What is the minimum distance that the vent from a 75,000 BTUH category 3 furnace may terminate from a door?

The minimum distance that the vent from a 75,000 BTUH category 3 furnace may terminate from a door is indeed three feet. This distance is specified to ensure safety and functionality.

In the context of gas appliances, particularly those that utilize a venting system, it's critical to maintain clearances to prevent any potential hazards. A vent that is too close to a door can lead to exhaust gases entering the building when the door is opened, especially if there is any negative pressure created in the building. The three-foot requirement helps mitigate this risk by ensuring that the vent outlet allows for proper discharge of combustion gases away from openings where people may enter or exit.

This guideline focuses on safeguarding health and safety by preventing backdraft issues or the reintroduction of harmful gases into occupied spaces. Other options might represent lesser distances, which do not provide the same level of precaution, thereby not aligning with safety best practices established in building codes and guidelines for gas appliances.