Dear Umbra,

My roommates seem to be constantly boiling water for tea. We’ve got a gas stove, a microwave, and an electric teakettle. However, we don’t know which option is most efficient. Any ideas?

Kate R.
Syracuse, N.Y.

Dearest Kate,

Idears-R-Me, and microwaved tea is nasty. Nas-tea, I suppose I must say, if I wish my membership in the Cheap Joke Association to be renewed.

To nuke or not to nuke?

Photo: iStockphoto

To recast your question in another way: which of these appliances spends the most energy heating the water and the least energy heating itself, the air, or any other involved items? A review of the literature (various governmental energy-efficiency advisories, like this one from Canada) indicates that the electric kettle is No. 1 in efficiency. Let’s use logic to arrive at the same conclusion.

First examine the gas range as it heats a vessel filled with water. Note the open flame, which may or may not fit underneath the vessel. The flame is merrily heating the vessel, which must be well heated before the water can begin to warm. The flame is also — it cannot avoid — heating the nearby air. How much of the gas heat is lost around the edges of the vessel will of course depend on the size of the vessel, the size of the flame, and the operator of the stove.

You may be interested to learn that microwave oven digital displays are responsible for the lion’s share of their power draw — 80 percent, by one reckoning. (This means unplugging microwaves when they’re not in use is a good way to increase their efficiency and decrease your overall energy use. Ditto for other home appliances and electronics.) In terms of efficiency, the microwaves inside the oven work their magic and heat only the targeted object, not the enclosed air, nor is any of the microwaves’ embodied energy lost as a byproduct of combustion. There is no combustion. The waves (micro, as established) hit the water and the cup itself, causing their molecules to bounce about, rub against one another, and become hottish. Microwaves are very efficient at heating food, but in my opinion, microwaved water doesn’t hold heat long enough to make decent tea. And overheating water in a microwave in an effort to get it sufficiently hot is dangerous. If your roommates prefer weak tea in tepid water, however, who am I to interfere? Bleagh.

The electric kettle has a heating element in direct contact with the water. If the kettle itself is an efficient model, little heat will be lost to the vessel or the surrounding air. When the water has been heated (hopefully boiled), the same efficient kettle should automatically shut off. Alright, I said logic, but logic does not tell us why a microwave is less efficient than a kettle at heating water, unless my snooty opinion about poor water heating in a microwave is actually germane. I’ve been looking for widely accepted efficiency percentiles on these three items to no avail. An efficiency percentile would tell us how much of the energy spent actually went to heating the water — you can find this type of number for a home water heater, for example.

All I can tell you, in conclusion, is that the government energy-efficiency advisories prefer the kettle over other means. Let’s trust they’ve done the analysis, and are not all just copying each other and creating one giant chain of misinformation. Fortunately this is a very small matter compared to issues such as personal vehicle emissions, and we can trust that going with the kettle is probably not so bad.

Firmly,
Umbra