Microwaves vs. Ovens: What’s the Greenest Way to Heat Your Food?

for heating water, microwave method should be the most efficient way b/c at your end-game, when the water is boiling for example, on a stove you have alot of residual heat from the hot stovetop and pot etc. In a MW, the only thing that gets heated is the water!

and of course the heated air coming off the heated water, but thats true in both cases.

also, that heated water from cooking pasta- dont throw that down the drain in the winter! just let it sit out and enjoy its residual heat

Microwaving food in a plastic bowl...you ought to worry more about your food consumption than your energy consumption.

"Glass and ceramic cookware conducts and retains heat better than metal."

Um, no. Something can conduct better or retain better, but those two things are diametrically opposed. Glass and ceramics are insulators. they retain heat, but they do not conduct it better. That doesn't mean they aren't good for cooking, but there is a reason you don't use a glass pan on the stovetop.

Also, it would be nice if you gave a general indication if stoves are more or less efficient than microwaves. It's like you started to, but I have no idea how many BTUs my stove puts out, or the relative greeness of the natural gas stove versus the electric microwave.

"Using a microwave will reduce your energy consumption by about two-thirds compared to using a regular oven. Microwaves also create less heat so require less air conditioning in the summer." - Energy Hawk site

Your title is misleading as there is nothing in the article that directly answers it. But I found the answer at Energy Hawk.

I have to wonder about this one:

"Glass and ceramic cookware conducts and retains heat better than metal. If a recipe calls for a metal baking pan, switching to glass or ceramic allows you to lower the oven temperature by 25 degrees."

If it retains heat better, it also heats up slower. Is this really from the Union of Concerned Scientists? Is there scientific evidence for this claim?

The baking pan choice recommendation is way off base .Only someone who slept through high school physics would recommend a heavy glass pan with low conductivity over a thin black metal pan one with high conductivity. Look at the baking time recommendations on a brownie mix for goodness sakes! Y

Glass does make sense if one is planning a casserole type dish that you want to stay warm on the table. However, from a pure cooking efficiency. the thermal inertia of glass is just going to cause energy overshoot.

They also missed a key recommendation. The entire "pre-heating of the oven" thing is superstitious nonsense. Right up there with laundry detergent that produces suds (suds is a relict cultural expectation from the days of washing clothes with shaved soap bars, where the presence of suds indicated adequate soap)

I've been turning on the oven when I put the food in for my whole life and have been warned time and again by the women in my life that I will "ruin the recipe" And time and again it always turns out fine.

Also, not only is the physical diameter of the pan important, but so is the thickness. Frying eggs with a thick pan is a huge waste of energy - most of the burner output is left in the pan when the eggs are done. Get the same work done with half the energy by using a thin cheap pan - the kind sold in grocery aisles. This is one case where efficiency trumps beauty every time.

Aaron Huertas here with UCS. Just wanted to respond to a few points.

To Steve L - The answer to which appliance is more efficient depends on what brand and what power of each appliance you have - thus the calculations at the end. A small oven, for instance, might be better than a very powerful microwave. We wouldn't want to blanketly recommend something that might not apply to some individuals. So officially, the answer to the title question is: Check out your appliances and find out! For my kitchen, the answer is definitely the microwave.

To Charlie and JL - Ceramic and glass cookware manufacturers recommend reducing temperatures 25 degrees while baking the same amount of time, thus using less energy. I've found the tip in a couple places and will take some time later today to figure out the science behind that recommendation and post it here.

And to JL - The post did include a tip about not pre-heating your oven. And thanks for the tip on cookware thickness!

-Aaron

At first blush the data this gives you on watt-hours with a microwave and a gas stove makes it look like a gas stove is better @ only 0.293 watt-hours, but thats for only 1 BTU. The average kitchen stove burner is 8000 BTU. That means over 2300 watts an hour..

If I'm thinking wrongly about this someone let me know lol.

