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Gas Heating > 1 > Flashcards

1 Flashcards

0
Q

A good description of how a bi-metal fan switch operates the blower motor on a gas furnace is:

A

Temperature on - temperature off

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1
Q

A gas furnace is to be installed in a garage. The national standards require that the burners and ignition sources must be located ….. From the floor.

A

18 inches

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2
Q

Redundant gas valves used on gas furnaces will shut down if gas pressure exceeds?

A

13.5 in. W.C.

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3
Q

Burning one cubic foot of liquefied petroleum gas completely will produce approximately…. BTUs

A

2000-2500

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4
Q

LP gas has a specific gravity of:

A

1.5-2.0

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5
Q

What is the purpose of a spoiler screw located on a burner, or adjustable-shutters?

A

Mix primary air and gas

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6
Q

Furnace limit switches are wired in series with the:

A

Gas valve

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7
Q

A tech is using an extension ladder to work on a roof top unit. The top of ladder should extend how much beyond the support joint.

A

3 feet

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8
Q

A technician determines that a natural gas furnace has a defective heat exchanger. The technician should:

A

Inform the homeowner, turn the thermostat off, turn the gas to the furnace off.

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9
Q

A natural gas (standing pilot) furnace usually requires….gas pressure at the manifold and burners.

A

3.5 in. W.C.

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10
Q

The vent system for a condensing furnace is classified as…. by the national field gas code.

A

Category 4

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11
Q

Type B vent pipe must be kept at least….from combustible materials.

A

One inch

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12
Q

All condensing furnaces manufactured after 1992 must have a AFUE rating of at least:

A

90%

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13
Q

You have installed a category 4 two-type vent system that terminates through the roof of the residence. The elbow for the combustion air intake, above the roof, should:

A

Point down

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14
Q

The reason heating thermostats have anticipators is to?

A

Reduce overshoot

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15
Q

The typical flue gas temperature of a category 3 furnace is:

A

280F- 300F

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16
Q

The proper chemical name for natural gas is?

A

Methane

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17
Q

Burning one cubic foot of natural gas will produce approximately….BTUs.

A

900-1100

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18
Q

A furnace nameplate specifies a temperature rise of 40 to 70 degrees. Temperature measurements indicate a rise of 80 degrees. The most appropriate action is to:

A

Increase fan speed

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19
Q

A BTU is the amount of heat required to raise the temperature of one pound water:

A

One degree Fahrenheit

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20
Q

Natural gas piping must be sized to prevent excessive pressure drops. The national fuel gas code maximum pressure drop allowance is approximately:

A

.35 in. W.C.

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21
Q

Gas piping must be installed with a pitch of:

A

1/4” per 15’ run.

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22
Q

Pipe joint compound should be applied to:

A

Male threads less two end threads

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23
Q

A technician is installing a copper elbow on LP gas line; what type of solder is recommended:

A

95/5 solder

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24
Q

To burn one cubic foot of Natural Fas completely, at least…. of combustion air must be available.

A

15 cu ft.

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25
Q

The ignition temperature of Natural Has is?

A

1000-1200F

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26
Q

Air that is mixed with Natural Gas in the burner is called:

A

Primary air

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27
Q

A Natural Gas furnace is operating properly. How many cubic feet of flue gas are needed for every one cu. ft. burned?

A

20 cu. ft

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28
Q

The purpose of a flue baffle is:

A

Increase heat exchange.

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29
Q

The LP gas pressure supplied to the gas valve should be:

A

11-13 in. W.C.

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30
Q

An installed gas furnace should have a minimum of….inches for service access.

A

30 inches

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31
Q

What would cause the temperature limit safety to shut off the burner?

A

Fan motor failure

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32
Q

The cut off plate is a component of the:

A

Blower housing.

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33
Q

A “spud” or burner orfice does what?

A

Meters gas to the burner

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34
Q

A good thermocouple should read approximately …..on a D.C. meter.

A

18 millivolts

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35
Q

Liquefied petroleum, ( LP) gases are:

A

Propane and butane

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36
Q

Fan tine/temperature delay switches are used to:

A

Allow the vent to create proper draft and allow the heat exchanger to warm up

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37
Q

What instrument would a technician use to calculate return airflow to a furnace?

