Gas Room Ventilation Calculator

A room with gas-fired appliances needs enough air for safe combustion and enough ventilation to remove heat and any leaked gas. This calculator estimates the combustion air and the high/low ventilation openings for a boiler or gas appliance room from the appliance input, its efficiency and the room volume, so you can size the fresh-air louvres and confirm the room is adequately ventilated to NFPA 54 / ASHRAE practice.

Combustion air must never be starved, incomplete combustion produces carbon monoxide. Codes give combustion-air openings per unit of input and require both high and low openings for natural ventilation, or a mechanical supply interlocked with the burners. Free area (not gross) governs, so louvre and mesh factors apply. Always follow the appliance installation manual and the adopted gas code; boiler rooms often also need heat-removal ventilation beyond the combustion minimum.

A room with a 200 kW gas boiler at 90% efficiency rejects about 20 kW of casing and flue heat. The calculator sizes combustion air to the 200 kW input plus ventilation air to remove that heat, then converts to high- and low-level free louvre areas and checks the resulting air-change rate against the room volume.

Combustion air first

The primary requirement is enough air for complete combustion of the total appliance input. This is a safety item. Never trade it away for architectural reasons, and never share it with extract systems that could depressurise the room.

Heat removal

Boiler and plant rooms also collect casing and flue heat, so ventilation is sized to keep the room within a temperature limit, often exceeding the bare combustion minimum, especially in hot climates.

Openings and interlocks

Natural ventilation uses free-area high and low openings; mechanical ventilation must be interlocked with the burners. Follow the appliance manual and gas code and confirm carbon monoxide detection where required.