A technician using a manometer on an induced draft furnace is most likely testing for what?

Using a manometer on an induced draft furnace is primarily focused on measuring negative pressure within the flue or draft system. Induced draft furnaces use a fan to pull air through the combustion chamber and into the flue, creating a negative pressure environment that promotes efficient venting of combustion gases.

By employing a manometer, the technician can determine if the negative pressure is within the required operational range for safe and effective furnace performance. Proper negative pressure levels are crucial for ensuring that exhaust gases are adequately vented outside and that there's a sufficient air supply for combustion within the furnace. If the negative pressure is too low, it could lead to inadequate venting, which may pose safety risks, such as carbon monoxide backing up into the living space.

The other options are related but do not directly pertain to the primary function of an induced draft furnace as they focus on different aspects of furnace operation.