Which is more energy efficient: heating a given volume of water all at once, or in two batches?
I have an electric kettle, and a large urn of room temperature filtered water, which I use for tea. If I'm making tea for two people who aren't going to be drinking it at the same time, is it more energy efficient to boil the water separately, all at once, or no difference?
@Fishercat I'm pretty sure the key to efficient hot water is small surface area where things cool down. Chances are heating it all at once in one big batch is going to give you the optimum here. If you are thinking about re-heating, the number of varables grows way too large for me to make an educated guess.
If you want to make sure your'e actually doing things right, you could always do the experimental sciency route and record a statistically relevant batch of data, analyze it, consider what might've scewed the data and draw your conclusion from there.
Ah. I'm enough of a purist that I only boil as much water for tea as I'm going to use immediately. If I boil or heat the same water more than once, the tea isn't as nice.
I could go the sciencey route, but it was just an idle thought as I was making tea. I'm more interested in the answer, which I was sure other people would already have, than repeating the experiment(s) myself.
@Fishercat
I think it is more efficient to boil it separately, depending on how long there is between the two usages and if you want to make sure the second cup is as warm as the first.
The difference is the heat loss from the water left in the kettle after the first cup. When the water is left warm in the kettle the temperature will slowly decline. And if you want the second cup to be just as warm, you need to heat it again.
I can think of cases where it would be more efficient to boil it all at once, but I don't think that would ever apply to an electric kettle.
(if you were using an iron pot over a stove, boiling the water would require extra energy to heat up the pot as well, which you would need to do again for the next cup)
​@Fishercat Heating 400ml of water to a boil will take exactly twice the energy of heating 200ml to a boil. In the latter case you'll need to heat the kettle itself twice, but that ought to be insigficant; or rather, choose one that's light weight and heats easily if you care about efficiency, and then it will be insigficant.
The main thing is to not heat more water than you need, which is where the bulk of the energy is spent.
@tfb Thank you!
I do have a lightweight kettle, where the heating element is in direct contact with the water. IIUC, that design & method of heating water is far more efficient than any where the vessel has to heat before the water does.
I never do heat more water than I need, both to avoid wasting that energy, and because reheating/reboiling water reduces the flavor of whatever you make with it.
Fishercat
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