What is measured during a draft test in combustion appliances?

During a draft test in combustion appliances, the primary focus is on the draft pressure in the vent pipe. This measurement is crucial because it indicates how effectively the combustion gases are being expelled from the appliance and the overall venting system's ability to maintain a proper airflow. A positive draft is necessary to ensure that harmful gases do not leak back into the living space and that the appliance operates efficiently.

Understanding the draft pressure helps in diagnosing potential issues such as blockages in the venting system, improper installation, or inadequate combustion air supply, which can all lead to unsafe operating conditions. This assessment is critical for safety in combustion appliances, as proper draft is essential to prevent the buildup of dangerous gases such as carbon monoxide.

The other options pertain to different aspects of the combustion appliance or its operation but do not specifically evaluate the critical effectiveness of gas venting as draft pressure does.