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Name: John
Status: Other
Grade: Other
Location: TX
Country: United States
Date: June 2008

Which is the more efficient (energy-wise) way to boil a cup of water: on a natural gas stove top, or in a microwave oven?

Hi John,

There are far too many uncertainties here, to you an accurate answer. At first glance, the microwave sounds like it should be the most efficient, since all the microwave energy ought to be directed into the water. But it is nowhere near as simple as that. In a microwave oven there are two main areas of inefficiency. First, the microwave oven's magnetron tube is itself not very efficient and generates a lot of wasted heat (that is why the oven has a large cooling fan). Second, with something as small as a cup of water, a lot of microwave energy is not captured by the water, but ends up being reflected back to the source (the magnetron) and dissipated as additional heat (another reason for that big fan). This is all energy that does not go to heating the water.

In the case of heating the cup of water on a natural gas stove, much of the heat energy is also wasted, especially with such a small amount of water. But in both cases, without knowing far more specific details, such as the shape of the containers, the efficiency of the specific microwave oven in use (they vary widely!), details of the stove's gas burner, etc, I cannot answer your question accurately. My guess, however, is that the microwave will usually win.


Bob Wilson

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