NATE Gas Heating Exam

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Since 1992, the United States Department of Energy has required that all furnaces sold and installed from that date on must have an AFUE of no less than:

A: 70%

B: 75%

C: 78%

D: 80%

C: 78%

Many pre-1992 furnaces have efficiencies around _______.

A: 10%

B: 40%

C: 60%

D: 80%

C: 60%

Today, furnaces with AFUE ratings greater than _____ are available.

A: 85%

B: 90%

C: 100%

D: 110%

B: 90%

A thermocouple is used with:

A: Intermittent pilot systems

B: Direct spark ignition systems

C: Glow coil ignition systems

D: Standing pilot ignition systems

D: Standing pilot ignition systems

The purpose of the gas pressure regulator is to:

A: Keep the color of the flame constant

B: Keep the high limit switch from tripping

C: Maintain a constant gas pressure at the burner

D: Allow the gas valve to operate smoothly and accurately

C: Maintain a constant gas pressure at the burner

The instrument used to measure outlet gas pressure is the:

A: Velometer

B: Anemometer

C: Monometer

D: Draft gauge

C: Monometer

The regulator on a natural gas furnace should be adjusted to supply _____ inches of pressure at the burners.

A: 11"

B: 10"

C: 3.5"

D: 2"

C: 3.5"

Burning one cubic foot of natural gas releases approximately _____ btu.

A: 800

B: 1,050

C: 12,000

D: 15,000

B: 1,050

Under ideal conditions natural gas has an ignition temperature of _______ degrees F and a burning temperature of ________ degrees F.

A: 800 degrees, 1000 degrees

B: 1,100 degrees, 3,500 degrees

C: 1,100 degrees, 5,000 degrees

D: 2,500 degrees, 8,000 degrees

B: 1,100 degrees, 3,500 degrees

Propane and butane are both:

A: Lighter than air

B: Heavier than air

C: Weigh the same as air

D: None of the above

B: Heavier than air

In order to achieve complete combustion with natural gas, each cubic foot of gas must combine with no less than ______ cubic feet of air with an additional 5 cubic feet of extra air to ensure there is enough oxygen for complete combustion.

A: 5 cubic feet
B: 10 cubic feet
C: 15 cubic feet
D: 20 cubic feet

B: 10 cubic feet

The three elements of combustion are:

A: Fuel, oxygen and ignition

B: Nitrogen, oxygen and heat

C: Air, fuel and oxygen

D: Air, fuel and nitrogen

A: Fuel, oxygen and ignition

Which of the following is a natural result of combustion?

A: Water vapor

B: Carbon monoxide

C: Carbon dioxide

D: All of the above

A: Water vapor

Primary air is air that:

A: Is mixed with the fuel before the fuel reaches the burner

B: Is mixed with the fuel at the burner after the fuel has ignited

C: Remains unused after the combustion process is complete

D: Enters the draft diverter and goes up the stack with the products of combustion

A: Is mixed with the fuel before the fuel reaches the burner

Secondary air is air that:

A: Is mixed with the fuel before the fuel reaches the burner

B: Is mixed with the fuel at the burner after the fuel has ignited

C: Remains unused after the combustion process is complete

D: Enters the draft diverter and goes up the stack with the products of combustion

B: Is mixed with the fuel at the burner after the fuel has ignited

The three major furnace configurations are:

A: Up-flow, down-flow and lowboy

B: Up-flow, down-flow and horizontal

C: Up-flow, down-flow and cross-flow

D: None of these is correct

B: Up-flow, down-flow and horizontal

Residential gas furnaces use blowers powered by which types of motors?

A: Poly-phase, two phase, single phase and capacitor start

B: Shaded pole, split-phase, capacitor start and PSC

C: Three phase, shaded pole and PSC

D: Split-phase, induction start-induction run and variable speed DC

D: Split-phase, induction start-induction run and variable speed DC

The horsepower range of residential heating blower motors is:

A: 1⁄8 to 1⁄16 hp

B: 1⁄4 to 1⁄2 hp

C: 1⁄2 to 2 hp

D: 3⁄4 to 2 hp

B: 1⁄4 to 1⁄2 hp

A heat anticipator is wired:

A: In series with the "W" terminal

B: In parallel with the "W" terminal

C: In series with the "R" terminal

D: In parallel with the "R" terminal

A: In series with the "W" terminal

Placing a jumper wire between the "R" terminal and the "G" terminal on a thermostat subbase will energize the:

A: Gas valve

B: Indoor fan motor

C: Outdoor fan motor

D: Compressor

B: Indoor fan motor

Placing a jumper wire between the "R" terminal and the "W" terminal on a thermostat sub-base will energize the:

A: Gas valve

B: Indoor fan motor

C: Outdoor fan motor

D: Compressor

A: Gas valve

Carbon monoxide is a:

A: Product of incomplete combustion

B: Poisonous gas

C: Odorless gas

D: All of the above are correct

D: All of the above are correct

The chemical symbol for carbon monoxide is:

A: CO2

B: CO

C: H2O

D: NH3

B: CO

Selecting a lower speed tap setting on a furnace indoor blower motor will cause:

A: The temperature rise through the furnace to increase

B: The temperature rise through the furnace to decrease

C: The temperature rise through the furnace will not be affected

D: The furnace to act as a humidifier

A: The temperature rise through the furnace to increase

"Carry over" channels or "cross overs" are used to:

A: Carry unused excess fuel back to the flue where it is sent up the stack

B: Carry primary air to the heat exchanger

C: Carry secondary air to the heat exchanger

D: Carry the flame from the first burner that lights to the remaining burners

D: Carry the flame from the first burner that lights to the remaining burners

Modern high-efficiency burners use combustion blowers. What are the two major types of combustion blowers?

A: Induced draft and forced draft

B: High pressure and low pressure

C: Impeller type and centrifugal type

D: Liquid and vapor types

A: Induced draft and forced draft

The purpose of the combustion blower is to:

A: Cause an adequate amount of oxygen-rich air to mix with the fuel for better combustion

B: Push the products of combustion out of the building

C: Prevent carbon monoxide from entering the heat exchanger

D: Give the larger blower motor a rest

A: Cause an adequate amount of oxygen-rich air to mix with the fuel for better combustion

Heat transfers from an object or area at a higher temperature to an object or area at a lower temperature. A heated heat exchanger transfers heat to the air by:

A: Conduction

B: Natural convection

C: Radiation

D: Forced convection

D: Forced convection

The voltage that creates a spark on a spark ignition system is approximately:

A: 240 volts

B: 5,000 volts

C: 15,000 volts

D: 25,000 volts

C: 15,000 volts

The capacity of a natural gas furnace is de-rated by _______ for every 1000 feet above sea level:

A: 1%

B: 2%

C: 3%

D: 4%

D: 4%

A crack in a heat exchanger can:

A: Allow combustion gases to mix with the space air

B: Prevent the heat from effectively transferring to the air

C: Cause the high-limit control to shut the furnace down

D: Cause the furnace to catch on fire

A: Allow combustion gases to mix with the space air

Gas valves operate on what voltage?

A: 12 volts

B: 24 volts

C: 120 volts

D: 230 volts

B: 24 volts

Mid-efficiency furnaces operate with flue gas temperatures between:

A: 275 and 360 degrees

B: 200 and 500 degrees

C: 100 and 275 degrees

D: 80 and 100 degrees

A: 275 and 360 degrees

High-efficiency furnaces operate with flue gas temperatures between:

A: 275 and 360 degrees

B: 200 and 500 degrees

C: 100 and 275 degrees

D: 80 and 100 degrees

C: 100 and 275 degrees

"B" vent is:

A: Hard, inflexible white plastic vent tubing able to withstand temperatures up to 325 degrees F

B: Hard, inflexible white plastic vent tubing able to withstand temperatures up to 400 degrees F

C: Single wall sheet metal vent pipe

D: Double wall sheet metal vent pipe

D: Double wall sheet metal vent pipe

Latent heat is:

A: Heat that causes a change in temperature with no change in state

B: Heat that causes a change in state with no change in temperature

C: The large amount of heat involved when a gas condenses into a liquid

D: Both b and c are correct

D: Both b and c are correct

A mid-efficiency or high-efficiency furnace will not operate if:

A: It is not grounded or the polarity is reversed

B: The indoor blower motor capacitor is wired into the wrong motor winding

C: The air filter is installed backwards

D: The door switch is shorted closed

A: It is not grounded or the polarity is reversed

Furnaces are placed into categories based upon:

A: Venting characteristics

B: Btuh capacity range

C: Gas valve type

D: Total airflow in CFM

A: Venting characteristics

Condensing furnaces:

