HVAC Unit 31 Gas Heat Exam
Study Guide: GRADED A+.
Practice Questions and Verified
Answers. Latest 2026 Update
Name the four main components of a gas fired heating system. - Ans✔✔-
Manifold and controls
Burners
Heat exchanger
Venting system
Name the four types of furnace flow patterns. - Ans✔✔-Upflow
Low-boy
Downflow
Horizontal
Which type of furnace is usually found in basements that have low headroom?
- Ans✔✔-Low-boy
What is another name for a downflow furnace? - Ans✔✔-Counterflow
,Where do you usually find horizontal furnaces? - Ans✔✔-In crawl spaces, attics
and suspended from floor joists in basements.
What is so special about multipoise furnaces? - Ans✔✔-They can be installed in
any position. They are very versatile and give installers the option of upflow,
downflow, horizontal right or horizontal left discharge.
Why do multipoise furnaces have extra safety controls? - Ans✔✔-Because
these furnaces can be placed in four different configurations, they must
multiple safety controls designed into the furnace.
Where are flame rollout switches usually installed? - Ans✔✔-They are installed
near the top of the burner box, where the flame is most likely to roll out.
How do auxiliary limit switches work? - Ans✔✔-They are used for counterflow
and horizontal furnaces. They are usually bimetallic and are mounted on the
warm air blower housing to they can monitor room return air temperature and
interrupt the burners when the temperature gets too hot.
Are vent limit / draft safeguard switches NC or NO and what do they do? -
Ans✔✔-They are NC switches and monitor the draft hood temperature and
open when there is any spillage of flue gas.
What are the three commonly used gas fuels? - Ans✔✔-Natural gas
Manufactured gas
Liquified petroleum or LP gas
, What is the specific gravity of natural gas and is it lighter than air? - Ans✔✔-
The specific gravity is .60 and it is lighter than air so it rises.
How many Btu of heat energy do you get from 1 cubic foot of natural gas? -
Ans✔✔-1050 Btu of heat energy.
T or F: Natural gas is poisonous to breath and has a distinctive smell. - Ans✔✔-
False. It is not poisonous and has no odor. In fact, an odorant is added to it to
make leak detection easier.
What gases is liquified petroleum made of? - Ans✔✔-It can be liquified
propane, butane or a combination of both.
Why is butane not a popular fuel source? - Ans✔✔-It has a high boiling point of
31° and is difficult to keep the pressure high enough to move the gas to the
main burner.
How many Btu of heat energy do you get from 1 cubic foot of propane ? -
Ans✔✔-2500 Btu of heat energy.
What is the specific gravity of propane? - Ans✔✔-1.52 which means it is
heavier than air and will sink if released to the air.
How many Btu of heat energy do you get from 1 cubic foot of butane? -
Ans✔✔-3200 Btu of heat energy.
Why is specific gravity of a gas important? - Ans✔✔-It affects the gas flow
through the piping and through the orifice of the furnace.
Study Guide: GRADED A+.
Practice Questions and Verified
Answers. Latest 2026 Update
Name the four main components of a gas fired heating system. - Ans✔✔-
Manifold and controls
Burners
Heat exchanger
Venting system
Name the four types of furnace flow patterns. - Ans✔✔-Upflow
Low-boy
Downflow
Horizontal
Which type of furnace is usually found in basements that have low headroom?
- Ans✔✔-Low-boy
What is another name for a downflow furnace? - Ans✔✔-Counterflow
,Where do you usually find horizontal furnaces? - Ans✔✔-In crawl spaces, attics
and suspended from floor joists in basements.
What is so special about multipoise furnaces? - Ans✔✔-They can be installed in
any position. They are very versatile and give installers the option of upflow,
downflow, horizontal right or horizontal left discharge.
Why do multipoise furnaces have extra safety controls? - Ans✔✔-Because
these furnaces can be placed in four different configurations, they must
multiple safety controls designed into the furnace.
Where are flame rollout switches usually installed? - Ans✔✔-They are installed
near the top of the burner box, where the flame is most likely to roll out.
How do auxiliary limit switches work? - Ans✔✔-They are used for counterflow
and horizontal furnaces. They are usually bimetallic and are mounted on the
warm air blower housing to they can monitor room return air temperature and
interrupt the burners when the temperature gets too hot.
Are vent limit / draft safeguard switches NC or NO and what do they do? -
Ans✔✔-They are NC switches and monitor the draft hood temperature and
open when there is any spillage of flue gas.
What are the three commonly used gas fuels? - Ans✔✔-Natural gas
Manufactured gas
Liquified petroleum or LP gas
, What is the specific gravity of natural gas and is it lighter than air? - Ans✔✔-
The specific gravity is .60 and it is lighter than air so it rises.
How many Btu of heat energy do you get from 1 cubic foot of natural gas? -
Ans✔✔-1050 Btu of heat energy.
T or F: Natural gas is poisonous to breath and has a distinctive smell. - Ans✔✔-
False. It is not poisonous and has no odor. In fact, an odorant is added to it to
make leak detection easier.
What gases is liquified petroleum made of? - Ans✔✔-It can be liquified
propane, butane or a combination of both.
Why is butane not a popular fuel source? - Ans✔✔-It has a high boiling point of
31° and is difficult to keep the pressure high enough to move the gas to the
main burner.
How many Btu of heat energy do you get from 1 cubic foot of propane ? -
Ans✔✔-2500 Btu of heat energy.
What is the specific gravity of propane? - Ans✔✔-1.52 which means it is
heavier than air and will sink if released to the air.
How many Btu of heat energy do you get from 1 cubic foot of butane? -
Ans✔✔-3200 Btu of heat energy.
Why is specific gravity of a gas important? - Ans✔✔-It affects the gas flow
through the piping and through the orifice of the furnace.
