If an HVAC system's combustion air is calculated using a non-vented system, which method is acceptable?

In determining the appropriate method for calculating combustion air for an HVAC system that operates under a non-vented configuration, the use of outside air only is crucial for ensuring proper combustion. This is because outside air provides the necessary fresh oxygen needed for the combustion process while preventing the potential buildup of harmful gases or vapors that could occur if only room air or indoor air were used.

Non-vented systems rely on the assumption that adequate fresh air is supplied from the environment, which is essential to meet combustion efficiency and safety standards. Relying solely on the air inside the room can result in insufficient oxygen levels, leading to incomplete combustion, decreased efficiency, and the risk of carbon monoxide or other toxic gas accumulation. Thus, by using outside air, the system can maintain proper combustion ratios and safety.

This method aligns with guidelines and best practices in HVAC design, ensuring that the air quality and combustion efficiency are maintained at optimum levels. In contrast, using only room air or a combination of inside and outside air may not provide the adequate oxygen and ventilation required for safe operation.