Toaster Power - One or Two Rounds of Bread?

The all important question addressed by this page, is whether a two slot toaster will use less power if it toasts one round of bread rather than two.

At some point in time I will document the setup, but for now just take it for read that our Raspberry Pi monitors the amount of electrical power consumed by the house, and uses Apache to serve up consumption plots via a web browser page.

Observation 1 - Power

The plot below is extracted from today's comsumption plot, and shows the steady state power consumption of the house, with three times of increased consumption:

  1. The toaster cooking two rounds of bread (with two 10 seconds uses of the microwave in the same period),
  2. The kettle being boiled with sufficient water to make one mug of coffee, and
  3. The toaster cooking one round of bread.
Toaster Power Consumption

The thing to note here, is that the level of power (the height of the graph) used by the toaster when cooking two rounds of bread is, to within the accuracy of the equipument used for this experiment, the same as the level of power used for cooking one round. So, broadly speaking, it appears that if you intend to cook one round of bread in a two slot toaster, there will be no additional power used to cook a second round at the same time.

To put it another way, if you intend to toast two rounds of bread, then you will use roughly half the electrical energy if you toast both rounds at the same time, rather than separately.

Observation 2 - Energy

Inspecting the above graph a second time, one might note that the second use of the toaster involved the use of slightly less energy. The power used was the same (same height of the bar), but the energy used was slightly less as the toaster was not on for quite as long (the second toasting bar was not quite as wide as the first).

The slightly reduced toasting time for the second toasting is a result of the toaster retaining some heat from the first toasting. Second and subsequent toastings will therefore use slightly less energy than an initial toasting.

What I did not mention above, is that our toaster is a four slot toaster, with two pairs of two slots. Either pair of slots can be used on their own, or both pairs can be used at once. Observation 2 would suggest that if cooking more than two rounds of bread, slightly less energy will be used if one reuses the same pair of toaster slots multiple times, rather than employing all four slots.


"Your mileage may differ", results drawn from toastings using our toaster do not necessarily mean that your toaster will behave in the same manner.

No baked beans were injured in the conducting of this experiment.