Gas water heaters must have combustion air access from which two points?

Gas water heaters require combustion air for efficient operation and safety. The correct answer is that they must have combustion air access from both the top and the floor. This design allows for necessary air circulation, which is essential for the combustion process.

When air enters from the top, it helps ensure that the heater can draw in fresh air as needed for burning the gas. Meanwhile, having access to air from the floor allows for cooler air to enter, which can be more dense and thus provides sufficient oxygen for proper combustion. This dual access is particularly important in enclosed spaces to prevent issues such as poor combustion, which can lead to dangerous carbon monoxide buildup.

In contrast, options that suggest other configurations—such as access from the floor only, a side wall, or solely side walls—do not adequately facilitate the needed airflow for the combustion process or could even create a hazardous condition. By requiring air from both the top and the floor, the system promotes a safe and effective combustion environment.