UNIT 53 REVIEW QUESTIONS ANSWER KEY GO BACK TO INDEX
53-1) List the safety precautions that should be observed when starting a gas furnace.
Don’t turn anything on until you have inspected the furnace!
53-2) Explain the difference between natural gas and propane.
53-3) What is the most common manifold pressure for natural gas furnaces?
53-4) What is the most common manifold pressure for propane furnaces?
53-5) A technician is clocking the gas usage of a gas furnace. It takes 30 seconds for
the 1/2 foot dial to make 1 revolution. What is the rate of gas flow in cubic feet
per hour?
53-6) Use the gas flow rate calculated from question 5 to determine the input in
53-7) What is the correct vent size for a 50,000 BTU/hr input induced draft furnace
with a 15 foot lateral run and a 30 foot vent height?
53-8) What is the smallest fan assisted furnace that can be connected to an existing 6
inch type B vent that is 30 feet high with a lateral run of 15 feet?
53-9) What size should the combustion air openings be for a room with an 80,000
BTU/hr input furnace and a 35,000 BTU/hr water heater if the openings are
opening directly into a ventilated attic and a ventilated crawlspace?
53-10) What size should the openings be in question 9 if the air is traveling through
horizontal ducts to the outside?
53-11) Where do you measure the temperature when checking furnace temperature
rise?
53-12) What is the temperature rise of a furnace with a supply air temperature of
130°F and a return air temperature of 75°F?
53-13) How can the temperature rise of a furnace be reduced if the temperature rise is
too high?
53-14) What are the normal oxygen and carbon dioxide percentages in the flue gas in
a properly operating gas furnace?
53-15) How is net stack temperature determined?
53-16) What is the lowest temperature butane can be used as a heating fuel?
53-17) What is the difference between vent sizing for natural draft appliances and fan
assisted appliances?
53-18) Why are most furnaces manufactured today either Category I or Category IV
furnaces?
53-19) What is the difference between a vent connector and the vent?
53-20) How is the correct manifold pressure for any particular installation
determined?