What is the main factor in determining the size of air supply openings for gas appliances?

The main factor in determining the size of air supply openings for gas appliances is indeed the BTU input of the appliance. This is because the BTU (British Thermal Unit) input measures how much energy the appliance consumes, and it directly correlates with the amount of oxygen needed for combustion. A higher BTU input means that the appliance will require a greater volume of air to ensure proper combustion occurs efficiently and safely. It is essential to provide sufficient air supply to ensure that the gas burns completely, which helps prevent the formation of harmful gases like carbon monoxide.

While the size of the appliance, type of gas used, and local code requirements can influence the overall installation and safety parameters, they do not solely dictate the air supply requirements. BTU input is a quantifiable measure that indicates the actual demand for combustion air, making it the primary factor in sizing air supply openings.