A: Condense water vapor out of the air at the burner, thus increasing the efficiency of the burn

B: Increase the combustion efficiency by adding condensed oxygen to the fuel

C: Squeeze heat out of the flue gases by removing the latent heat of condensation causing much of it to liquefy

D: None of the above is correct

C: Squeeze heat out of the flue gases by removing the latent heat of condensation causing much of it to liquefy

Secondary heat exchangers:

A: optional heat exchangers used when necessary

B: constructed so return air passes over the secondary heat exchanger first and then over the main heat exchanger

C: used to add more heat to the supply air before entering the sheet metal ducting system

D: now rarely used on the higher efficiency furnaces

B: constructed so return air passes over the secondary heat exchanger first and then over the main heat exchanger

A combination fan-stat and high limit:

A: Are both safety controls

B: Consists of a high temperature safety thermostat built into the wall thermostat

C: Separate switches from a single helical bimetal, one switch controls the indoor fan, the other acting as safety control

D: All the above are correct

C: Separate switches from a single helical bimetal, one switch controls the indoor fan, the other acting as safety control

The three basic categories of ignition systems are:

A: Continuous ignition, intermittent ignition and direct ignition

B: Continuous ignition, direct ignition and manual ignition

C: Automatic ignition, intermittent ignition and direct ignition

D: Automatic ignition, direct ignition and indirect ignition

A: Continuous ignition, intermittent ignition and direct ignition

The intermittent ignition system:

A: Lights the burner directly

B: Uses a thermocouple

C: Lights the pilot only on a call for heat

D: Is the most efficient ignition system

C: Lights the pilot only on a call for heat

Direct ignition:

A: Uses a spark or hot surface igniter to light the burner directly

B: Gets its name from the fact that it is immediate, direct or fast acting

C: Lights the pilot only on a call for ignition

D: Is the most efficient ignition system

A: Uses a spark or hot surface igniter to light the burner directly

The flame sensor:

A: Is a thick ceramic rod that senses the heat of the flame and causes the rod to expand and signal the solid state flame board that a flame is present
B: Is a small-diameter conducting rod that senses when a flame is present because a current flow moves between the rod and the burner when the flame creates an electrical path between them
C: Is actually a metal-oxide diode that rectifies alternating current to direct current for the gas valve
D: Is a device that shuts down the main gas valve if the burner flame gets out of control and starts burning outside the fire box or combustion chamber

B: Is a small-diameter conducting rod that senses when a flame is present because a current flow moves between the rod and the burner when the flame creates an electrical path between them

Which of the following is a typical sequence of operation for a high efficiency condensing furnace?

A: induced draft blower runs for 20 seconds, ignitor heats for 15 seconds, gas valve opens, burner lights off, flame sensor monitors the flame for the entire heating cycle until the thermostat is satisfied
B: ignitor heats up for 15 seconds, gas valve opens and induced draft blower starts, burner lights and then flame sensor takes over monitoring until the thermostat is satisfied
C: induced draft blower runs for 20 seconds, ignitor heats up for 15 seconds, gas valve opens, burner lights off and flame sensor monitors flame. Plenum heats up, blower pulls air over the heat exchanger
D: None of these is correct, as condensing furnaces do not use induced draft blowers.

C: induced draft blower runs for 20 seconds, ignitor heats up for 15 seconds, gas valve opens, burner lights off and flame sensor monitors flame. Plenum heats up, blower pulls air over the heat exchanger

A yellow burner flame is usually caused by:

A: A weak ignitor

B: Lack of sufficient air

C: Low gas pressure

D: Too much primary air

B: Lack of sufficient air

A lifting burner flame is usually caused by:

A: A new ignitor that has not been broken in

B: High gas pressure and/or too much primary air

C: Low gas pressure and/or not enough primary air

D: Blockage in the flue

B: High gas pressure and/or too much primary air

What is the purpose of "timing a gas meter"?

A: To determine the actual input in Btuh of the furnace

B: To determine if the gas meter is accurate

C: To check the output of the gas valve

D: To test for carbon monoxide

A: To determine the actual input in Btuh of the furnace

Electrical troubleshooting of a furnace is best accomplished with a:

A: Pictorial wiring diagram

B: Photographs

C: Voltmeter

D: Both a and c

D: Both a and c

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