Slow thermal transfer works both ways. Glass is slower to heat up, but slower to cool down. So the glass continues to cook the food after the oven is turned off. Same for cast iron cookware. Which pan is the most efficient? Like all things discussed on TH, there is more than one answer. It depends on the application, the appliance, the food, the cooking time, etc. Using energy efficient appliances and following the basics outline above is going to make the biggest impact on energy consumption, and the finite savings thereafter would generally be offset by the multiple utensils and appliances required to maximize every cooking endeavor.

Microwaves should NOT be used. PERIOD. Not only does the majority of cookware labeled "microwave safe" leach toxins into your food, microwaving food is believed to physically change the structure of the food and to destroy up to 90% of its nutrient value. The only pertinent question is how to dispose of it in an ecologically sound manner.

Thanks, Aaron.

One consideration is the emissivity of the bottom of the pan--how well it absorbs infrared radiation. Shiny aluminum reflects most of the radiation. Metal with a dark coating absorbs it better. Glass is transparent to some infrared radiation, allowing it to reach the food directly, but absorbs longer wavelengths just like a dark metal pan would. In either case that's an advantage compared to a shiny pan (for energy efficiency).

But the thick glass is slower to heat up than thin metal, so there's a tradeoff, and the net result might be different depending on cooking time and temperature--in some cases the cooking might be shorter with glass than with shiny metal (for a given temperature); in others the shiny metal might be better than glass. We can, however, expect that thin dark metal will lead to the shortest cooking times in most cases.

So either experiments or more detailed modeling would be needed to determine whether glass or metal was faster for a given situation. Linked from my name is one detailed article that shows that cakes cook significantly faster in a metal pan than in a glass pan.

"Glass and Metal Pans for Use with Microwave- and Conventionally Heated Cakes,"
B. A. BAKER, E. A. DAVIS, and J. GORDON
Cereal Chem. 67(5):448-451, 1990.

Soak your beans and grains for reduced cook times and increased nutrition!

Aaron Huertas with UCS again. The anonymous poster who said ceramic and glass cookware continues to heat food after its done in the oven is right on. I just talked to Richard McNich, Technical Project Manager for Glass, at World Kitchen, Inc., who explained that because glass and ceramic are better insulators than metal, you can cook with them at lower temperatures since they'll continue to heat the food after you're done cooking.

That is primarily an example of "retaining" heat. They "conduct" heat better in the sense that they conduct it longer for the purposes of cooking. However, since those terms are precise, this entry should have been more clear.

Thanks everyone who flagged this issue and for all the other great tips.

Our microwave just stopped working. I found one on sale ($57), so I bought it, but I have several questions before I actually open the box and use it.
First, I wonder if it would be worth it to try to fix the broken one. I am going to call around on Monday. Second, there is an Omnisource recycler where I live, and I believe they take these kinds of products to dispose of them properly. Are there any suggestions about repair and disposal?

Next, I wonder whether a MW is more efficient than a stove or oven (why I clicked on this thread). It seems to me it would be because it starts heating the food right away, instead of having to get hot and heat the pan first. I think that is the consensus here, anyhow.

Which leads to my next question. I bought a 1000 watt microwave, as opposed to a 700 or 900 watt, thinking that I could warm food in less time, thereby saving energy. But after reading these posts, I'm not sure about that. Are there any more comments about MW wattage?

And of course,now I'm worried about the safety of eating microwaved food! We actually don't use it too often. I've been cooking oatmeal on the stove, which takes barely any more time, and reheating pizza in a small skillet on the stove top, in order to not heat the whole oven. I drink a lot of tea, so lately I've been warming the water in the smallest little pan I can. I see here I should use a lid to be more efficient.

Anything anybody suggests to help me out would be appreciated.

@Michael deLisle - Not to throw cold water on your rant against microwaves, but do you have any sources/stats/etc. to back up your assertions? It really does appear that you pulled that 90% number out of your backside.

I think we would all like to know the facts, if you have any, about microwave ovens. Please enlighten us.