When ascending into the atmosphere, atmospheric pressure decreases by 1 psi for every

• A. 2,500 feet
• B. 2,343 feet
• C. 3,343 feet
• D. 5,280 feet

Answer: (B)

As height increases, atmospheric pressure falls because the air becomes less dense. For quick, practical HVAC calculations, a common rule of thumb is that pressure drops by about 1 psi for roughly 2,343 feet of ascent. This provides a simple way to estimate how altitude affects ambient pressure without doing complex math. Starting from sea level pressure (about 14.7 psi), a drop of about 1 psi occurs after about 2,343 feet of climb, and further drops follow the same approximate rate. So the value that fits this widely used estimate is 2,343 feet. Remember, this is a helpful approximation; actual pressure changes with altitude are non-linear and depend on temperature and other factors.