What is the approximate concentration of oxygen in air?

The concentration of oxygen in the atmosphere is approximately 21%. This percentage is based on the composition of dry air, which consists of about 78% nitrogen, 21% oxygen, and trace amounts of other gases, including argon, carbon dioxide, and others.

Understanding the correct concentration is important in HVACR applications, as the combustion efficiency of gas-burning appliances relies on the availability of oxygen. Insufficient oxygen can lead to incomplete combustion, resulting in harmful emissions and inefficient fuel use. Thus, knowing that oxygen concentration is around 21% provides a solid foundation for evaluating air quality and ensuring the safety and efficiency of heating systems and appliances.

The other options either underestimate or overestimate the typical percentage of oxygen in air, which could lead to misconceptions about air quality and combustion processes within HVACR systems.