[Closed] Heating Water, which uses more energy or is quicker?

Dunno, but off the top of my head I'd say that the "adding more" route would involve more generation of steam and hence be more wasteful?

Ooh an angle I hadn't considered! 🙂

You put heat into the pan, it boils.

A warm or hot pan loses heat to the environment.

The hotter it is, the more heat is lost to the environment. So the more time it spends at a low temperature the better. Plus, if it's actually boiling then the evaporation into steam is removing a lot more heat from the pan in addition to that caused by it simply being hot.

Pure Physical Chemistry Answer...
It takes an amount of energy to increase the temp of a substance by an amount no matter how you do it. The rate of transfer may differ.

Real world way too complex see myth busters

The surface area to volume ratio is higher for smaller cylinders so a less full pan may waste relatively more during heating.

But on the other hand the absolute surface area will be smaller until near the end of the heating process so it may actually lose less heat overall.

So I dunno.

A warm or hot pan loses heat to the environment.

Thinking out loud ...

The pan will lose heat proportional to the temperature difference between the inside and the outside, and also proportional to the surface area.

If you imagine some sort of magic pan that is always just big enough to hold what you pour into it, then for the "adding more water" case, the temp diff will be bigger, but the surface area will be smaller (until the very last moment). I suppose a competent person could work out which effect was bigger 🙂

With an open pan, most of the heat loss is due to evaporation and convection from the top surface, and unless you have a very odd shaped pan then the open surface area is constant no matter how much water you have in the pan. Hence the larger temperature differential when adding cold water later results in more heat loss. The surface area available for heat loss directly from the pan will actually be greater with less water so again more heat loss with the adding water later method.

With a closed pan, the external surface area for heat loss is constant no matter how much water you have in the pan, hence the larger temperature differential when adding cold water later results in more heat loss.

For all cases I'm assuming the temperature of the pan itself is constant across the pan, but that's not a bad assumption for a metal pan which conducts heat well.

In summary the quickest way to boil the water and the most efficient is to put all the water in the pan at the start.

And this is why I will always be on this forum even if I stopped cycling.. love this place 🙂 Thanks all.

Is the kettle on a treadmill?

OK so alternative situation, you have 1 litre of boiling water and 1 litre of room temperature water, when combined will the liquid reach boiling point faster if you drip the cooler water in steadily or if you added it at once, or would it make any difference at all.

In theory same water same energy to boil, I'm wondering if there is a efficiency gain from never letting the water cool to much

Put a lid on it!

[quote=bluemonkey ]OK so alternative situation, you have 1 litre of boiling water and 1 litre of room temperature water, when combined will the liquid reach boiling point faster if you drip the cooler water in steadily or if you added it at once, or would it make any difference at all.
In theory same water same energy to boil, I'm wondering if there is a efficiency gain from never letting the water cool to much

You're heating the water after combining it?

For the same reasons I explained above, the best thing to do is mix it all at the start.

The theory of it taking the same amount of energy to boil is ignoring the heat losses, which is where the important differences are - no there is no efficiency gain from not letting the water cool, on the contrary there is an efficiency gain from cooling the water as the temperature differential to the environment is lowered hence reducing losses.

Best thing to do is to put the water you need in the kettle and boil it.

Hot water out the tap then in the kettle then in the pan. Work that ****er out statto.

wrightyson - Member
Hot water out the tap then in the kettle then in the pan. Work that **** out statto.

We have to allow the running of cold water cost prior to it being heated by the combi as well. 😆

We have to allow the running of cold water cost prior to it being heated by the combi as well. 😆

When was the boiler last serviced?
Does it run on mains gas?

Serious question now. Dirty sex pool content.
Would it be cheaper to fill the hot tub with the hot tap direct from the combi or let the tub do it? This time of year water is around 13 degrees out the tap and it heats roughly 1.5/2 degrees an hour up to 38 degrees. Fills in around 90 mins.

I boil cold water in the kettle then add it to an empty pan,that I start heating as the kettle boils.I don't have much rationale for this,except 1) the kettle is quicker, and 2) the kettle element is completely immersed in the water,whereas the flame loses a lot of heat to the room.It works for me 😀

a kwh of gas is much cheaper than a kwh of lecky, so cheaper to fill the sex pond off the hot tap?

This raises questions in my mind about the kettle method.

Just have a glass of milk.

Instead of the mucky sex puddle, not the brew, obviously.

When I fitted a new washing machine, the old one had both hot and cold water inputs. The new one is "cold fill only". Apparently, it's more efficient for the washing machine to heat the water rather than rely on the supply.

Totally irrelevant to the OP's question - just thought I'd share this snippet of priceless information.

Hot water out the tap then in the kettle then in the pan

if the boiler like ours is miles away from the tap, then for half a kettle of water I am heating about 10m of pipework and water which is then allowed to cool in the pipes. so cold in the kettle and boil, add to pre-warmed pan and put lid on.