For appliances used daily over a decade, running cost frequently exceeds purchase price. Energy labels exist to make this visible and they measure specific things under specific conditions.
What the label states
Generally an efficiency class on a scale, plus an annual consumption figure in kilowatt hours, plus category-specific measures.
The annual figure is calculated from a standardised test cycle and an assumed number of uses per year.
Which makes it comparable between products and not a prediction of your bill, since your usage will differ from the assumption.
The comparison is the point. The absolute figure is an illustration.
The test cycle question
Where the figures diverge from real use.
Testing uses a defined programme, generally the one designated as the reference cycle, at a specified load.
Real households use different programmes, at different loads, at different frequencies.
Which means a machine optimised for the test cycle may perform less well on the programmes people actually use, and this has been a documented issue across several appliance categories.
Regulations have been revised repeatedly to address it, including rescaling of the classes to remove the accumulation of top grades.
The rescaling
Worth knowing because it causes confusion.
Classes were rescaled in some regimes, so a product that would previously have carried a top grade now carries a middle one without any change in performance.
The purpose was to restore headroom, since nearly everything had accumulated at the top of the old scale.
Which means comparing a label from before and after the change is meaningless, and a middle grade under the new scale may be genuinely efficient.
Calculating your own cost
Straightforward and more useful than the class.
Take the annual consumption figure, multiply by your electricity rate, and adjust for how your usage compares to the assumed one.
Over a ten year life, compare that total against the purchase price difference between two models.
Frequently the more efficient model pays for itself within a few years, and occasionally it does not, particularly where the price gap is large and the usage is light.
Doing the arithmetic rather than assuming is the whole point of the label existing.
Where running cost dominates
The categories worth calculating.
Refrigeration, which runs continuously and where the difference between classes accumulates substantially.
Heating and water heating, which are the largest household energy uses by a wide margin.
Washing and drying, particularly tumble drying, where heat pump machines cost more and use substantially less.
And lighting, where the transition to efficient sources has already delivered most of the available saving.
Where it does not
Categories where the label is less consequential.
Anything used briefly and occasionally, where the annual consumption is small regardless of class.
Small appliances generally, where the absolute consumption is low.
And devices where standby consumption dominates, which has been substantially reduced by regulation and is now a small figure.
The water dimension
Which appears on labels for relevant categories and is frequently ignored.
Washing machines and dishwashers state water consumption per cycle, and where water is metered this is a real cost alongside energy.
Modern machines use dramatically less water than older ones, which is a genuine improvement and one of the stronger arguments for replacing a very old machine.
The repair versus replace calculation
Where the running cost figure is actually decisive.
An old inefficient appliance that fails presents a choice, and the running cost difference over the remaining life is the number that resolves it.
For a very old refrigerator or a very old heating system, replacement frequently pays back quickly.
For a relatively recent machine with a modest efficiency gap, repair is generally better, both financially and in terms of the embodied energy in manufacturing a replacement.
That last consideration is real and is absent from every label, which measures use rather than production.
Standby and the small loads
Worth a note since it is widely misunderstood.
Standby consumption has been substantially reduced by regulation and is now a small figure for most devices.
Which means the traditional advice to unplug everything delivers a much smaller saving than it once did.
The exceptions are older equipment, devices with external power supplies that run warm, and anything with a display or a network connection permanently active.
Measuring with an inexpensive plug-in meter resolves it for a specific household, and it generally reveals that the large loads dominate entirely.
The tariff matters as much as the appliance
A point that is frequently larger than any efficiency difference.
Time-of-use tariffs price electricity differently through the day, and shifting high-consumption activities into cheaper periods can produce savings exceeding the difference between efficiency classes.
Appliances with delay timers make this straightforward for washing and dishwashing.
Which means the combination of a reasonable appliance and a suitable tariff frequently beats a more efficient appliance on a flat rate, and the tariff costs nothing to change.