Cost of boiling a liter of water for tea, coffee etc

Jaffa_cake

Hi all.

I am trying to work out how much it costs me to heat a liter of cold water, to use for tea or coffee.

My electric cost per unit is 14.19 pence per kW
My gas cost is 3.07 pence per kW.

I would use a 2kW plastic electric jug kettle, with the immersed element directly in the water at the bottom, or a metal whistle kettle, that sits on one of the gas hob thingies.

The things that complicate, this seemingly simple calculation is.
1) thermal transfer from heat source to water
2) As the water is heating up, the loss of water temperature due to conduction to the cooler surrounding air.

ie, the metal kettle on the gas hob, would loose more water temperature, than say the plastic, electric kettle, as plastic is a better heat retainer than metal.

Get my jist ?

So, it seems on the surface of things, it is cheaper to use gas to get my water to boiling point, as the electric units are almost 5 times the cost of the gas units.

Any one care to have a go at some calculations ?

coffeehound

I doubt that heat loss by conduction and radiation to surrounding air will be significant in the time it takes to boil a kettle. The electricity use is easy to calculate, but for the gas I think you'd want to measure the amount of gas used rather than apply a nominal kW rating.

Autumnella

I have no idea which would be cheaper... but you need to shop about for a cheaper tariff, then you won't need to worry about the cost of making a cup of tea. Those prices are expensive, with the savings you could make you could makehundreds of cups of tea!

CashStrapped

This question has been posited many times on the forum over the years. Search google and you will find the requisite calcualtions.

The summary, from memory, was that the kettle is more efficient at point of use specifically in thermal efficiency and therefore cost (even though gas is cheaper).

There were however many variables. Type of gas hob, type of gas hob kettle/pan so on and so forth.

However if you take into account the efficiency over the national grid, then gas is more efficient from a carbon foot print point of view.

Basically, it is a can of worms because there are lots of "efficiencies" to be considered.

But at point of use, the electric kettle seemed to win in terms of cost.

I think that was the gist....if I remember.

However, as Autumnella points out, your rates to appear to be very poor.

Get comparing and switiching!!

Pincher

The most cost efficient method is to heat only the water you need with a microwave. No need to heat up the kettle at all.

With gas central heating, the old non-condensing boiler was lucky to get 70% of the heat into the water. With a Band A condensing boiler, you might get 92%. When you heat a kettle by gas, you are lucky if 50% of the heat gets to the water. With an electric kettle, the heat gets to the water first, so you are getting almost 100%.

It all changes when you consider the cost of time wasted waiting for the kettle or microwave to boil.

I have an InSinkerator HC-1100C, which took quite a lot of effort to plumb in, but it's so worth it. Very simply, it keeps a small tank of hot water ready to go 24/7. It's insulated, so the heat loss is not great. Imagine how much time it has saved me and other members of the family, over eight years.

The current model appears to be HC-3300C, which is on offer from Costco at £299.99 + VAT = £359.98

r2015

A few years ago I used a plug in energy monitor and in the course of a day my kettle used 1 kWh of electricity (actually 997 watts) to boil water for 8 mugs of coffee and 2 teapots of tea.


365 kWh a year costing at that time 10p per kWh gives £3.65.


It would take about 100 years to recover the cost of a InSinkerator HC-1100C, not including the electricity costs or installion costs.

Pincher

Pincher wrote: »

It all changes when you consider the cost of time wasted waiting for the kettle or microwave to boil.

r2015 wrote: »

It would take about 100 years to recover the cost of a InSinkerator HC-1100C, not including the electricity costs or installion costs.

How much do you consider your time to be worth?

If you get paid £6 an hour, that's 10p per minute.
8 coffees and 2 teas. Let us assume you wait one minute each for ten drinks a day, that is £1 a day you wasted.

£359.99 is so close to £365, it's uncanny

Biggles

Pincher wrote: »

How much do you consider your time to be worth?

If you get paid £6 an hour, that's 10p per minute.
8 coffees and 2 teas. Let us assume you wait one minute each for ten drinks a day, that is £1 a day you wasted.

I don't know if many people stand, doing nothing, just staring at their kettle while it heats up (though it's only a few seconds to heat enough for a mug, say 300ml, to the required 80° or 90°) . In any event, the main time factor, when making a decent coffee or tea, is the three or four minutes it takes to brew.

For that, there is just one word - multitasking. No time is wasted.

missbiggles1

Pincher wrote: »

How much do you consider your time to be worth?

If you get paid £6 an hour, that's 10p per minute.
8 coffees and 2 teas. Let us assume you wait one minute each for ten drinks a day, that is £1 a day you wasted.

£359.99 is so close to £365, it's uncanny

Unless I'm at work, my time's worth nothing but, if you tell me who pays for yours, I might sign up.:D

ETA
If I drank 10 hot drinks a day, I'd spend far more time in the loo than I would waiting for the kettle to boil!

Cardew

As said above, this question has been posed many times on MSE and always reaches the same inconclusive result.

DigForVictory

Cheat...
https://forums.moneysavingexpert.com/discussion/5471068

No more minutes waiting - seconds.
Then with brew in hand, read this? http://www.moneysavingexpert.com/utilities/you-switch-gas-electricity