Heat pump calculator
How big a heat pump does your house need? Enter the floor area, insulation and town. We use the real winter of your area, not a national average.
Winter in Mostar and winter in Sarajevo are not the same. The design temperature comes from your town's climate.
The coldest 1 % of winter nights in Čitluk. If you have a design, enter your own.
The whole house: all the rooms you heat, together.
Heating capacity needed
4.9 kW
Heat loss of the house 4.87 kW at −6 °C, that is 41 W/m².
Compare with the heat pump's output at −6 °C from the manufacturer's table, not its nominal capacity (A7/W35). Every heat pump gives less in the cold.
Models that cover the need by the manufacturer's table
We compare the house's heat loss, 4.87 kW at −6 °C, with the heating capacity from the manufacturer's table: the row at that outdoor temperature or the first colder one, the column for water at 35 °C. Each model shows the row we took.
Bigger models, including those with a built-in hot water tank, are not listed: a smaller one covers the need by the manufacturer's table.
The capacities are from the manufacturer's tables (Fujitsu General, design & technical manuals): the unit's maximum capacity at that outdoor and water temperature. The certified data (HP KEYMARK) is on each model's page.
Winter: Čitluk
- −6.1 °C
- Coldest 1 % of nights
- 4 °C
- January average
- 52
- Frost days per year
Climate data: ERA5 (Copernicus) via Open-Meteo, 2010-2024.
An indicative estimate from floor area and insulation. We confirm the exact capacity with a free site visit and calculation.
How we calculate
The specific heat loss in watts per square metre of heated floor area depends on the insulation and on how cold it gets outside. The table is for 20 °C indoors; between the columns we interpolate. We multiply by the floor area, add 15 % for radiators because they need hotter water, and count 45 L of tank per person for hot water.
| Insulation | W/m² at -15 °C | W/m² at -10 °C | W/m² at -5 °C | W/m² at 0 °C |
|---|---|---|---|---|
| None | 120 | 102 | 84 | 66 |
| Poor | 95 | 81 | 67 | 53 |
| Average | 55 | 47 | 39 | 31 |
| Good | 40 | 34 | 28 | 22 |
| Low-energy | 22 | 19 | 16 | 13 |