Forced-Air Heating Systems

Question 1

What are the two common materials electric heating elements are made from?

Answer 1

Tungsten and Nichrome

Question 2

What is the primary function of the indoor fan motor in an electric furnace?

Answer 2

To move air from the return air ducts to the space being warmed.

Question 3

What device does not provide 100% gas shutoff in a gas fired furnace?

Answer 3

Pilot Safety Switch

Question 4

What efficiency rating classifies a furnace as mid-efficient?

Answer 4

80-83%

Question 5

Where would the sensing portion of a secondary high limit device be placed?

Answer 5

Blower Compartment

Question 6

What is the purpose of a heat recovery ventilator?(HRV)

Answer 6

To recover heat from an exhaust fan.

Question 7

What is the most likely faulty component if a high efficient furnace is not running correctly and the error code indicates a flame proving failure?

Answer 7

Gas Valve

Question 8

What is the preferred range for the fan on setting of the combination fan controller?

Answer 8

49-60C

Question 9

What device is used to ignite the main burner in efficient gas fired furnaces?

Answer 9

Hot surface ignitor.

Question 10

What safety feature ensures gas is not released if the flame is not detected?

Answer 10

FLAME SENSOR

Question 11

What efficiency do mid to high efficiency units operate at?

Answer 11

90%-96%

Question 12

What are the components of an electric heating unit?

Answer 12

Heating element, thermostat, reflector, fan

Question 13

Describe a Reflector in an electric heating unit

Answer 13

Located behind the heating element to direct radiant heat forward

Usually made of polished aluminum or another highly reflective material.

Question 14

What is the purpose of the indoor fan motor?

Answer 14

To move air from the return airducts across the heat exchanger and through the space being warmed.

Question 15

Where is a 120v heating system commonly used?

Answer 15

Commercial and industrial applications.

(Warehouses, workshops, garages, larger buildings where temp differential is not as important as in residential application.)

Question 16

Why does a 120v heating system thermostat have no anticipator?

Answer 16

Temperature differential is not as important as in a personal residence.

Question 17

What are the Fan-ON and fan-OFF settings?

Answer 17

ON - 49-60C

OFF- 32-38

Question 18

How do step open gas valves work?

Answer 18

Step open gas valves open in two stages to reduce the initial rush of gas into the burner, thus reducing the size and intensity of the ignition explosion in the heat exchanger.

Question 19

What is the purpose of flame proving systems?

Answer 19

To shut off the flow of fuel through the gas valve if the pilot flame goes out.

(thermocouples are used to prove the existence of a pilot flame)

Question 20

What are the two reasons for pressing the manual reset when starting a gas fired furnace?

Answer 20

1) To allow pilot gas to pass through the valve to the pilot burner

2) To hold the armature up into the power unit.

Question 21

What is the most common type of valve used in modern heating units?

Answer 21

Combination Gas Valve

Question 22

Why were pilot safety switch dangerous?

Answer 22

It would not prevent gas from flowing into the extinguished pilot burner.

Question 23

What are other names for a safety gas valve?

Answer 23

100% shutoff valves, safety gas valves, automatic pilot valves

Question 24

Solenoid Valves control the flow of gas directly by:

Answer 24

By mean of an electrically operated plunger.

Question 25

The Solenoid Valve is a fast acting primary control device. True or False

Answer 25

True

Question 26

What does a diaphragm valve do?

Answer 26

Turns the supply of gas to the main burner on or off. Typically smaller than the solenoid types Gas pressure operates the valve

Question 27

Which is faster to respond to a change in control circuit status? Diaphragm Valve or Solenoid Valve

Answer 27

Solenoid Valve (Takes time to bleed gas from the diaphragm)

Question 28

What is incorporated in a combination gas valve?

Answer 28

The gas regulator Safety gas valve Power unit Main gas valve Manual gas shutoff

Question 29

What is the preferred valve for both natural gas and propane fired systems?

Answer 29

Combination Gas Valve

Question 30

What are the two types of fans?

Answer 30

Belt driven type Directly Coupled drive

Question 31

The fractional horsepower motors typically range from:

Answer 31

1/4hp to 3/4 hp

Question 32

What are the components of a 24v system?

Answer 32

Thermostat Gas Valve Transformer Secondary

Question 33

What are the components of the 120v circuit?

Answer 33

Fan control switch and transformer primary

Question 34

Where is the high limit connected 24v or 120v circuit?

Answer 34

The high limit may be connected into either the 24v or 120v circuits

Question 35

When does the HL/Fan control switch reset?

Answer 35

When it drops 11C below the setpoint

Question 36

What are the benefits of two stage heating?

Answer 36

Higher efficiency and better temperature control

Question 37

How can fan cycling be prevented?

Answer 37

By maintaining proper settings and by keeping at least 17C to 22C differential between the settings.

Question 38

What is the efficiency of condensing gas furnaces?

Answer 38

90% - 98%

Question 39

In a high efficient gas furnace, PVC exhaust piping can be routed vertically or horizontally as it exits the structure. True or False?

Answer 39

True

Question 40

What are the major components of an efficient gas fired forced air furnace?

Answer 40

Combustion Air components Burner assembly Fan blower assembly Electronic printed circuit control board (ECB)

Question 41

What is the minimum AFUE for new furnaces?

Answer 41

78% AFUE

Question 42

What are the 4 main combustion air components?

Answer 42

Combustion Air Blower (flue gas vent blower/system purge blower) Combustion Air Prove Switch Heat Exchanger Primary high limit safety switch

Question 43

What does the heat exchanger do?

Answer 43

Transfers heat from the combustion chamber to the circulating air and separates the products of combustion from the circulating air.

Question 44

How can the effectiveness of the heat exchanger be improved?

Answer 44

By increasing the heat exchanger surface area by using thinner metals that transfer the heat more effectively to the circulating air.

Question 45

What are high limit safety controls?

Answer 45

Safety controls that prevent mid-efficient furnace burners from operating during a dangerously high temperature event.

Question 46

What is the set point for high limit safety controls?

Answer 46

Between 82-94C

Question 47

The DSI control board provides the spark electrode with a high voltage potential of up to ________V

Answer 47

Up to 5000V

Question 48

What are Hot Surface Ignitors made from?

Answer 48

Silicon Carbide or Silicon Nitride

Question 49

Under certain conditions when a flame is present between two points of electrical potential difference, current flows through the flame. This is called:

Answer 49

Flame Rectification

Question 50

Roll Out Limit control prevents the furnace from firing while:

Answer 50

a flame roll out condition exists. (flame and flue gasses exit the combustion chamber by a path other than the flue)

Question 51

Source Voltage over a control device indicates:

Answer 51

An open switch

Question 52

Source Voltage over a load device will indicate:

Answer 52

That all control devices ahead of it are closed

Question 53

What are the 5 steps for troubleshooting a Forced-Air Heating System?

Answer 53

1.) Observe the cycle of operation. 2.)Measure Voltages 3.)Confirm Fault. 4.) Fix the fault. 5.) Confirm Operation

Question 54

The high limit control is usually located in the:

Answer 54

Heat Exchanger