10kWh so 4 cups cost 1.27pence(using your price) so around 0.3p a cup.

4. Similarly whilst I don't have a gas hob, I don't believe that a gas hob will use 0.94kWh for a single cup. about 30 times more than electric.
• Pincher
• By Pincher 12th Oct 12, 5:14 PM
• 6,516 Posts
• 2,491 Thanks
Pincher
Gas units are: 8.61pence each
Originally posted by bikerchris
I'm paying 3.2 pence per kWh for gas, or about £1 per imperial unit.

The gas example is flawed, as you have to heat the whole kettle up first.

This is actually quite a good Richard Hammond segment, but I would say use six different approaches for one cup of tea, 2, 3 and 4 cups of tea. We need the time to boil as well.

If we are using 3kW kettles, then the gas burner should be 3kW as well.

Gas

Kettle with whistle.

Electric

1. Electric exposed coil

2. Electric concealed coil

3. Microwave, 800W Magnetron.

4. In-Sink-Erator HC-1100 hot water dispenser, which claims 98 degrees, with microwave to bring it to boil.

5. Quooker, which claims 100 degrees, so no need to microwave.

I assume Quooker keeps a small tank at 95 degrees, and heat the flowing water to boil as it flows out.

Without doing the experiment, I expect the microwave to be the winner for being the cheapest for one cup of tea, but slowest, because it is only 800W.

The Quooker should be the fast draw in the west of course.
• Cardew
• By Cardew 12th Oct 12, 5:23 PM
• 27,706 Posts
• 13,597 Thanks
Cardew
[QUOTE=Pincher;56482513]
3. Microwave, 800W Magnetron.

Without doing the experiment, I expect the microwave to be the winner for being the cheapest for one cup of tea, but slowest, because it is only 800W.

QUOTE]

Don't forget that the 800watt rating of a microwave is the magnatron output; the appliance consumes a lot more power than 800watts.
• Cardew
• By Cardew 12th Oct 12, 5:47 PM
• 27,706 Posts
• 13,597 Thanks
Cardew
In all of these comparisons of costings, it is easy to forget the Laws of Thermodynamics which state that energy cannot be created or destroyed.

Using, say 1 kWh of electricity for any purpose produces heat. So that 1kWh for heating kettles(gas or electric) produces heat for the fabric of the house which, for at least the winter months, is one less kWh needed from a conventional heater.

My PC setup uses around 200watts, but that is 200watts less I need to heat my study.
• thor
• By thor 12th Oct 12, 7:48 PM
• 5,275 Posts
• 1,889 Thanks
thor
In all of these comparisons of costings, it is easy to forget the Laws of Thermodynamics which state that energy cannot be created or destroyed.

Using, say 1 kWh of electricity for any purpose produces heat. So that 1kWh for heating kettles(gas or electric) produces heat for the fabric of the house which, for at least the winter months, is one less kWh needed from a conventional heater.

My PC setup uses around 200watts, but that is 200watts less I need to heat my study.
Originally posted by Cardew
That is a bit simplistic. To be more accurate you cannot say that a 1KWh heater produes 1KW per hour of heat energy. The same can be said for your 200W PC. Both also dissipate the energy mechanically and audibly.
• Fred Bear
• 12th Oct 12, 9:31 PM
• 393 Posts
• 192 Thanks
Fred Bear

ELECTRIC:
Kettle type 1 (exposed coil, this meant more water was necessary to cover the element): Energy used: 0.57Kwh
Kettle type 2 (hot plate type, so precise amount of water for one 'proper' cup): Enegery used: 0.36kwh

Kettle type 1: 0.57 x 12.67 = 7.22pence
Kettle type 2: 0.36 x 12.67 = 4.56pence

I'm officially the saddest person in the world
Originally posted by bikerchris
Sorry bikerchris but I am even sadder than you so you can't be world champ.

