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Which heat pump is right for your property
The calculation uses real capacity tables for Exinda R290 units, rather than nominal ratings. The difference is critical: a heat pump rated at 12 kW delivers around 6 kW when outdoor temperatures drop to -15 °C, and unit selection is based on this performance.
How we calculate heat losses
The required heating capacity is calculated by multiplying the heated floor area by specific heat loss values, which depend on insulation level and the differential between indoor temperature (20 °C) and local winter design temperature, with ceiling height correction.
| Insulation | -12 °C | -15 °C | -18 °C |
|---|---|---|---|
| New construction | 26 | 28 | 30 |
| Well insulated | 44 | 48 | 52 |
| Partially insulated | 68 | 75 | 81 |
| Uninsulated | 119 | 130 | 141 |
Specific heat loss in W/m² of heated area, at 20 °C indoor temperature.
Why nominal capacity is not winter capacity
Under standard EN 14511, heat pump ratings are specified at +7 °C ambient air and 35 °C flow temperature. At -15 °C, the same unit delivers approximately half of that capacity. These values are not estimates - they are extracted directly from Exinda technical submittal data sheets.
| Model | +7 °C | +2 °C | -7 °C | -15 °C | remaining |
|---|---|---|---|---|---|
| 6 kW | 6.8 | 5.9 | 4.4 | 3.3 | 48 % |
| 9 kW | 9.1 | 8.0 | 6.2 | 4.8 | 52 % |
| 12 kW | 12.1 | 10.6 | 8.0 | 6.2 | 52 % |
| 15 kW | 16.5 | 14.3 | 11.2 | 9.0 | 54 % |
| 20 kW | 22.9 | 20.0 | 15.9 | 12.1 | 53 % |
Available capacity in kW at 35 °C flow water temperature. The last column shows the capacity retention at -15 °C relative to +7 °C.
Where the design temperature comes from
The winter design temperature is neither the absolute coldest temperature ever recorded nor the seasonal average. It is a standardized engineering benchmark. Building energy regulations classify climate zones where design temperatures reach down to -15 °C or lower. Novi Sad and most of Vojvodina use -15 °C as the statutory reference for heating projects and subsidy applications.
This does not mean outdoor temperatures stay at -15 °C throughout winter. A typical heating season lasts approx. 4,400 hours, with the vast majority spent between 0 °C and +7 °C. Temperatures drop below -7 °C for only about forty hours per year. Sizing a heat pump to meet the absolute extreme solely on compressor power would result in an oversized unit that short-cycles most of the season and incurs higher operating costs.
Instead, the optimal heat pump satisfies the continuous seasonal load efficiently, while during extreme peak hours the integrated backup heater in the buffer tank supplements capacity. In annual energy balance, this backup accounts for less than two percent of total consumption, while saving substantially on initial equipment investment.
How we calculate savings
The seasonal coefficient of performance (SCOP) is computed from actual COP values across Exinda operating tables, weighted against the distribution of heating hours across temperature bins throughout the heating season. This bin method also yields total annual heating demand and electricity consumption.