What tool is commonly used to measure gas pressure?

A manometer is the appropriate tool for measuring gas pressure because it is specifically designed to measure the pressure of gases in various applications, such as HVAC systems. It operates on the principle of balancing the weight of a column of liquid against the pressure of the gas being measured. This allows for precise measurement of pressure differences and is crucial for diagnosing issues in gas appliances or systems, ensuring they operate safely and efficiently.

Other tools listed do not serve this purpose. A thermometer measures temperature, while a multimeter is primarily used for evaluating electrical parameters such as voltage, current, and resistance. A barometer measures atmospheric pressure but is not suitable for measuring the pressure of gas in HVAC systems. Thus, the manometer is the best choice for this specific task.