Which of the following statements is true regarding gas appliance installations?

The statement regarding gas appliance installations that is true is that combustion air must be provided in enclosed garages with appliances. This is essential for ensuring that gas appliances have a sufficient supply of air for proper combustion. In enclosed spaces like garages, the potential for insufficient air can lead to incomplete combustion, which may produce dangerous carbon monoxide or result in inefficient operation of the appliance. Therefore, proper ventilation or combustion air supply is critical for safety and efficiency.

The other statements present scenarios that are not compliant with standard practices or codes. For instance, the requirement regarding the distance from windows is not standardized in the same way as the necessity for combustion air, and while particular standards may exist, they tend to be more specific than simply stating a uniform measurement like 5 feet. Installing gas appliances on roofs is not common practice due to safety and accessibility concerns. Lastly, the assertion that only electric appliances can be used in enclosed spaces is incorrect; many gas appliances can also be safely used in enclosed areas provided proper ventilation and clearance guidelines are followed.