Crockpot vs. Gas oven

firebus's picture

Welcome back to the n of 1 institute.

In this episode we'll be comparing crock pot cooking with gas oven cooking. Specifically we'll be comparing my electric crock pot with my gas oven - so it's really an n of ME analysis! n of ME is even less useful than n of 1. Cool! We're going to aim at comparing carbon footprint, but will also touch on a straight comparison of "energy", and a price comparison.

There are a number of internet resources comparing crockpot cooking to electric stovetop cooking. There are fewer resources comparing crockpots to gas ranges or electric overs. There are almost no resources comparing crockpots to gas ovens. Here's the best one I found. Most people use crockpots to replace stovetop cooking, specifically for long-simmered dishes. However, I use the oven for long-simmered dishes that don't need to be reduced - including cooking beans - because the oven provides a more even heat at a lower temperature (so, less chance of getting tough beans from high heat). Obviously a crockpot is a great replacement for a braise.

There's some nuance in comparing electric and gas cookers. To start with, 1 BTU = 0.293 Wh. However, electricity generation in a power plant is inefficient (33% efficient according to the link above) so to compare apples to apples, we have multiply electricity use by 3 when comparing - unless we know that there's renewable energy in the mix. We're going assume a worst case scenario to start with, and then figure out if there's a renewable mix that would change the results. If the crockpot is better in the worst case scenario, I'm too lazy to go into the details.

Additionally, it's difficult to figure out how many BTU your oven is using. Ovens are rated at max BTU output, but when you are baking on a low temperature, the heat isn't on the whole time, and it might be running at a lower level when it's on. Of course, you'll use more fuel to bake when it's cold than you will in the middle of a heat wave (the same is true for the crockpot, although maybe to a lesser extent, so we'll ignore it). Again, we'll take the worst case scenario, and then propose some more reasonable options.

My crockpot is rated at 270 watts. That's really huge, and it's a really huge pot. I should get a smaller one. I've noticed that it takes about twice as long to cook something in the pot on high than it does to cook something in the oven at 250 - so that's another adjustment we have to make.

My oven is rated at 30,000 BTU/hour. Also rather huge. There's an electric ignition element (no pilot light). Max wattage for the oven is 100 W. The first reference above suggests that the electric ignition is always on when the oven is on, so we'll add 100 W and we'll multiply that by 3 as well to compare carbon footprint.

So, in the impossible worst case scenario, we get:

  • Crockpot: 270 W * 2 hour = 540 Wh. 540Wh * 3 (inefficiency coefficient) = 1,620 Wh adjusted for carbon footprint.
  • Oven = 30,000 BTU * 1 hour (remember that the oven is faster) * 0.293 Wh/BTU + 100 Wh = 8,890 Wh. 8890 Wh + 200 Wh = 9090 Wh adjusted for carbon footprint.

Remember that this assumes that the oven is running full blast the whole time, which is not the case for 250 degrees. The next time I bake, I'll take some timings, but until then, let's try to figure out a reasonable number.

  1. The first link above claims, without citation, that a gas oven burns 9,000BTU on "medium", without noting what max power is, and what temperature medium corresponds to. Let's consider this a maximum reasonable value.
  2. This reference compares "gas marks" (which are used in Britain?) with temperatures! Awesome. Gas marks range from 0.25 to 10. Let's pretend that gas marks accurately represent the proportion of full power being used. 250 degrees correspond to gas mark 0.5. If 30,000 BTU/hour is full power (or 10), then 0.5 is 1,500 BTU/hour. Let's consider this a minimum reasonable value.
  • Oven (maximum reasonable value) = 9000 BTU * 1 hour * 0.293 Wh/BTU + 100 Wh = 2,737 Wh + 200 Wh = 2,937 Wh adjusted for carbon footprint.
  • Oven (midpoint) = 5250 BTU * 1 hour * 0.293 Wh/BTU + 100 Wh = 1638.25 + 200 Wh = 1,838.25 Wh adjusted for carbon footprint.
  • Oven (minimum reasonable value) = 1500 BTU * 1 hour * 0.293 Wh/BTU + 100 Wh = 539.5 Wh + 200 Wh = 739.5 Wh adjusted for carbon footprint.

The crockpot is the better option in all but the most optimistic oven scenario:

  • If there's a renewable component to the electric power, then the scenario improves for the crock.
  • If I bought a smaller crockpot, the scenario improves a lot for the crock pot.
  • If I always filled the oven when I used it (it's at least 4 times larger than the crock pot - remember it's a huge crock pot) the scenario improves a lot for the oven.
  • Let's be explicit that we are assuming that the carbon footprint of the power mining, generation, and transmission infrastructure for gas and electricity is identical.

One more gloss - is there a price difference between gas and electric power?

  • I get charged $0.12233/kWh, or $0.00012233/Wh.
  • I get charged $1.04579/Therm (a therm is 100,000 BTU), or $0.000010458/BTU. This is like paying $0.000035692/Wh - more than 3 times cheaper.

This makes the oven the cheaper option in the midpoint scenario as well. If we assumed (foolishly) that the difference in price between gas and electricity accurately reflects the difference in carbon footprint for the respective mining, generation, and transmission infrastructures then gas is probably your best choice.

Here's a table that summarizes all the scenarios:

scenario hours watts BTU/hour energy (Wh) adjusted energy cost
crockpot 2 270 0 540 1620 $0.07
oven, always on 1 100 30000 8890 9090 $0.33
oven, max reasonable 1 100 9000 2737 2937 $0.11
oven, midpoint 1 100 5250 1638.25 1838.25 $0.07
oven, min reasonable 1 100 1500 539.5 739.5 $0.03

crockpot versus oven.ods8.85 KB


Ovens can be a waste..

I've always seen our oven as a big energy waster and here's why. I live with my wife so there are only two of us in our household.

This means that we rarley utilize the whole of the space in the oven but all of that space still needs to be heated up. This is quite obviously aa big waste of a lot of energy.

We have two sized crockpots and now use the oven on vary rare occasions. I like to conserve energy where ever possible and talk about this on my website.

firebus's picture

Size doesn't matter

Luke, it doesn't matter if your oven is mostly empty, or if your crockpot is completely full.

If the oven uses less energy to cook the same amount of food, it's still more efficient.

You have to look at the numbers if you're really interested in conserving the most energy.

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