Which of the following statements is true about closed combustion systems in heating units?

Closed combustion systems are designed to enhance safety and efficiency by obtaining the air needed for combustion from the outside rather than from the occupied space. This allows these systems to operate without depleting indoor oxygen levels, which can be a concern in systems that draw air from within the home. By utilizing outside air, closed combustion systems also minimize the risk of backdrafting, where exhaust gases might enter the living space, which is a significant advantage in terms of indoor air quality and safety.

When air is sourced from the outside, it can also contribute to more stable combustion conditions, improving efficiency and performance. This is particularly important in tightly sealed homes where indoor air can be less stable. Furthermore, since the combustion process is isolated from the indoor environment, there is less potential for compromising indoor air quality, making closed combustion systems a favorable choice in modern heating design.