A

Meg get

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38
Q

A furnace with a hot surface igniter will not light. Before changing the igniter the technician should:

A

Check voltage to the igniter

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39
Q

A technician starts a standing pilot furnace and notices on main ignition the flames “roll out”. The technician suspects:

A

A faulty vent

40
Q

A technician servicing an LP gas furnace notices a tag stating it was converted from natural gas. He finds large amounts of soot in the heat exchanger. What could be the cause of this soot?

A

Orifice, (spud) too large.

41
Q

A customer tells a technician that his six mont old furnace stops heating before the residence is warm. This happens only on very cold nights. The technician lights the furnace, and tries to adjust the gas valve, but the flames do not change. He suspects:

A

A defective gas regulator.

42
Q

A standing pilot furnace had a bi-metal fan control. What are the factory settings?

A

Fan on 125F / Fan off 80F / Limit cut out 200F

43
Q

Type B vent pipe is constructed with an inner pipe and outer pipe. The inner pipe is made of what?

A

Aluminum

44
Q

On a dedicated vent system, a fire stop support is located:

A

Where it passes through a ceiling

45
Q

When venting Category 1 furnaces, it is sometimes necessary to increase the vent pipe size. The proper location to adapt to the larger vent is:

A

At the furnace connection

46
Q

You are installing 1/2” and 3/4” black iron pipe to a natural gas furnace. What is the approximate number of threads to cut?

A

8-10

47
Q

The proper name of the tool used to clean the inside of steel pipe is a?

A

Reamer

48
Q

Clevis, ring, and single hook are types of :

A

Hangers to support gas piping

49
Q

The proper name of the tool used to cut the threads of a steel pipe is a:

A

Die

50
Q

You are installing two sections of a rectangular sheet metal duct to the main supply line. What connectors are used to secure sections of the trunk line?

A

A connectors and drive clips.

51
Q

Metal ductwork tends to transmit noise and fan vibrations to conditioned spaces in residential installations. What type of connectors are specified to control this?

A

Flex connectors

52
Q

Duct wrap is used to insulate round metal ducts. What is the approximate R- value for “one inch” of this insulation?

A

R=4.0

53
Q

A category 1 natural gas furnace has a typical air temperature rise of:

A

40F-70F

54
Q

A technician connects the electrical circuit to an 80,000 BTU gas furnace with a 3-ton cooling system. The fan motor is rated 1/3 HP @ 120 VAC. What size conductor would normally be used? (Copper conductors)

A

12-14 AWG

55
Q

A GFCI circuit breaker detects:

A

Current leaks to ground

56
Q

A homeowner complained that his furnace makes a loud bang upon ignition. The technician decides to check the gas pressure and finds 3.2 in. W.C. at the manifold. The technician should:

A

Check the supply gas pressure

57
Q

The proper instrument for measuring carbon dioxide is a:

A

Combustion analyzer

58
Q

If voltage is applied across two speed terminals on a fan motor, the motor will:

A

Short out

59
Q

The maximum static pressure on a typical gas furnace blower system is:

A

.7 - .9 in. W.C.

60
Q

Induced draft furnaces have a vent safety switch that should open at?

A

100F

61
Q

Thermostat wire comes in two standard gauges:

A

22 and 20 AWG

62
Q

A technician solders a spade connector to a wire. What type of solder should he use?

A

Rosin core

63
Q

The anticipator is wired in series with the?

A

Gas valve

64
Q

To change the speed of a belt driven blower, the technician should:

A

Adjust motor pulley

65
Q

How much current does a typical flame sensor produce?

A

1-30 microamps

66
Q

A typical vent stack temperature on a category 1 furnace is?

A

350F-450F

67
Q

A customer complains that a 2 year old gas furnace will not light. The technician determines that the furnace locks out while attempting to light. He reads 19 VAC at the gas valve and concludes

A

The transformer could be faulty.

68
Q

The pilot assembly orifice of a spark ignition furnace is completely clogged. The technician should:

A

Replace it

69
Q

Carbon monoxide is dangerous. What percentage of CO is acceptable in a sample of the flue gas?

