Which opening is often disregarded in calculating air supply for enclosed appliance installations?

In the context of calculating air supply for enclosed appliance installations, the side opening is often disregarded. This is because, when determining the adequate volume of combustion air required for the proper functioning of fuel-burning appliances, the primary focus tends to be on openings that allow for effective airflow directly related to the appliance's operation—such as lower and upper openings.

Lower openings are crucial as they facilitate the intake of air needed for combustion from the lower levels of a space, while upper openings can serve to allow for the escape of exhaust gases or to balance the air supply. The through-wall openings are significant as they provide a direct pathway for outside air, which is important for ensuring a sufficient and uncontaminated air supply.

In contrast, side openings may not contribute effectively to the overall airflow required for combustion since they are typically positioned away from the primary flow paths of air entering or leaving the space. As a result, they do not play a major role in the calculations for air supply, which is focused on ensuring a sufficient and proper exchange of air for safe and efficient appliance operation.