Understand your estimate
How to use this result
Price a water heater from measured or declared electrical energy, actual resistance-element on-time, or a clearly bounded resistance-heating scenario. Purchased electricity, useful water heat and stored-water losses have different boundaries.
Method reviewed · Calculation methods · Evidence and source policy
Find the right inputs
Electrical source
Measured kWh/days or declared electrical kWh/year
Keep draw profile, climate, operating mode and meter boundary with the figure.
Resistance alternatives
Actual input kW/on-hours or volume/temperature rise
A timer window is not necessarily element-on time; the volume scenario does not model heat-pump efficiency.
Losses and tariff
Explicit additional electrical losses and currency/kWh
Measured or declared input already contains losses within its boundary; never add them again.
The calculation
Measured input: sample kWh ÷ complete days × use days. Annual declaration: annual electrical kWh directly. Simplified useful heat = litres × temperature rise in °C × 4.186 ÷ 3,600; divide by resistance conversion fraction and add only explicit extra electrical losses.
A worked arithmetic example
Illustrative arithmetic: 42 electrical kWh over seven complete days average 6 kWh/day. Projected onto 30 use days at $0.20/kWh, that is 180 kWh and $36. The figures are a selected arithmetic sample, not an observed household test.
What the estimate can tell you
The thermal mode assumes liquid-water density 1 kg/litre and fixed heat capacity 4.186 kJ/(kg·°C). Temperatures describe the task, not a recommended thermostat setting. The tool does not design installations, size tanks or infer heat-pump COP.
Questions about this calculation
Can I price a heat-pump water heater here?
Yes with compatible measured or declared electrical consumption. Do not use the resistance-only volume scenario to infer compressor efficiency or backup-element operation.
Are standing losses added to my measured kWh?
No. The reading already contains electricity inside its meter boundary. Only the simplified resistance scenario has an explicit extra electrical-loss allowance.