Boiling water on gas stove vs electric kettle

Which is more energy efficient - boiling water using an electric kettle, a kettle on a gas hob or a microwave oven?

• IT TAKES the same amount of energy to heat one litre of water no matter which method of heating used. The only difference in the methods is the amount of time each takes. However, the eletric kettle may prove to be a little more efficient on the basis that when the water has fully boiled it switches itself off, the other methods require a watchful eye to stop the power when the water has boiled.

  Ben Hendy, Bournemouth ()

• UNFORTUNATELY, not all the energy applied goes into the water. A kettle heats itself as well as the water in it, and some of that heat is conducted/radiated away as the kettle is brought to the boil. Microwaves are designed specifically for heating water (in food) so the microwave energy heats nothing but water. The imponderable is how efficient the microwave machine is at converting electricity into microwave energy. No doubt manufacturers make different claims about this.

  Arthur Wardell, Halifax, ()

• THE KETTLE on a gas hob, because gas is a primary energy source. Electricity is generated by burning gas or coal in a power station at somewhere between 30% and 50% efficiency. Heating by microwaves, generated from electricity, is even more inefficient.

  John Ackers, Islington Friends of the Earth, London N5.

• HAVING conducted out some tests in the kitchen using the three implements the efficiency rating is: 1st kettle, 2nd microwave, 3rd gas, based on efficiency of the energy entering your house. However the overall efficiency would have gas in first place due to the losses of 50%  70 % incurred in the generation of electricity from its base fuel.

  Matthew Guite, Staines, Middx ()

• TO BOIL a given quantity of water from room temperature will require the same amount of energy whatever the source. Inefficiency in the form of energy losses will arise from heating the container, surrounding items, ie. gas hob supports, kitchen work top and the surrounding air. Insofar as the microwave oven heats only the water and indirectly the container and a limited amount of air while providing a modeslty insulated environment, this will incur less heat loss than the other methods and so should be the more efficient. However, a more thorough analysis should consider the efficiency of the energy supply process and on this basis possibly the gas hob may be more energy efficient given that power stations are only about 30% efficent in converting primary fuels to electricity, whereas energy losses in supplying natural gas will be somewhat less and incurred in the transmission of the gas to consumers.

  David Bridgewater, Pershore, Worcs. ()

• 'One accurate measurement is worth a thousand expert opinions’ Grace Murray Hopper Using a ‘plug in’ power meter I have measured the efficiency of boiling 1 litre of water in a two types of kettle (stainless steel and plastic) and a microwave. I have also measured the gas used to boil a pan of water on my gas hob. The sums are the sort you learn for GCSE science. Kettles; 65% Microwave: 30% Gas kettle: 25% You have to remember that gas is about a third the cost of electricity per kWh (or Unit or Joule) and also has a third of the CO2 emissions. In this test gas has a small advantage, which may be improved with a lighter more efficient kettle. The electric kettle has the advantage that it turns itself off automatically. While the microwave was inefficient bringing water to the boil, it was more efficient when only warming it to 50 degrees C at 45%.

  Andy Brown, Cambridge UK

• Tested the system based on 600mls of water using a 1.2kw microwave rated at 800w output . It took 8 mins 40 second to bring to the boil. The kettle took 4 mins 16 second adjusted for the same kw output. Microwave is only 60% efficent in using energy relative to what energy goes in and the microwaves that come out. Typically is is operating at about half the efficiency in my kitchen relative to boiling water in a kettle. The kettle wins out. However if I was comparing with an oven for conventional cooking the small size may offer some advantages over heating the large bulk of a conventional oven. Microwaves can heat food effectively from the inside and so dont have to wait for their surroundings to heat up. Therefore dont boil water with microwave but do consider them if you like rubbery poorly browned food.

  tony price, mouldsworth england

• Informative discussion. The amount of gas required varies considerably: In particular the kettle design. Our trendy design (wife's choice) kettle loses flame heat around the sides to heat the room as well as the water. Its dark green colour re-radiates and wastes a lot of heat. The flame height has a lot of effect. Too low and the heat in-heat wasted will balance and go nowhere. Too high and the flame just misses most of the metal body. An old kettle of my mother's had a skirt around the bottom that held more of the flame in contact with the base and prevented it skirting up the side. It appeared to boil quite quickly. Of course, only boil what you need.

  Alan Strickland, Adelaide, Australia

• During Winter in a caravan, gas hob kettle wins hands down, because the omitted heat warms up the surrounding area in time for your first cup of tea!

