To achieve "worst case" depressurization of the Combustion Appliance Zone, which of the following should be turned on?

To achieve "worst case" depressurization of the Combustion Appliance Zone (CAZ), it is essential to turn on all combustion appliances that are installed in that area. This includes the furnace, water heater, and stove, as each appliance contributes to the overall air movement and pressure dynamics within the zone. When all appliances are operating, they create a combined effect that enhances the depressurization effect. This is important during testing to evaluate how easily air can be drawn into the CAZ, which in turn affects the draft and safety of the appliances.

By activating all appliances, you can assess the system's response under the most demanding conditions, which is crucial for understanding how changes in air pressure influence the combustion process and appliance performance. This information is vital for ensuring adequate venting and preventing any potential back-drafting of harmful gases.

Individually operating each appliance might not create the same level of depressurization, as they do not replicate the interaction between multiple units functioning at once. Therefore, turning on all appliances provides a more accurate representation of the potential risks in the CAZ.