Technical Standards and Safety Authority (TSSA) G3 Practice Exam

How does an orifice for a propane appliance compare in size to one for a natural gas appliance with the same input?

1. The same size as the natural gas orifice

2. Smaller than the natural gas orifice

3. Larger than the natural gas orifice

4. Interchangeable with the natural gas orifice

The correct answer is: Smaller than the natural gas orifice

In the context of appliances utilizing propane and natural gas, the size of the orifice is a critical factor due to the differences in the gas compositions and their respective energy content. Propane is denser and has a higher heating value than natural gas. As a result, to achieve the same energy output or input, the orifice size for a propane appliance must be smaller than that of a natural gas appliance. The smaller orifice for propane restricts the flow of gas, ensuring that the correct amount of gas is delivered to match its higher energy content. If a propane appliance were to use the same orifice size as a natural gas appliance, it would deliver too much gas, which could lead to incomplete combustion, producing carbon monoxide and reducing appliance efficiency. The smaller orifice ensures that the appliance operates safely and efficiently when using propane, conforming to the necessary standards for gas appliances. This fundamental understanding of gas characteristics and appliance design is critical for technicians and professionals working with these systems.