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The counter-intuitive result, confirmed repeatedly in comparative studies: a full modern dishwasher on eco beats almost all hand washing on water AND usually on energy: the machine washes in 10-12L where a running tap pours that every 90 seconds. The caveats that keep it honest: only when FULL (half loads halve the advantage), eco mode not intensive, no pre-rinsing (scrape, don't rinse: the machine was designed for it), and the disciplined two-bowl hand washer basically ties: the running-tap washer funds the machine.
What The Dishwasher vs Hand Washing Calculator Works Out
- Dishwasher (eco, full load): a modern machine on its eco cycle washes a 12-place load in 10L to 14L of water and 0.8 kWh to 1.0 kWh of electricity, under 30p all-in at the current Ofgem price cap unit rate. It recirculates a small heated reservoir under pressure rather than drawing fresh hot water, which is the whole trick.
- Your sink method: the hot water cost of hand washing. A running hot tap lands near 80L and over 50p a session with gas-heated water at the current Ofgem cap rate; a disciplined two-bowl washer uses around 40L and under 30p, close to parity with the machine.
- Verdict: the per-session difference multiplied by sessions a week and 52 weeks. The tap-runner saves around GBP 100 a year at seven sessions a week and funds the machine; the bowl disciplinarian ties on money and loses only the evening half-hour.
- Dishwasher cost per load (advanced): edit the default (0.9 kWh at the current Ofgem cap unit rate plus 10L of metered water) for your own machine and tariff: an intensive cycle uses roughly 50% more energy than eco, despite the eco programme running longer. Duration-equals-cost is exactly backwards here.
- Tablets, salt and rinse aid (advanced): consumables add 10p to 15p a cycle to a complete account and are added to the machine's per-load cost.
- Loads you run half full (advanced): a half load costs a full cycle but does half the washing, so the share of half-full loads raises the machine's effective cost per session. Running full is the biggest single caveat.
- Dishwasher and hand washing per year (advanced): each method's total annual running cost at your number of sessions.
- Hours of your evening saved (advanced): sessions a year multiplied by minutes per hand wash. Seven 25-minute sessions a week is over 150 hours a year; put a value on your time and the card prices it.
- Payback on the machine (advanced): the purchase price divided by the yearly running-cost saving plus any time value. Skip the pre-rinse ritual too: it pours a hand-wash's worth of hot water before the machine starts, and modern detergent enzymes are designed to feed on food residue.