I don't have any figures for gas, but I know a lot of heat escapes into the air - useful in the winter but wasted in the summer.
Electricity: I have carried out numerous experiments in my laboratory and here are the results for boiling 250ml (1 mug):

Kettle: Morphy Richards Perfection 436732 with temperature display and concealed element:
Manually switching off at the earliest possible point while still achieving 100deg 0.027kWh cost 0.34p
Leaving the kettle to switch off automatically 0.043kWh cost 0.54p

Microwave: Sanyo EMS1552 (900W output, 1420W input)
Boiling in the mug: 0.068kWh cost 0.86p

HTH Fred Bear

So that's why he takes so long to make the tea!
Oh and it isn't his laboratory, it's my kitchen.
- Mrs Bear
Last edited by Fred Bear; 13-10-2012 at 12:25 AM. Reason: To add microwave input details
• Cardew
• By Cardew 12th Oct 12, 10:26 PM
• 27,706 Posts
• 13,597 Thanks
Cardew
That is a bit simplistic. To be more accurate you cannot say that a 1KWh heater produes 1KW per hour of heat energy. The same can be said for your 200W PC. Both also dissipate the energy mechanically and audibly.
Originally posted by thor
Firstly no such thing as a 1kWh heater.

However a 1kW heater running for an hour will use 1kWh of electricity and all(100%) of that electricity will be converted into heat. Even if it has a fan.

What happens to the energy used to rotate the fan? Some will be used to overcome the friction in the bearings (generating heat here), and some will be used to
move air, and when the air slows down due to
its viscosity, the energy again gets turned into heat which warms the air. Add it all up, and you'll find the amount of heat created by a heater exactly matches the energy input into it. (That applies not only to heaters, but all electrical
devices - they all produce heat equal to the energy consumed, but hopefully do something useful before the heat release).
My computer consuming 200watts, even with the loudspeakers on, the hard drive operating etc will still be(eventually) converting that energy into heat.

You cannot destroy energy.
• Pincher
• By Pincher 13th Oct 12, 12:01 AM
• 6,516 Posts
• 2,491 Thanks
Pincher
[QUOTE=Cardew;56482777Don't forget that the 800watt rating of a microwave is the magnatron output; the appliance consumes a lot more power than 800watts.[/QUOTE]

Yes, always correct for the nominal factor.

Peter Ustinov, can't remember the movie.
• rogerblack
• 13th Oct 12, 12:22 AM
• 9,274 Posts
• 9,438 Thanks
rogerblack
Yes, always correct for the nominal factor.

Peter Ustinov, can't remember the movie.
Originally posted by Pincher

It can be rather more than nominal.
Often it's more like 50%.
• missile
• By missile 13th Oct 12, 5:01 AM
• 9,943 Posts
• 5,040 Thanks
missile
I recently had installed a http://www.iconappliances.co.uk/index.php?target=manufacturers&manufacturer_id=61

No idea how efficient it is, but it is convenient.
"A nation's greatness is measured by how it treats its weakest members." ~ Mahatma Gandhi
Ride hard or stay home
• bikerchris
• 13th Oct 12, 1:50 PM
• 153 Posts
• 106 Thanks
bikerchris
rogerblack - thank you for pointing out my mis-measurement - must have been the painkillers Have corrected though. Thanks for the wiggly info too

Cardew - Glad someone is sadder than me! You are right, in my situation though, I seldom use a whole unit of gas, so it's kinda more applicable in my situation to someone that uses gas to heat and goes over the tier threshold. Does that sound fair?

The gas measurement was taken from a gas meter that seems to indicate a decimal after 4 units. So I just figured that I was measuring to 2 decimal points, which was 3. You'll see I was wrong about the 'lecky and have corrected it.

May be I should double check the gas meter though

Fred bear - you win hands down I shall hunt down your findings in future, if I need to know anything! Thanks for the detail, very interesting indeed and a worthy thank you

It seems there was some heated discussion as a result of my admitedly crap 'test'. But I'm grateful to all for not doing what sometimes happens on forums - kicking a person down when they're wrong. Thanks to everyone for not just having the correct information, but for letting me know in a friendly way, really kind of you.

