Adequate ventilation is essential for personal health and safety and for the
correct and efficient operation of oxygen consuming appliances. Room-sealed
appliances have their own air supply built into the flue ductwork, but other
appliances take their combustion air supply directly from the cabin space.
Insufficient ventilation can lead to the production of carbon monoxide, which is
highly poisonous. The responsibility for the safety of the occupants on board
lies with the boat's owner and it's highly recommended that adequate fixed
ventilation is provided on boats where LPG or other fuel appliances are used.
The recommended amount of ventilation depends on the number and type of
appliances on board in accordance with the formula from British Standard
5482-3 i.e:

minimum effective area (mm2) = [2200xU]+[650xP]+[440xF]
Where:
U = total input rating (kW) for all appliances (including cookers)
without flues
F = input rating (kW) for all open or closed flue appliances
P = number of people for which the compartment is designed

The input rating for your appliances can normally be found on the
manufacturer's plate on the appliance and/or in the operating instructions.
The ventilation requirements then need to be split equally between:

• high level (ideally cabin roof) and
• as low as practicable.

Low level venting can be achieved by letting in cold air from vents in doors
and/or bulkheads, or by means of ducting from a higher level.

It's recommended that ventilators are fixed open on boats which are exclusively
used on inland waterways, however boats which go out to sea and are likely to
experience severe weather conditions may have ventilators that can be closed
for weathertightness. Where closable ventilators are used on your boat it's a
good idea to make use of a warning notice close to every appliance, e.g.
“Warning - open ventilator(s) before use”. [8.9]