1|Page
HVAC UNIT 31 GAS HEAT
REVIEW QUESTIONS AND
CORRECT ANSWERS
The four types of gas furnace air flow patterns are _____, ______, _______ and
_______. - Correct-answer-Upflow, low-boy, downflow, and horizontal. pg 711-
712
Describe the function of a multipoise or multipositional furnace. - Correct-
answer-It can be installed in any position. It is very versatile. The configuration
can be changed very easy. pg 712
Describe the function of a draft safeguard switch. - Correct-answer-Also known as
a vent limit switch. They are NC switches usually mountd on the draft hood if the
furnace has one. They monitor the draft hood temperature and open when there
is any spillage of flue gas. pg 713
, 2|Page
Where are auxiliary limit switches used in heating applications? - Correct-answer-
They are used for counterflow and horizontal furnaces. They monitor room return
air temperature and interrupt burner operation when the temperature gets too
hot. pg 713
The specific gravity of natural gas is: ABCD - Correct-answer-D) .60 pg 714
What is a water and digital manometer? - Correct-answer-A water manometer is
used to measure gas pressure. It is a tube of glass or plastic formed into a U that is
half full of water. Gas pressure is determined by the difference in levels in the two
columns.
A digital manometer also measures gas pressure. It does not have any fluid to
spill. It can also measure both positive and negative pressures in inches of water
column. pg 715
The pressure at the manifold for natural gas is typically: ABCD - Correct-answer-D)
3.5 in WC pg 715
What is the approximate oxygen content of air? - Correct-answer-21% oxygen pg
716
HVAC UNIT 31 GAS HEAT
REVIEW QUESTIONS AND
CORRECT ANSWERS
The four types of gas furnace air flow patterns are _____, ______, _______ and
_______. - Correct-answer-Upflow, low-boy, downflow, and horizontal. pg 711-
712
Describe the function of a multipoise or multipositional furnace. - Correct-
answer-It can be installed in any position. It is very versatile. The configuration
can be changed very easy. pg 712
Describe the function of a draft safeguard switch. - Correct-answer-Also known as
a vent limit switch. They are NC switches usually mountd on the draft hood if the
furnace has one. They monitor the draft hood temperature and open when there
is any spillage of flue gas. pg 713
, 2|Page
Where are auxiliary limit switches used in heating applications? - Correct-answer-
They are used for counterflow and horizontal furnaces. They monitor room return
air temperature and interrupt burner operation when the temperature gets too
hot. pg 713
The specific gravity of natural gas is: ABCD - Correct-answer-D) .60 pg 714
What is a water and digital manometer? - Correct-answer-A water manometer is
used to measure gas pressure. It is a tube of glass or plastic formed into a U that is
half full of water. Gas pressure is determined by the difference in levels in the two
columns.
A digital manometer also measures gas pressure. It does not have any fluid to
spill. It can also measure both positive and negative pressures in inches of water
column. pg 715
The pressure at the manifold for natural gas is typically: ABCD - Correct-answer-D)
3.5 in WC pg 715
What is the approximate oxygen content of air? - Correct-answer-21% oxygen pg
716
