A powerful appliance used briefly can cost less than a small load left running all day. Before replacing equipment or chasing every standby light, spend a week finding which changes matter in your household. The diary below is an original planning exercise; its example readings are fictional, not results from a tested home.
Download the blank appliance diary (CSV). Open it in your spreadsheet app or copy the headings onto paper. You do not need to upload a bill or share any account details.
Start with energy, not the power rating
Watts describe power at a moment; kilowatt-hours describe energy over time. A device drawing a constant 100 watts for 10 hours uses 1 kWh. A nameplate usually gives a rated or maximum power, so it is not a reliable measurement of a fridge cycling on and off.
SEAI describes plug-in monitors as a way to measure individual appliance consumption. Use only equipment suitable for the appliance’s load and follow both manufacturers’ instructions. Do not open electrical panels or attempt to meter a hardwired shower, cooker or heating system with a plug-in adaptor. For those, use existing monitoring or a qualified installer.
Your seven-day sequence
| Day | What to record | What you learn |
|---|---|---|
| 1 | Your tariff’s VAT-inclusive unit rate and the appliances to investigate | Which rate belongs in the calculation |
| 2–3 | One complete normal cycle for a suitable plug-in appliance | kWh per cycle rather than its peak wattage |
| 4 | A longer observation of a cycling appliance | Why a brief reading can mislead |
| 5 | Frequency of use across the household | Whether a large per-cycle cost is frequent enough to matter |
| 6 | One comparable alternative cycle or setting | The change in kWh, with load and conditions noted |
| 7 | Costs and practical changes you can sustain | A short, ranked action list |
Keep essential refrigeration, ventilation and medical equipment operating as intended. The exercise is observation, not a challenge to turn everything off. Choose energy-saving settings that still do the required job.
Worked example: prioritise the larger opportunity
Assume a flat 30c/kWh, purely for illustration. Appliance A uses 1.2 kWh per cycle, four times a week. Its estimated annual cost is 1.2 × 4 × 52 × €0.30 = €74.88. A comparable setting using 0.8 kWh would cost €49.92, a difference of €24.96 a year if the frequency stays the same.
A separate constant 5-watt load consumes 0.005 × 24 × 365 = 43.8 kWh, costing €13.14 a year. Eliminating it entirely would save less than the example cycle change. Neither figure justifies a costly replacement on its own.
These are marginal energy costs. Your standing charge does not disappear when you reduce an appliance’s use. If a cycle spans two price windows, split its measured consumption between them; multiplying everything by the cheapest rate exaggerates savings.
Avoid three misleading conclusions
One cycle is not an annual measurement. Load size, room temperature and selected programme affect consumption. Repeat the comparison before annualising a small difference.
A lower bill is not proof of lower consumption. A new tariff, credit or estimated reading can change the amount due. Compare kWh and rates separately.
Moving use is not the same as reducing use. A cheaper window can reduce cost without changing kWh. Use the tariff calculator to see whether the whole plan still works after standing charges.
Finish with one or two changes you can repeat and a date to measure them again. Record uncertain readings as uncertain; a small honest diary is more useful than a precise-looking annual saving based on guesses.
