Which of the following is a requirement for installing gas water heaters?

The requirement that gas water heaters need proper ventilation is crucial for ensuring safety and efficiency in their operation. Gas water heaters produce combustion gases, including carbon monoxide, which can be hazardous if not properly vented outside the living space. Adequate ventilation helps to remove these gases from the area where the water heater is installed, reducing the risk of poisoning or fire hazards.

Proper ventilation systems can include exhaust pipes and flues that are designed to channel harmful gases away from the home and ensure that fresh air is supplied for combustion. This ventilation is not just a recommendation; it is mandated by various building codes and standards because it plays a critical role in operating a gas water heater safely.

In contrast, the other options do not constitute universal requirements for the installation of gas water heaters. For instance, while a dedicated power source may be necessary for certain models that require electrical components, not all gas water heaters need one. Installing a water heater in living spaces is generally discouraged due to safety concerns, and direct exterior access is not a standard requirement. Thus, the need for proper ventilation stands out as a fundamental requirement when installing gas water heaters.