The simplified formula
In principle, annual electricity use is the useful thermal energy required by the building divided by the seasonal efficiency of the system. If a home requires 18,000 kWh of useful heat during a season and the system operates at a SCOP of 3.6, theoretical electricity use is around 5,000 kWh. Real operation is also influenced by domestic hot water, defrost cycles, auxiliary pumps and user behaviour.
Why two homes of the same size can use very different amounts of energy
A well-insulated 150 m² home can require much less heat than an older 150 m² building. Heated volume, insulation, air leakage, indoor temperature and outdoor design temperature can radically change the result. This is why a simple “X kW per Y m²” rule is insufficient for both sizing and consumption estimates.
Water temperature is critical
Underfloor heating normally operates at lower water temperatures and allows a heat pump to work more efficiently. Conventional radiators may require higher supply temperatures, particularly during cold weather. A heat pump being capable of producing high-temperature water does not mean that continuous operation at the maximum temperature delivers maximum efficiency.
Domestic hot-water consumption
Domestic hot water is separate from space heating. The number of occupants, cylinder volume, set temperature and daily hot-water use influence the required energy. The ECO-TEC calculator estimates this component separately.
Heat pump and photovoltaic panels
PV can reduce electricity purchased from the grid, but annual totals must be interpreted carefully. Solar production peaks in summer while heat-pump electricity demand peaks during the heating season. Equal annual kWh figures do not automatically mean a zero bill; self-consumption, compensation rules and storage matter.
Why the ECO-TEC calculator shows a range
A useful estimate should not claim precision that the available inputs cannot support. The calculator combines calculated heat demand, equivalent operating hours and an indicative SCOP range for the selected emitter system. The result is suitable for comparison and budgeting, but it is not a detailed energy audit.
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