Estimate tool
Boiler kW calculator
This page is a free tool that estimates how many kW of combi boiler an apartment or house in Antalya needs. The result is a simplified heat loss calculation and does not replace an engineering project.
Estimate your heat load and the matching combi boiler capacity in seconds. The tool uses your district climate zone, floor area, ceiling height, insulation, floor position, number of external walls and number of bathrooms.
Result
Fill in the form and press “Calculate”; the result appears in this area.
This is a preliminary estimate; the final appliance and radiator selection is made during a free site survey.
How we calculate
The heat load is the product of area × base W/m² × climate × ceiling × floor × external walls. The base W/m² value comes from the insulation level. The result is divided by 1000 to give kW.
A 10–20% safety margin is added to that heat load to give the recommended boiler capacity range. The number of bathrooms does not change the heating capacity; it sets the lower limit for domestic hot water: 24 kW and above is recommended for two bathrooms in simultaneous use.
The base W/m² values are heating-industry practice, not a certified standard clause. The climate factor is derived from TS 825 Annex 4 (degree-day zones) and Annex 2 (monthly mean outdoor temperature by zone). An exact project requires a room-by-room heat loss calculation to TS EN 12831.
Coefficients used
| Coefficient | Value |
|---|---|
| Yes (insulation + glazing) | 80 W/m² |
| Partial (glazing only) | 110 W/m² |
| None (older building) | 135 W/m² |
| Coefficient | Value |
|---|---|
| 2.60 m (standard) | × 1.00 |
| 2.80 m | × 1.08 |
| 3.00 m and above | × 1.15 |
| Coefficient | Value |
|---|---|
| Middle floor | × 1.00 |
| Top floor (under the roof) | × 1.12 |
| Ground floor | × 1.12 |
| Detached house / villa | × 1.22 |
| Coefficient | Value |
|---|---|
| 1 external wall | × 1.00 |
| 2 external walls (corner) | × 1.08 |
| 3 or more external walls | × 1.15 |
| Coefficient | Value |
|---|---|
| Antalya (TS 825, 1. zone) | × 1.00 |
| Korkuteli (TS 825, 3. zone) | × 1.55 |
Worked example
Muratpaşa, 120 m², insulated middle floor, 2 bathrooms
| Area | 120 m² |
|---|---|
| Base value (insulated) | 80 W/m² |
| Climate (Antalya, zone 1) | × 1.00 |
| Ceiling 2.60 m | × 1.00 |
| Middle floor | × 1.00 |
| 2 external walls | × 1.13 |
| Heat load | 10.8 kW |
| Safety margin 10–20% | 11.9 – 13.0 kW |
| Hot water minimum (2 bathrooms) | 24 kW |
| Conclusion | Heating needs only 12–13 kW; hot water is the deciding factor. A boiler with 24 kW or more hot water capacity is selected. |
Why bigger is not always better
A boiler far above the real demand meets the heat load quickly and then keeps stopping and re-igniting. This short cycling wears the heat exchanger, lowers efficiency and makes room temperature swing. The right choice is the smallest suitable appliance 10–20% above the calculated heat load. Vaillant modulating boilers (1:7 to 1:10) reduce the effect at part load, but they do not fully compensate for a wrong capacity choice.