A

.04%

70
Q

A technician starts up a 15 year old natural gas furnace. The main burner lights and after 60 seconds the blower fan comes on, but the blower flames wave in one corner. The technician suspects:

A

A faulty heat exchanger

71
Q

A technician starts a spark type ignition furnace. The main burners light, but the spark igniter continues to spark. After 60 seconds, the blower fan comes on and the burner goes out. The technician suspects:

A

A faulty ignition board

72
Q

A gas furnace has an induced draft fan. What switch must operate properly before ignition sequence?

A

Differential air pressure

73
Q

A technician reads 0 Ohms between the common and low speed wires on a 120 VAC furnace motor. From this the technician determines that the winding is:

A

Shorted

74
Q

On his ohmmeter a technician reads infinity between the high and low speed wires on a 120 VAC furnace motor. What does this indicate?

A

Open

75
Q

The “bonnet capacity” of a furnace is:

A

Furnace input BTUs

76
Q

At what altitude does a gas furnace need to have adjustments made to operated properly?

A

2000 feet

77
Q

Failure to wire a replacement low voltage transformer in an electronic ignition furnace, based on it’s noted polarity, will:

A

Cause flame rectification problems

78
Q

A spark ignitor operates at?

A

10,000 VAC and higher

79
Q

What type of metallic conduit is recommended for indoor use only?

A

EMT

80
Q

A furnace nameplate specifies a temperature rise of 40 to 70 degrees. Temperature measurements indicate a rise of 80 degrees. The most appropriate action is to:

A

Increase fan speed.

81
Q

A dedicated vent system:

A

Is the only vent for an appliance.

82
Q

A yellow flame indicates:

A

Incomplete combustion is occurring. Soot may be created, which further hampers burner operation. Lack of primary air is the main cause.

83
Q

A lifting flame indicates:

A

The gas velocity is faster than the speed at which the gas can burn.

84
Q

Flashback indicates:

A

The gas is flowing slower than the speed at which burn is occurring.

85
Q

A floating flame indicates:

A

Incomplete combustion is occurring. Soot may be created, which further hampers burner operation. Lack of primary air is the main cause.

86
Q

Fan speed should be set by:

A

The temperature rise called for on the data plate.

87
Q

Gas flow to a natural gas furnace can be checked:

A

Using the gas meter installed at the site

88
Q

It the exact amount of air is supplied and perfect combustion occurs, in a natural gas furnace, a specific percentage of CO2 content will be present in the flue gases. What percentage will be present?

A

11.7% to 12.2%

89
Q

When an LP unit is properly installed and operating normally, the CO2 content of the exhaust gases:

A

11% to 12%

90
Q

While evaluating a gas valve that failed to open, the technician determined that; the gas valve knob in the proper position - the thermostat was calling for heat - the valve is an electric ignition type- continuity of the main gas valve coil was good - and proper voltage was present at the main gas valve coil terminal(s). What action should be taken?

A

Replace the gas valve

91
Q

In a house with central return system and seven supplies located in rooms with interior doors, what outcomes are likely when the interior doors ate closed and the air handler is turned on?

A

The static pressure that the HVAC fan gas to run against is increased resulting in less air through the air handler. The main body of the house experiences negative pressure. The rooms behind the closed interior door become positively pressurized.

92
Q

The formula (x=sensible heat btu/h/ 1.08 xTD) is used to calculate what?

A

CFM

93
Q

The most common burner used in induced draft furnaces is:

A

inshot

94
Q

A technician wraps a thermostat wire ten times around his clamp-on ammeter and measures 5.5 amps between R and W terminals on the thermostat sub-base. He should set the heat anticipator to:

A

.50

95
Q

A gas valve with 100% shut-mean:

A

gas to the pilot burner is shut-off

96
Q

A gas furnace has an electronic control board. How is the fan cycled during heating?

A

Time

97
Q

A primary cause of burner “flashback” is:

A

low manifold pressure

98
Q

A technician needs to run thermostat wire 75 feet. To avoid a voltage drop the technician should use:

A

20 AWG

Gas Heating (1 decks)

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