About This Calculator: This calculator determines the minimum required effective area of natural ventilation openings for habitable spaces containing LPG open flame (unflued) appliances or open-flued appliances. The formula calculates the ventilation needed based on appliance ratings and the number of persons in the space. The minimum effective area should not be less than 4,000 mm².
Project Information
Ventilation Formula (Annex B)
A ≥ 2200 + 440U + 440F + 650P
Where:
Symbol
Description
A
Effective area in square millimetres (mm²)
U
Nominal input rating of unflued appliances in kilowatts (kW)
F
Nominal input rating of open-flued appliances in kilowatts (kW)
P
Number of persons for which the habitable space is designed
Input Parameters
Examples: cookers, stoves, ovens without flue
Examples: instantaneous water heaters with open flue
Maximum persons capacity shown on builder's plate
Ventilation Calculation Results
Example Calculations
Scenario
U (kW)
F (kW)
P (persons)
Result (mm²)
Small boat with stove only
3.0
0
2
4,820
Medium boat with stove and water heater
4.0
6.0
4
8,800
Large boat with full galley
6.0
10.0
8
14,240
Key Requirements from ISO 10239:2025 Annex B:
• Natural ventilation shall be provided into habitable spaces where appliances that are not room-sealed are installed
• Ventilation shall be supplied by at least two equally sized fixed openings in the habitable space
• One opening should be as high as practicable and one as low as practicable
• Both openings shall be positioned or shielded such that they cannot be inadvertently obstructed
• Natural ventilation pathways shall not pass through engine or machinery compartments other than through sealed ducting
• The minimum effective area shall take into account the reduction by screening or louvers
• When determining minimum sizing, consider any other air consuming appliances burning other types of carbon fuels
⚠ Important Note: The effective area calculated is the actual free air area. Account for reduction by screening or louvers when sizing actual openings. Typical reductions: wire mesh 60-70%, louvers 40-50%.