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Safety Valve Selection
Safety valve sizing calculator per PN-B-02414
Professional calculator for sizing safety valves in closed heating systems. Calculations are performed according to PN-B-02414:1999 for water boilers and district heating substations with heat exchangers. The calculator determines the required valve capacity, minimum flow channel area, and seat diameter — ready data for ordering from the manufacturer.
A tool for HVAC designers, technical inspection officers, and installers selecting boiler room safety devices. Results can be exported as an A4 PDF, ready for project documentation or submission to technical inspection authorities.
How to use the calculator in 3 steps
Select calculation mode: "Water Boiler" — when installing or replacing a heating boiler, or "Heat Node" — when protecting the system downstream of a heat exchanger connected to the district heating network.
Enter data: for boiler — thermal power Q [kW] and valve set pressure [bar]; for heat node — set pressure, system volume V [m³], and network nominal pressure p₂ [bar]. Select valve type or enter a custom discharge coefficient α from the manufacturer's catalog.
Read the result: the calculator will show the required valve capacity, minimum channel area A [mm²], and diameter d₀ [mm]. Compare with available valve seat diameters and select the smallest valve meeting the requirements.
What the safety valve calculator computes
The program determines all parameters needed for proper safety valve selection per PN-B-02414:
- m — required safety valve capacity [kg/h] — the amount of steam (boilers) or water (heat nodes) that the valve must be able to discharge.
- A — minimum valve flow channel area [mm²], calculated from capacity and discharge coefficient α.
- d₀ — minimum valve seat channel diameter [mm], derived from area A.
- DN — proposed valve connection size — the smallest standard size whose channel diameter d ≥ d₀.
- Calculation variant (heat nodes only) — the program automatically identifies variant a) or b) per PN-B-02414 based on the pressure ratio p₂ and p₁.
Input data — what to enter and where to find it
Calculation mode
"Water Boiler" — steam capacity calculations per PN-81/M-35630 (valve must discharge steam generated by the boiler during failure). "Heat Node" — liquid capacity calculations per PN-B-02414 section 2.2.2.2 (valve protects against pressure exceedance due to uncontrolled inflow from the network).
Thermal power Q [kW]
Nominal thermal power of the boiler (boiler mode). Using the formula m = Q × 3600 / r, the calculator determines the steam flow the valve must discharge. Use the power from the boiler nameplate, not the building's design heat demand.
Valve set pressure [bar]
Safety valve opening pressure. For domestic systems usually 3 bar, for industrial boiler rooms 6 bar. Must be less than or equal to the maximum allowable pressure of the weakest system component (boiler, heat exchanger, expansion vessel).
Discharge coefficient α
Value from the valve manufacturer's catalog. Typical values: diaphragm valves ~0.50, low-lift ~0.30, full-lift ~0.70. Higher α means a smaller required valve size for the same capacity.
System volume V [m³] (heat node mode)
Total water volume in the system downstream of the heat exchanger — pipes, radiators, buffer tank. For heat nodes with variant a) (p₂ ≤ p₁), valve capacity depends linearly on volume: M = 0.44 × V [kg/s].
Key considerations for valve selection
The safety valve must be sized strictly per the standard — never use a valve with a diameter smaller than calculated. For heat nodes, the minimum connection diameter is 15 mm (PN-B-02414 section 2.2.2.2). No isolation valve may be installed between the boiler and the safety valve. Route the discharge pipe above the floor or to a funnel with a trap — never directly to the drainage system. After installation, verify the opening pressure with a test gauge.
Related boiler room design calculators
The safety valve is one of the key safety components in a heating system. For complete boiler room design, you may also find useful:
Want to learn the theory and formula derivation?
A comprehensive guide with the calculation algorithm per PN-B-02414 and PN-81/M-35630, a sizing example for a 50 kW boiler, variants a) and b) for heat nodes, SYR diaphragm valve specifications, and common mistakes:
Safety valve sizing — standards, calculations, practice