A longer wash could cost less, even at peak prices

French households with an affected peak/off-peak electricity plan deciding whether to shorten a dishwasher cycle to fit a changed cheap period.

Mainland France within the stated reform. The numerical example uses one Bosch model and one EDF tariff, not all homes or machines.

A household may avoid a more expensive quick cycle without buying equipment.

A poorly matched programme, extra wash, missed deadline or unsafe schedule can outweigh a small electricity saving.

When a supplier notice changes a household’s cheap hours, or when comparing a long cycle with a shorter one that fits the window.

quantified

For unchanged cycle energy, its electricity cost is off-peak kWh times the off-peak price plus peak kWh times the peak price. Comparing an all-peak Eco cycle with an all-off-peak quick cycle gives a conservative bound.

Let E be Eco kWh, Q the alternative’s kWh, H the peak price and L the off-peak price, with H greater than L. Eco is cheaper even entirely at peak if E × H < Q × L, equivalently E/Q < L/H. At the cited prices L/H is 0.74183, so an energy reduction greater than about 25.82% is enough for that bound.

If x is Eco kWh charged at peak and the alternative is wholly off-peak, the exact condition is x < L × (Q − E)/(H − L). x is energy, not hours. Equality gives the same electricity cost.

Use the actual effective schedule and current contract. The August tariff is a dated input, not a promised future price.

The example gives €0.155295 versus €0.190680, a difference of €0.035385 per cycle in the conservative comparison. That is modest. Do not turn it into a household or annual saving without actual cycles and energy use. Standing charges do not change between two cycles on the same contract. Water, detergent, cleaning result, extra washes and time constraints also matter.

No appliance purchase, company valuation or investment recommendation.

If the all-peak bound fails, it does not prove Express is cheaper. Compare actual energy across the windows. If Eco also fits safely within a cheap window, that can be better still. A genuinely lower-energy short programme can reverse the ranking.

Read the supplier’s notice and the exact appliance manual. Compare two programmes that can clean the same load. Multiply Eco’s full-cycle kWh by the peak price, and the alternative’s full-cycle kWh by the off-peak price. If the first is lower, Eco beats even that favourable timing for the alternative under those inputs.

If not, do not guess from duration: use available programme or safe consumption data for each price window, or retain a suitable schedule without claiming a saving. Also check whether Eco can fit in another safe cheap period. Stay awake and able to respond, follow the manufacturer’s instructions, and let the selected cycle finish.

When the household’s notified schedule changes, and when its tariff or appliance programme changes.

This is a no-purchase comparison using existing documents. Do not fit improvised timers, interrupt power to force a tariff split, or dismantle equipment. Seek qualified help if measurement would require electrical work. Water, detergent, repeat washing and availability of clean dishes belong in the final choice.

A different tariff, self-generated electricity, unsuitable load, urgent completion need, faulty appliance or unsafe operating period makes the comparison inappropriate.

Selectra’s 23 August article already compares this Bosch model’s programmes at a common price and recommends off-peak use. An October Moins Dépenser guide also stresses full-cycle cost, cleaning suitability and actual hours. The added analytical step is the conservative cross-tariff comparison and exact crossover condition during the current schedule migration. No global-first or general Eco-discovery claim is made.

Short does not always mean energy-hungry, Eco is not suitable for every job, and laboratory values need not match actual use. Different tariff spreads can change the answer.

Keep Eco within another safe cheap period, use a suitable short cycle when time matters, or leave the programme unchanged if the saving is too small to matter.

The numerical example does not apply when its model, programme energy, tariff or safe-use assumptions differ. The general inequality remains a calculation rather than a prediction of realised savings.

The policy, manufacturer, tariff and safety sources serve different roles. The two ADEME pages are one organisation. The numerical example is not independently measured, and no heating profile is invented. Dates refer to policy updates, tariff effectiveness or page revisions as stated. Exact publication clocks are unavailable. Sources are linked and factually paraphrased, not reproduced.