If my 120 volt toaster oven draws 14 amps on high & my oven draws 12 amps on high, which one would use less electricity to bake a pizza?

Question

An article from my AARP magazine suggests using a toaster oven vs a regular full size electric oven to bake a pizza, make a dinner, bake a pie, etc because it would use about half of the electricity so save on the electric bill. Problem is, The toaster oven draws 14 amps in the bake mode and my oven draws only 12 amps per leg (220) while the elements are on. How do they suggest that I will cut the electric power in half when the full size oven uses 2 amps less than the small 120 volt toaster oven?

Answer 1

The actual power consumption is Watts, not Amps. Watts, for a resistive load such as an oven (toaster or full-size, but not microwave) is essentially Volts x Amps. So the comparison is really:

• Toaster = 120V x 14A = 1,680 Watts
• Full-Size Oven = 240V x 12A = 2,880 Watts

If they take the same amount of time, and if they both run at full power levels the entire time, then the toaster oven will use approximately 58% as much as electricity as the full-size oven. Not exactly 1/2, but pretty close.

There are a few other things to consider:

• If you use an oven for more than a few minutes then it will cycle on/off to maintain the set temperature. If the toaster runs at a 75% duty cycle and the regular oven at a 50% duty cycle then the toaster will use 87% as much power as the full-size oven. If the toaster runs at a 50% duty cycle and the full-size oven runs at a 75% duty cycle then the toaster will use 39% as much power as the full-size oven. etc.
• Baking Time - In theory any two ovens that can maintain the desired temperature should take about the same time to bake a given item. However, the time to get to the desired temperature (preheat) may vary significantly between ovens.
• Insulation - A modern full-size oven should be well insulated, so that relatively little of the heat gets into the kitchen, although obviously all the residual heat after baking is done will eventually get into the kitchen. But good insulation and design will mean the oven can keep the heat inside better, both lowering the duty cycle and lowering the amount of energy wasted heating up your kitchen. In the winter this is not necessarily a problem, but in the summer any extra heat will either make the kitchen more uncomfortable or increase your air conditioning load. Toaster ovens typically have very poor insulation.

The specifics will vary a lot depending on the specific ovens. But in general I would expect a toaster oven to be more efficient on the small stuff (e.g., making toast, reheating pizza, etc.) where the duty cycle on any oven will likely be 100% and where the overall time of use means the extra heat from a poorly insulated oven will not have that much of an effect on the kitchen. But on the big stuff (e.g., baking a pie) the duty cycle will likely favor the big oven and the overall time plus variation in insulation (full-size oven normally being significantly better than toaster oven) will favor the full-size oven.

And unless you are running a bakery, most of your energy costs are likely to be:

• HVAC
• Water Heating
• Lighting (though less than it used to be thanks to LEDs, can still be significant if lights are on a large part of the time)

with cooking generally one of the smaller components with large intermittent usage (peak demand) but low total cost.

Update: After some interesting and thoughtful comments, I looked a little more. While everyone's individual home usage will vary depending on age of home, type of appliances, sources of energy, weather, etc., a rough guide from the U.S. Energy Information Administration (EIA) has the top residential electricity uses as:

• Air Conditioning 17%
• Space Heating 15%
• Water Heating 14%

(In terms of total energy usage, space heating and water heating are probably much higher because many homes use natural gas or other fossil fuels.)

Lighting is next at 10%, though that was a 2015 number so I am sure it has been decreasing thanks to the rapid adoption of LED lighting.

Cooking is way down on the list at 1.4%, lower than refrigerators, TVs and some other things. Even if you combine microwaves, cooking is only 2.5% of the total, and you can't use microwaves (practically) to bake a pizza.

So if you can save 50% on electricity use with a toaster oven compared to a full-size oven (of which I am dubious in general, but each situation will vary), for most people it will not be large enough to be practical for everything (chicken nuggets, OK; Thanksgiving turkey, not so much), and it is only part of "cooking" (there is also the stove top for boiling, frying, etc.). So only a small part of the 1.4% will be saved, and likely at some inconvenience as well, depending on usage.

Yes, every little bit helps. But if you still have incandescent bulbs, replace them (immediate easy savings). If you have old HVAC equipment, consider replacement (not so easy and significant up-front cost, but huge long-term energy savings).

Answer 2

You might be getting confused by North American split-phase power, which is quite a headful.

The answer is, North American homes get 120V... but twice. The two banks are opposite-phased, so they can stack to 240V.

The toaster oven draws one bank of 120V... you are drawing 14A off one bank. The range draws both banks of 120V @ 12 amps, and you need to pay for 12 amps off both banks - i.e. you are drawing 12 amps twice.

You could call it 24A for billing/comparison purposes... but it's actually 12A at twice the voltage.

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If your quibble is how the toaster oven draws slightly more at 14A vs 12A, well... the oven being 12A is random*. The toaster oven being 12A is expected. Most plug-in appliances in North America have maximum "1500 watts", because that is all UL will approve. UL assumes 125V since voltages often exceed 120V - 125V gives 12 amps. 12 amps is exactly the plug-in appliance limit on a 15A circuit, per NEC 210.23(A)(1) (plug-in appliances can't exceed 80%). Of course, with unregulated, non-complying foreign goods sold direct-mail, all bets are off.

* Well, not entirely random. The "80% of circuit ampacity" mentioned later in the paragraph applies to hardwired loads too, so the 12A oven is sized just right to be on a dedicated 15A circuit.

Answer 3

The answer to this depends partly on what you mean by "bake pizza".

Baking a pizza really well from scratch requires stored energy and high temperature, hence people use pizza bricks or pizza ovens. If you do it that way, your toaster oven is probably not capable. If you try to heat bricks in it, you'll lose a lot more energy due to its relatively poor insulation. In fact, the bricks may never fully heat up for the same reason.

On the other hand if what you're doing is reheating a frozen pizza or just melting a slice of cheese on a slice of bread, the toaster oven may be more efficient since the toaster's heating elements are acting directly on the food, not heating up the oven itself as much and more importantly, not preheating the substantial metal casing of the larger oven.

Answer 4

I have a very simple answer for this.

P = V * I If you are looking for power consumption we can calculate it as so:

Oven: P = 240V * 12A = 2880 W

Toaster: P = 120V * 14A = 1680 W

We will assume that these take the same amount of time which implies that the Toaster is a better power consumption rate.

A more advanced answer is that we can assume the pizza will take 15 minutes to make and the toaster takes 1 minute to heat up whereas the oven takes 10 minutes. The units for power is W and that is equal to Joules/second. We will assume that the toaster needs 16 minutes and the oven needs 25 minutes.

oven energy: E = 2880 J/s * 25 min * 60s/min = 4320000 J or 4320 kJ

Toaster energy: E = 1680 J/s * 16 min * 60 s/min = 1612800 J or 1612.8 kJ

The toaster takes 3 times less energy to make a pizza.

If you have different oven specs, feel free to just recalculate these values.