Stove Versus Microwave Efficiency
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?
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.
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Update: June 2012