A microwave oven uses less energy than a conventional oven. Even though this statement is broadly true, a microwave oven isn’t always the most efficient way to cook.
So what appliance should you use to heat up or cook your dinner: A gas stovetop? An electric-resistance stovetop? An induction stovetop? A gas oven? An electric oven? A countertop toaster oven? A crockpot? Or a microwave oven?
If all you care about is energy efficiency, it’s possible to come up with an answer to this question — but the answer will depend on the quantity and the type of food you are cooking.
If you care about the taste of your food, on the other hand, energy efficiency probably doesn’t matter. For example, if you are cooking a traditional paella, the answer is, “An open fire fueled by prunings from a vineyard” — and energy efficiency be damned.
Comparing a microwave oven to other cooking methods
A microwave oven uses quite a bit of power — between 950 and 1,720 watts — but it usually isn’t operated for long. According to a 2001 Home Energy article, “the typical residential microwave oven consumes about 110 kWh of electricity per year.” If you are paying 15¢/kWh for electricity, your microwave oven is costing you only about $16 a year to operate.
According to The Consumer Guide to Home Energy Savings, a publication of the American Council for an Energy-Efficient Economy, cooking a casserole costs 16¢ if you use a conventional electric oven; 8¢ if you use a toaster oven; 7¢ if you use a gas oven; 6¢ if you use an electric crockpot; and 3¢ if you use a microwave oven. (These calculations are based on the assumption that natural gas costs 60¢/therm, and electricity costs 8¢/kWh. To bring these estimates roughly in line with current energy prices, the estimated costs should be increased by 40% to 100%.)
However, there are many factors that affect these types of comparisons.
Microwave ovens use less energy than conventional ovens — unless you are cooking a large quantity of food. Baking four potatoes in a conventional oven takes 2.5 as much energy as baking four potatoes in a microwave oven. But if you are cooking an entire meal for a big family — for example, a meal described by Swedish researchers as “a pot roast plus vegetables” — the conventional oven will use less energy. The food will probably taste better, too.
What if you just want to heat up a cup of water for tea? The most efficient way to heat water for a mug of tea is to put the water in a teakettle and to heat it on an induction cooktop or an electric-resistance stovetop. According to measurements made by Jennifer Mitchell-Jackson at Lawrence Berkeley National Laboratory, an electric resistance burner uses 25% less electricity than heating the water in a microwave oven. Be careful, however: if you overfill the teakettle, you may end up boiling more water than you need, negating the energy savings. While a gas stove uses more energy than a microwave oven for this task, the gas stove method will probably cost even less than the electric stove method. (Mitchell-Jackson didn’t test any induction cooktops, which are even more energy-efficient than electric-resistance burners.)
A microwave oven doesn’t heat up your kitchen as much as a conventional oven, reducing the load on your air conditioner. Of course, this factor only matters during the summer.
If you can fit the food you are cooking into a countertop toaster oven, cooking it there will use less energy than a conventional electric oven.
Remember, natural gas usually costs less per BTU than electricity. The Home Energy article noted, “One hour in a gas oven costs approximately the same as 30 minutes in a microwave.”
Standby power use
The federal government currently has no energy efficiency standards for microwave ovens, either in standby mode or in operating mode.
According to a study by researchers at the Lawerence Berkeley National Laboratory, the average standby power use for microwave ovens is 3.08 watts (27 kWh per year). Measured values range from 1.4 watt to 4.9 watts.
If you don’t remember to close the door of your microwave oven after using it, the average standby power usage jumps up to 26 watts. So close the oven door!
While the standby energy use of a microwave oven isn’t huge — at 15¢/kWh, the average cost of this standby power is only about $4 per year — it’s still a fairly significant amount of power. If you only use your microwave oven for 20 minutes a week, then you are paying more for standby power than you are for heating your food.
New standards will address standby power use
The U.S. Department of Energy has recently enacted regulations that will eventually regulate the standby power consumption of microwave ovens.
The new regulation will require countertop microwave ovens to use no more than 1.0 watt in standby mode. Built-in microwave ovens will be required to use no more than 2.2 watts in standby mode. The new regulation will take effect in 2016.
Don’t worry about it
Energy used for cooking amounts to between 3% and 4% of residential energy use in the U.S. This category of energy use is dwarfed by other categories like space heating, cooling, and domestic hot water.
There is little difference in efficiency between one brand of microwave oven and another. The 2001 Home Energy article reported, “To find out just how efficient microwave ovens are, we tested ten different models using a procedure that closely resembled the International Electrotechnical Commission’s standard method for measuring microwave oven performance. … We found that the microwaves’ average efficiencies (the ratio of the electricity that went to heat food or water in the microwave divided by the total electricity used) ranged from 49% to 57%. These results were comparable to those from a 1994 study by Lawrence Berkeley National Laboratory (LBNL) which measured microwave efficiencies at 48%–60%. … Don’t worry about which brand to purchase, since the range of microwave efficiencies tends to be small.”
Here are the important points to remember about microwave oven use:
- A microwave oven almost always uses less energy than a conventional oven.
- You won’t discover much of a difference in energy efficiency when comparing different models of microwave ovens.
- The amount of energy used by a microwave oven is relatively small, so any tricks you can devise to reduce the amount of energy used by your microwave won’t save much energy.
- Food cooked by sautéing, frying, oven-roasting, broiling, or grilling over an open fire usually tastes better than food cooked in a microwave oven.
- If you want to reduce the amount of energy you use for cooking, consider buying an induction cooktop.
- If you live in an off-grid house, your PV array may be producing “use it or lose it” amounts of energy during the summer. If that’s the case, heating up your lunch with a microwave oven is a good way to save propane.
Martin Holladay’s previous blog: “Get Ready for Smart Appliances.”