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Panel Radiator Selection
System parameters
Room 1
Panel radiator sizing calculator per PN-EN 442
Professional panel radiator sizing calculator for central heating systems. Automatically converts nominal radiator power (75/65/20 °C conditions per PN-EN 442) to actual power for any operating parameters — from classic 80/60 °C to low-temperature heat pump systems at 55/45 °C.
A tool for HVAC designers, installers, and building owners. For each room, simply enter the heat losses and the calculator will select the minimum radiator length of the chosen type and height to cover the heating demand. Results can be saved to a project and exported as PDF.
How to use the calculator in 3 steps
Set system parameters: supply and return temperatures. The calculator will automatically compute the correction factor φ based on the logarithmic mean temperature difference relative to nominal conditions 75/65/20 °C.
Add rooms: for each one enter heat losses Q [W] (from building heat load calculations) and room temperature, then select the radiator type (10, 11, 21, 22, 33) and height.
Read the result: the calculator will show the minimum radiator length [mm] from the standard series that covers the room's heat losses at the selected operating parameters. The power reserve percentage is also displayed.
What the radiator sizing calculator computes
The program determines all parameters needed to correctly order a radiator from the manufacturer:
- φ — radiator power correction factor, accounting for the difference between nominal parameters (75/65/20 °C) and actual system operating parameters.
- Q_required — radiator power needed to cover the room's heat losses at actual operating parameters.
- L_min — minimum radiator length from the standard series (in 100 mm increments) whose actual power ≥ room heat losses.
- Power reserve [%] — the percentage by which the selected radiator's power exceeds the heat losses. Recommended reserve: 10–20%.
- Connection variant — the calculator displays connection designations: C (side), CV/VK (bottom right), CVL/VKL (bottom left), CVM/VKM (bottom center) with connection spacing.
Input data — what to enter and where to find it
Supply temperature [°C]
Design water temperature at the system supply. Value from the boiler or heat pump data sheet. Typical: 75–80 °C (old boiler), 55–70 °C (condensing boiler), 45–55 °C (heat pump). Lower supply temperature means a longer radiator for the same heat losses.
Return temperature [°C]
Design water temperature at the system return. The supply/return difference (Δt) depends on the heat source type: typically 15–20 K for boilers, 5–10 K for heat pumps. Smaller Δt means higher required flow rate and longer radiators.
Heat losses Q [W]
Room heating demand from calculations per PN-EN 12831 or a simplified estimate. For buildings after 2005 typically 50–70 W/m², for older buildings 80–120 W/m². Include losses through walls, windows, roof, and ventilation.
Radiator type (10, 11, 21, 22, 33)
The type defines the number of heating panels and convectors: Type 10 — 1 panel, no convector (thinnest, 47 mm). Type 11 — 1 panel + 1 convector (63 mm). Type 21 — 2 panels + 1 convector (66 mm). Type 22 — 2 panels + 2 convectors (102 mm, most popular). Type 33 — 3 panels + 3 convectors (157 mm, highest output).
Radiator height [mm]
Standard heights: 300, 400, 500, 600, 900 mm. Selection depends on the space below the window — maintain at least 100 mm from the sill and 100 mm from the floor. The most popular height is 600 mm. Lower radiators (300 mm) under low windows require greater length.
Key considerations for radiator selection
Place the radiator below the window — warm air from the convector interrupts the cold air stream falling along the glass. Radiator length should be 50–75% of the window width. With low-temperature parameters (heat pump 45/35 °C), the correction factor φ can be as low as 0.3–0.4, meaning radiators 2–3× longer than under nominal conditions. Don't forget a 10–20% power reserve.
Related heating system calculators
Radiator selection is one of the key steps in designing a central heating system. For a complete project, you may also find useful:
Want to learn more about radiator selection?
A guide explaining panel radiator types (10–33), connection designations (C, CV, CVL, CVM), converting power from nominal to actual conditions, nominal power tables, and a practical step-by-step sizing example:
How to select a radiator? Panel radiator sizing guide