HVAC Gas Heat Exam (Latest 2024/ 2025 Update) 100% Correct Questions and Verified Answers| Grade A

HVAC Gas Heat Exam (Latest 2024/ 2025 Update) 100% Correct Questions and Verified Answers| Grade A Q: Why is specific gravity of a gas important? Answer: It affects the gas flow through the piping and through the orifice of the furnace. Q: What is an orifice and a spud? Answer: An orifice is a precisely sized hole in a gas fitting which gas flows from the manifold to the burners. A spud is another name for a gas fitting. Q: If both a light gas and a heavy gas are at the same pressure, which will flow more through a given orifice? Answer: A light gas will flow more through an orifice. Q: How many inches WC is in 1 psig? Answer: 27.7 " WC Q: Why is manifold pressures expressed in inches WC instead of psig? Answer: Manifold pressures are very small, less than 1 psig. Inches WC is a much more precise measurement for less than 1 psig. Q: How is inches WC calculated with a water manometer? Answer: A tube is formed into a U and filled halfway with water. Gas pressure is piped to one side of the tube and the difference in their heights is inches WC. Q: What are the manifold pressures for natural gas and LP gas? Answer: Natural gas 3 to 3.5 in. WC LP gas 9 to 11 in. WC Q: T or F: both a water and digital manometer can measure positive and negative pressures. Answer: False- only a digital manometer can measure negative pressure. A water manometer can only measure a positive pressure. Q: What are the three elements for combustion? Answer: Fuel Oxygen Heat Q: If one of the elements are not available, can there still be combustion? Answer: No, if any of the elements are missing, no combustion is possible. Q: How much oxygen is in the air we breathe? Answer: The air contains 21% oxygen. Q: When there is perfect combustion, what elements result from the combustion? Answer: Carbon dioxide (CO2), water vapor (H2O) and heat. Q: If there is poor combustion, what is the dangerous by-product that always results? Answer: Carbon monoxide (CO). Q: Why is soot bad for a furnace? Answer: It can collect on the heat exchanger and acts like an insulator. This reduces efficiency of the furnace. Q: What is the fancy name for the reduction in burner diameter in the burner tube? Answer: A venturi.