ESCO Air Conditioning Practice Exam 2025 - Free AC Certification Practice Questions and Study Guide

In a vacuum of 28 inHg, the atmospheric pressure is significantly reduced compared to standard atmospheric pressure (14.7 psi or 29.92 inHg). At this lower pressure, water's boiling point decreases.

Under normal atmospheric conditions, water generally boils at 212°F. However, as pressure decreases, the temperature at which water will turn to vapor also decreases. In a vacuum, water can boil at much lower temperatures due to the decreased pressure acting on the liquid water.

At a vacuum of 28 inHg, water vaporizes at approximately 10°F. This is because the lower pressure reduces the energy required for water molecules to escape into the gaseous phase, allowing for vaporization to occur at this much lower temperature compared to what would be expected under normal conditions.

Understanding this concept is crucial not only for questions like this but also for practical applications in refrigeration and air conditioning, where pressure fluctuations and boiling points play significant roles.