How to Use the Radiator Calculator

1. Room Area (m²): Enter the floor area of the room you want to heat. For irregular rooms, calculate total floor area by multiplying length × width.
2. Room Height (m): Enter the floor-to-ceiling height of the room. This is used to calculate the room volume, which determines the total heat demand.
3. Heating Region: Select the climate zone that matches your building location. Each region corresponds to a different outdoor design temperature (e.g., Region 2 = −3 °C, Region 5 = −21 °C). Choose a colder region for a conservative, safe-side estimate.
4. Floor Position: Select where the room sits in the building. Roof-floor rooms lose more heat through the ceiling; basement rooms lose more through the floor. “Average” uses a balanced coefficient suitable for mid-building rooms.
5. Envelope Condition: Describe the thermal insulation quality of the room’s external walls and exposure to wind. “Uninsulated free” (exposed, no insulation) gives the highest heat-loss coefficient; “Insulated protected” gives the lowest.
6. Radiator Output (kcal/h/m): Enter the manufacturer’s rated heat output per metre of radiator at the standard 75/65 °C supply/return and 20 °C room condition. This value is found on the product datasheet.
7. Unit Conversion — Heat Load (kcal/h): Enter any heat load in kcal/h to instantly convert it to kilowatts (kW). This field is independent of the room-load calculation above.
8. Practical Radiator Capacity — Radiator Length (m) & Panel Height (mm): Enter the total length of radiators already installed (or planned) and their panel height. The calculator will show the installed capacity in kcal/h and kW.
9. Practical Radiator Capacity — Required Heat (kcal/h): Enter the known heat demand for the space (e.g., from a heat-loss calculation). The calculator will show how many metres of radiator are required at the rated output.
10. Reading the results: The main result card shows the Required Radiator Length for the room load calculated above. The metrics panel shows room volume, heat-loss coefficient, and heat load in both kcal/h and watts. The region table cross-references all floor positions and envelope conditions so you can compare scenarios at a glance.

How It Works

The Radiator Calculator uses the volumetric heat-loss method, a widely used simplified approach for residential and light-commercial radiator sizing. The room volume (area × height) is multiplied by a heat-loss coefficient (kcal/h per m³) that accounts for the climate zone, floor position, and insulation quality. These coefficients are drawn from standard Turkish heating engineering practice (TS 2164 / ASHRAE-equivalent tables) and are the same values embedded in the original YNS Mechanical Engineer workbook.

The reference condition for all radiator output ratings is 75 °C supply / 65 °C return / 20 °C room temperature (ΔT = 50 K), which is the European standard test condition (EN 442). Manufacturer datasheets always state output at this condition, so the calculated required length directly corresponds to standard catalogue values.

The unit conversion uses the exact thermodynamic relationship: 1 kcal/h = 1.163 W (equivalently, 1 kW = 860 kcal/h). This means a heat load of 1,000 kcal/h equals 1,163 W or approximately 1.163 kW.

The required radiator length is calculated as: Heat Load (kcal/h) ÷ Radiator Output (kcal/h/m). The installed capacity is: Radiator Output (kcal/h/m) × Installed Length (m) × Height Correction Factor, where the height correction accounts for the fact that taller panels radiate proportionally more heat per metre of width.

Frequently Asked Questions

How do I choose the correct Heating Region?

Select the region that corresponds to your city’s outdoor design temperature. In Turkey, Region 1 covers mild coastal zones, while Region 5 covers the coldest continental highland areas. If you are unsure, choose a colder region for a conservative (larger) result — it is always better to oversize radiators slightly than to undersize them.

What does “kcal/h/m” mean for Radiator Output?

It means kilocalories per hour per linear metre of radiator. For example, a value of 1,509 kcal/h/m means that every metre of that radiator (at 75/65/20 °C reference condition) delivers 1,509 kcal/h of heat, equivalent to approximately 1,756 W/m. This figure is always stated on the product datasheet and varies by panel height and type (Type 11, 22, 33, etc.).

Which Envelope Condition should I select for a typical apartment?

For a mid-floor apartment in a building with standard brick or concrete walls and no added insulation, choose Uninsulated free to be safe. If the external walls have been retrofitted with insulation boards (e.g., EPS/XPS facade system), choose Insulated free. The “protected” variants apply to rooms that are sheltered from wind on the exposed side (e.g., an interior courtyard).

How do I use the Unit Conversion section?

Simply type any heat-load value in the Heat load (kcal/h) field and the converted power in kilowatts appears instantly in the result panel. This is useful when your boiler or heat-pump is rated in kW and you need to cross-check against a kcal/h design figure, or vice versa.

What should I do if the Required Radiator Length is longer than what is installed?

You have three options: (1) Install additional radiator panels in the room to meet the calculated demand. (2) Upgrade to a taller or higher-output radiator type (e.g., switch from Type 11 to Type 22) to increase output per metre. (3) Improve the room’s insulation or draught-proofing to reduce the heat load — then re-run the calculation. Never reduce the heat load figure artificially; undersized radiators result in a cold room on the design-day.

Is this calculator suitable for underfloor heating or fan-coil units?

No. The output rating field is specific to panel radiators at the 75/65/20 °C reference condition. Underfloor heating systems operate at much lower water temperatures (typically 35/30 °C) and use different sizing methods. Fan-coil units are sized by airflow and coil characteristics. Use this calculator only for conventional panel or sectional radiators.

Can I use this calculator for commercial or industrial buildings?

The volumetric coefficients used here are calibrated for residential construction. For commercial buildings with large glazing areas, high ceilings, or significant ventilation loads, a full heat-loss calculation per EN 12831 or ASHRAE 2009 is recommended. This calculator can still provide a useful first-pass estimate for small commercial spaces, but should not replace a detailed engineering calculation for critical projects.