How much more efficient is a Washing Machine's Eco cycle?

I recently did some exploration of dishwasher power usage to see how Eco mode compared to Normal mode in terms of power consumption.

At the end I noted

I am curious to see whether the same holds true for the washing machine - our machine doesn't have an explicit Eco mode, but it does have a short-cycle

First, a correction: It turns out our washing machine (a Bosch Serie 4) does have an eco-mode, it's just not well marked.

As before, I'm using some Tapo P110s to meter usage, and writing the data into InfluxDB for easy analysis.

There are many, many more options on a Washing machine than a dishwasher - if I were to try and test them all, I'd still be at it next Christmas. So, I'm going to constrain myself to just a few

  • 60 Degree (centigrade) cotton cycle
  • 40 Degree cotton cycle
  • 40 Degree cotton cycle with eco mode enabled
  • 30 minute short-cycle (runs at 30c by default)
  • 15 minute short-cycle (runs at 30c by default)

To see how they compare.

The same load was used throughout - it was given a run through prior too to ensure it was soaking wet at the beginning of all runs (so that the first run didn't get a weight advantage by having dry clothes).

60 Degree cotton cycle

I think most people now understand that routinely washing at 60 is a massive waste of energy (in fact, the advice is now to go for 30 if possible), but I wanted to include a wash at 60 just to see how the energy usage compares.

The cycle lasts 2 hours 42 minutes

Full Cycle

There's a significant rise in consumption at the beginning of the cycle, with the heating element active for 22 minutes (with two 2 minute breaks in the middle).

Consumption then drops down to around 80W for 1h 11 mins, until the first short spin starts. The first three spins take usage to around 270W, whilst the final comes in at 430W.

The cycle consumed 1.12 kWh Full Cycle

The consumption value relies on a daily counter built into the smart plug, because the run ran past midnight I had to do a little bit of arithmetic in Flux to generate the graph above

// Consumption value in W before cycle was started
// allows us to reset to 0
before = 1906

from(bucket: "Systemstats/autogen")
  |> range(start: 2022-02-16T22:15:00Z, stop: 2022-02-17T01:15:00Z)
  |> filter(fn: (r) => r._measurement == "power_watts")
  |> filter(fn: (r) => r._field == "watts_today")
  |> filter(fn: (r) => == "washing-machine")
  |> map(fn: (r) => ({ r with _value:

     // Check if the point falls on/after midnight
     if r._time > time(v: "2022-02-16T23:59:59.99Z") then

          // Consumption at midnight was just over 1kWh
          // add that onto readings from the early hours
          r._value + 1004

          // Adjust so the value given ignores today's
          // earlier tests
          r._value - before

As well as adjusting readings so they start at 0, when midnight it comes, it starts adding the previous day's final reading on.

At £0.21/kWh the cost of the cycle is £0.24

40 Degree cotton cycle

The cycle lasts 2 hours 4 minutes

Full Cycle

Heating takes place at the beginning, but is fairly on/off, with drops in the consumption. The initial drops may be the result of a thermostat kicking in, but there's a period of 12 minutes between the penultimate and last spike - it seems likely the machine is periodically pumping a small amount of water out or similar.

Usage drops to around 80w until the end of the cycle, where the spin cycle brings usage up to around 300W

The cycle consumed 0.93 kWh Eco Cycle

At £0.21/kWh the cost is therefore £0.20

Eco mode cotton cycle @ 40 Degrees

The eco cycle lasts 3 hours 19 minutes

Eco Cycle

There's a single period of heating at the beginning of the cycle, lasting for 14 minutes.

The rest of the cycle sits at around 80w until the spins kick in, bringing consumption up to around 330W.

The cycle consumed 0.9 kWh Eco Cycle

At £0.21/kWh the cost is therefore £0.19

30 minute Short-Cycle

The short-cycle uses a 30 degree temperature by default - whilst prodding buttons though, I realised that you can drop it down to 20 or even 10 (something you can't do with the Cotton cycle).

The cycle lasts 30 minutes

Short Cycle

(I cropped the screenshot in the wrong place, it's easy to miss on the scale, but there's 2-5W of usage running for the remainder of the 30m).

Unlike the other cycles, there's no prolonged initial heating stage, with usage running between 21W and 133W for most of the cycle. Just prior to finishing, there's one burst up to 291W for the final spin.

The cycle consumed 0.02 kWh

Eco Cycle

At £0.21/kWh the cost is therefore £0.004

15 minute Short-Cycle

Again, this uses a 30 degree temperature by default.

Despite reporting 15 minutes on the display, the cycle actually draws power for over 20 minutes

15m Short Cycle

The initial stages of it's cycle use more power than the 30 minute version, with the lower sections being 40W rather than 20W. It doesn't see quite the same height of spike mid cycle, but the latter half again sees more usage than in it's longer running counterpart.

The final spin uses slightly less power (around 250W) than the longer cycle.

The runtime is odd, so I thought maybe I'd made a mistake and run the longer cycle by accident, but a second (more careful) run of the 15 minute cycle confirmed it - it definitely clocks in at a little over 20 minutes

15m Short Cycle

The cycle consumed 0.02 kWh

Eco Cycle

At £0.21/kWh the cost is therefore £0.004


In my previous post, I made a joke about this not being that interesting, but actually there are a couple of unexpected surprises here

  • ECO mode only uses marginally less power than the normal cotton spin
  • A 15 minute short cycle uses the same power as a 30 minute one
  • The 15 minute cycle isn't actually 15 minutes (I knew appliance clocks were lying to us!)

There're also some things that are less surprising, but interesting to put numbers on

  • Dropping the Cotton cycle temperature from 60C to 40C reduces power consumption by 17%
  • Using Cotton eco reduces consumption by 20% compared to 60C
  • A either short-cycle reduces consumption by 98% compared to 60C, and 97.8% compared to 40C

There could be some deviation in the graphs caused by my sampling frequency, but the overall/total usage comes from a counter within the Smart plug so should be as reliable as it's possible to get with this kit.

The 15 minute short cycle, in effect, uses double the power per minute used by the 30 minute cycle - presumably the drum tumbles at a slightly higher speed to try and offset the much shorter time clothes have to soak.

Eco mode does save some power - 300Wh across the cycle - compared to the normal 40C cotton run. But the run take almost 75 minutes longer (which is fairly inconvenient, especially if you need to get a few loads done).

The clear winner here, outside of heavy soiling, is the 30 minute short-cycle - even on the heat cycle it scores massive savings compared to the other programs because it's only heating water to 30c.

Using the typical figures from we can say that 1kWh equates to 0.1936KG of carbon emissions, so:

  • Normal @ 60 degrees: 0.22KG per run
  • Normal @ 40 degrees: 0.18KG per run
  • Eco @ 40 degrees: 0.17KG per run
  • 30m short cycle: 0.004KG per run
  • 15m short cycle: 0.004KG per run

What's also interesting here, is just how low those numbers are compared to the dishwasher.

Whilst both appliances heat and pump water, washing machines have the additional mechanical overhead of spinning a drum full of water and heavy clothes. I'd assumed that that would lead to much greater usage, but the washing machine heats water for a lot less time which gives it a serious edge.

Of course, the manufacturer is also quite relevant to this, despite the fact they've sorely misled us about the 15 minute program, Bosch's appliances do tend to be extremely power efficient, whereas the Dishwasher's manufacturer (Indesit/Hotpoint) doesn't have quite the same environmental creds.