  Andrew Vaughan, Tickhill, United Kingdom

• Following from a comment above about the efficiency of the microwave oven, if it is 60% efficient where is all the wasted energy going? The electrics don't get very warm, nor does the case, there is little light or noise emitted so is the first law of thermodynamics wrong?

  Ian, Nuneaton Warwickshire

• If you take into account the efficiency of getting the power to you from source, which you should, John Ackers has it exactly right - as gas is a primary energy source it is definitely the most efficient.

  Klina Jordan, Oxford UK

• Greenest and cheapest (for Adelaide) method is gas cooktop as it uses the primary energy, even though the heating efficiency is low compared to others. Next option would be microwave as it heats up only water. Next option would be an electric kettle as it has low heat loss. Induction cooktop is also good option. Never use electric cooktop.

  Ramadas, Adelaide Australia

• Again, heating of 1 litre of water from 20oC 100oC need 330kJ (0.091kWh) of heat. All these method provide the this amount of heat to water. If you look the kettle which will have about 90% effciency, require 0.183kWh of electricty. Mircowave has about 66% effciency requires 0.139 kWhr of electricity. The natural gas cook to has about 50% efficency, so they require 660kJ(0.183kWh). But cost wise the order is different. For Adelaide tarrif rates, gas is coming as chepaest with 1 cent where as 3.4 and 4.7 cents for kettle and microwave. If you look at the CO2 emission, it can be estimated as 33, 88 and 112 grams of CO2 for gas and kettle and microwave. In total, Gas is the winner, runner-up is kettle. Stop, another challenger, Inducction cookop... may come 2nd... not the winner!!

  Ramadas, Adelaide Australia

• After a quick test just between the electric kettle and the microwave. I found there to be no insignificant difference between them. My kettle input is 3000W My microwave input is 1400W So using 100ml at the same starting temperatures. I put the microwave water in a small plastic sealed container. I also take the glass dish out of the microwave. I started the microwave on high for 60 secs, and then the kettle at 30 secs. At the end the water was approx the same temperature. I am not able to test the gas hob as I have no way of measuring the amount of gas used. How would anyone do that?

  Andy Walsh , Preston United Kingdom

• In response to Ian from Nuneaton. The energy losses in a microwave are from heat generated from the magnetron, the AC power transformer, the light, the motor drive for the turntable, the control circuitry and the fan to dissipate aforementioned heat. This accounts for 35 to 40% energy losses.

  John Shaw, Buxted England

• In my test at home, the microwave required 1650W input for 120 seconds, but the electric kettle required 2000W for 145 seconds to produce boiling water for a cup of tea. In my case the electric kettle is less efficient for making a single cup (which is my primary use). This is because the kettle requires a minimum fill of 500ml of water and I only need around 350ml.

  Richard Hertz, Upton USA

• This experiment was done on the NSW Central Coast 20th July 2013. Any costing refers to NSW values. To boil 1 litre of water in a Circulon kettle on an Ariston gas cooktop took 5mins 5secs and used 0.019cu.metres gas. 1cu.metre=39.3547MJ and 1MJ=$0.02967. COST 0.019x39.3547x0.02967=2.22cents. To boil 1 litre of water in a Russell Hobbs electric jug took 2mins 45secs and used 0.112kWh electric. 1kWh=53.592cents Peak 1kWh=21.842cents Shoulder 1kWh=13.42cents Off Peak Peak 7am-9am, 5pm-9pm Shoulder 9am-5pm, 9pm-10pm Off Peak 10pm-7am COST 0.112x53.592=6cents Peak 0.112x21.842=2.45cents Shoulder 0.112x13.42=1.503cents Off Peak Therefore in NSW it is cheaper to boil water by gas unless you feel like getting up in the middle of the night. Although Shoulder period electricity is only marginally more expensive than gas a working couple would be mainly boiling their water during the Peak period.

  Barry Shearman, Woongarrah Australia

• Kettle on top of wood burner if burner on anyway. Another tip with electrics, don't keep re boiling the kettle if it goes off the boil. You won't have to let your tea cool, you won't burn the tea/coffee, it'll still brew and taste lush and be at perfect temp. Peace. X

  Neal, Hereford, England

• My priority for boiling a kettle is how little noise it makes, not how fast it boils or how efficient it is. Gas wins hands down. Most electrical appliances are built to achieve a low selling price, which in most cases means a high noise level. A gas kettle is so quiet, why is everyone in so much of a hurry, chill out, relax and have a cup of tea!

  John Smith, Rotherham, Great Britain

• Based on the above answers and examples, to boil 1 litre of water from 20C to 100C, requiring 0.183 kWh of either electricity or gas, at todays energy prices GAS is 68% cheaper than electricity.

  Randy Robinson, Leominster, UK