HVAC UNIT 31 GAS HEAT REVIEW
QUESTIONS WITH 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
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
The typical manifold pressure for propane gas is _____ in WC. - CORRECT ANSWER-
11 in WC pg 715
Why is excess air supplied to all gas-burning appliance burners? - CORRECT
ANSWER- To make sure that all of the methane is burned. pg 717
The purpose of the gas regulator at a gas burning appliance is to: ABCD - CORRECT
ANSWER- B) decrease the pressure to the burner. pg 718
T or F: All gas valves snap open and closed. - CORRECT ANSWER- False - the valves
are solenoid, diaphragm and heat motor. pg 719
Which of the following features does an automatic combination gas valve have? ABCD -
CORRECT ANSWER- D) all of the above. It has a pressure regulator, pilot safety
shutoff, and redundant shutoff feature. pg 721
What is the function of the servo pressure regulator in a modern combination gas valve?
- CORRECT ANSWER- It monitors the outlet pressure of the gas valve. Any gas outlet
pressure change is instantly sensed and reflected back to the diaphragm. The regulator
then repositions the diaphragm and disc to change the flow rate through the servo
pressure regulator valve.
It is a self-balancing system that works off gas valve outlet or working pressure and is
independent of flow rate. pg 723
QUESTIONS WITH 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
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
The typical manifold pressure for propane gas is _____ in WC. - CORRECT ANSWER-
11 in WC pg 715
Why is excess air supplied to all gas-burning appliance burners? - CORRECT
ANSWER- To make sure that all of the methane is burned. pg 717
The purpose of the gas regulator at a gas burning appliance is to: ABCD - CORRECT
ANSWER- B) decrease the pressure to the burner. pg 718
T or F: All gas valves snap open and closed. - CORRECT ANSWER- False - the valves
are solenoid, diaphragm and heat motor. pg 719
Which of the following features does an automatic combination gas valve have? ABCD -
CORRECT ANSWER- D) all of the above. It has a pressure regulator, pilot safety
shutoff, and redundant shutoff feature. pg 721
What is the function of the servo pressure regulator in a modern combination gas valve?
- CORRECT ANSWER- It monitors the outlet pressure of the gas valve. Any gas outlet
pressure change is instantly sensed and reflected back to the diaphragm. The regulator
then repositions the diaphragm and disc to change the flow rate through the servo
pressure regulator valve.
It is a self-balancing system that works off gas valve outlet or working pressure and is
independent of flow rate. pg 723