Time for a cup of tea I think, it's now more pleasurable because I'm no longer p**sing into a bag
If someone is worth thanking - click on the 'Thanks' button on their response. It's just a nice thing to do :-)

Started debt at 17, stopped by 25 :-D ...I'm in debt again because of property :-/
• hypnosisderby
• 5th Jan 13, 6:54 PM
• 17 Posts
• 0 Thanks
hypnosisderby
So, despite some people saying you didnt test this scientifically well enough ! is it still right that electricity is the cheapest way to heat a small amount of water? Even if you didnt test to this or that standard, you cant have been that far out on the results??

thanks
Last edited by hypnosisderby; 05-01-2013 at 6:57 PM.
• Cardew
• By Cardew 5th Jan 13, 8:05 PM
• 27,706 Posts
• 13,597 Thanks
Cardew
So, despite some people saying you didnt test this scientifically well enough ! is it still right that electricity is the cheapest way to heat a small amount of water? Even if you didnt test to this or that standard, you cant have been that far out on the results??

thanks
Originally posted by hypnosisderby
The problem in any comparison is that the longer it takes to heat the water - the more heat is lost.

A 3kW kettle heats quickly, and is well insulated at the base.

Gas takes longer and more heat is lost, but gas is about one third of the price of electricity.

I suspect that there are only fractions of a penny difference for most people.
• bikerchris
• 6th Jan 13, 6:35 PM
• 153 Posts
• 106 Thanks
bikerchris
I'm agreeing with anyone that sounds cleverer than me (easily done!).

Incidentally, I think I may have incorrectly measured the gas usage, kind of assumed how the units work on the imperial type gas meter. It records like this:

1234.56 - then what I thought was a dial indicating 1/10ths of a 1/100's amount. Originally I think I recorded 0.003. But I've seen the dial make a complete revolution and this doesn't seem to change 1234.56 to 1234.57. It seems to take 10 complete revolutions to change 1234.56 to 1234.57 (hope I'm making sense!).

So in theory (with my poor maths knowledge), I actually used 0.0003 perhaps?
If someone is worth thanking - click on the 'Thanks' button on their response. It's just a nice thing to do :-)

Started debt at 17, stopped by 25 :-D ...I'm in debt again because of property :-/
• HappyMJ
• By HappyMJ 6th Jan 13, 6:41 PM
• 20,595 Posts
• 17,201 Thanks
HappyMJ
I'm agreeing with anyone that sounds cleverer than me (easily done!).

Incidentally, I think I may have incorrectly measured the gas usage, kind of assumed how the units work on the imperial type gas meter. It records like this:

1234.56 - then what I thought was a dial indicating 1/10ths of a 1/100's amount. Originally I think I recorded 0.003. But I've seen the dial make a complete revolution and this doesn't seem to change 1234.56 to 1234.57. It seems to take 10 complete revolutions to change 1234.56 to 1234.57 (hope I'm making sense!).

So in theory (with my poor maths knowledge), I actually used 0.0003 perhaps?
Originally posted by bikerchris
So...0.8 pence compared to 0.76 pence. A difference of 0.04 pence. 8 times a day 365 days a year makes a difference of about £1. Not much is it.

Regular savers earn 6% interest (HSBC, First Direct, M&S) Loans cost 2.9% per year (Nationwide) = FREE money.
• psic88
Hi, MSE Geeks
Recently I have had to resort to a combination of kettle [1kw], and saucepan [large not huge] on a gas cooker, to heat water for washing up, because my combi boiler has broken down.
To fill the washing-up bowl I need several kettles and saucepans, each of which is about 1.5l to fill the 9l bowl.
I fell to wondering, as I refilled and heated the various vessels, which is cheaper?
I know gas is cheaper, per kW, but also incurs greater losses.
Is there any significant difference in the overall cost? You can assume that, after the 1st load, the energy used in heating the vessel is not lost.