Which category of vented appliance operates without positive vent static pressure and avoids excessive condensate production?

The correct answer is the category of vented appliance that operates without positive vent static pressure and avoids excessive condensate production is Category 1.

Category 1 appliances are designed to operate with a negative vent pressure, meaning they do not generate a positive pressure in the venting system. This is significant because negative pressure helps to ensure that no flue gases are pushed back into the living space, creating a safer environment. Also, because these appliances do not operate under positive pressure, they tend to produce less condensate. By avoiding excessive condensate, the risk of corrosion in the venting system is reduced, leading to improved maintenance and longevity of the appliance.

In contrast, the other categories function under different operating conditions. For example, Category 2 appliances also operate without positive static pressure but may not be designed with the same considerations regarding condensate. Categories 3 and 4 appliances typically involve either pressure relief systems or are designed to handle higher levels of condensate, which may not align with the specific characteristics described in the question. Thus, Category 1 perfectly fits the criteria specified.