NATE (North American Technician Excellence) Certification — Questions and Answers

Question 1: What component in an induced-draft furnace proves that combustion airflow is established before the gas valve opens?

Limit switch
Thermocouple
Rollout switch
Pressure switch (Correct answer)

Correct answer: Pressure switch

The pressure switch senses negative pressure created by the inducer motor to confirm draft is established before allowing ignition.

Question 2: What is the purpose of a zone damper in a zoned HVAC system?

Balance static pressure across all zones simultaneously
Modulate the blower speed
Open or close to direct conditioned air to specific zones based on thermostat demand (Correct answer)
Filter air entering a specific zone

Correct answer: Open or close to direct conditioned air to specific zones based on thermostat demand

Zone dampers are motorized dampers controlled by zone thermostats that open to allow airflow to calling zones and close for non-calling zones.

Question 3: What outdoor temperature indicates a heat pump may need a 'cold climate' or variable-speed model to remain effective?

Below 0°F (Correct answer)
Below 50°F
Below 32°F
Below 20°F

Correct answer: Below 0°F

Standard heat pumps lose significant capacity below 32°F, while cold-climate models maintain heating capacity down to -13°F or lower.

Question 4: What does a smoke tester (Bacharach pump) measure on an oil burner?

Carbon soot level in flue gases by comparing a filter paper sample to a standard scale (Correct answer)
Stack gas CO2 percentage
Combustion air temperature
Oil pump pressure

Correct answer: Carbon soot level in flue gases by comparing a filter paper sample to a standard scale

The smoke tester draws flue gas through filter paper; the resulting stain is compared to a numbered scale (0 = clean, 9 = heavy smoke).

Question 5: What does a high discharge temperature on a refrigeration compressor typically indicate?

Low compression ratio
High compression ratio due to high head pressure, low suction pressure, or high superheat (Correct answer)
Overcharged refrigerant
Properly operating system

Correct answer: High compression ratio due to high head pressure, low suction pressure, or high superheat

High discharge temperature (above 225°F for most systems) results from high compression ratios or excessive superheat entering the compressor.

Question 6: What type of venting is required for a 96% AFUE condensing gas furnace?

Masonry chimney with liner
PVC plastic pipe for both flue and combustion air (Correct answer)
Category IV stainless steel vent
Type B double-wall vent

Correct answer: PVC plastic pipe for both flue and combustion air

High-efficiency condensing furnaces produce cool, moist flue gases that must be exhausted through PVC pipe; Category IV designation.

Question 7: At what temperature range does a medium-temperature refrigeration system typically maintain a reach-in display case?

-10°F to 0°F
0°F to 10°F
28°F to 40°F (Correct answer)
45°F to 55°F

Correct answer: 28°F to 40°F

Medium-temperature refrigeration maintains product temperatures between 28°F and 40°F for dairy, deli, and produce applications.

Question 8: What is subcooling in an air conditioning system?

Reducing condenser fan speed
Cooling the suction line below ambient
Number of degrees liquid refrigerant is cooled below its saturation temperature (Correct answer)
Lowering the thermostat setpoint

Correct answer: Number of degrees liquid refrigerant is cooled below its saturation temperature

Subcooling measures how many degrees the liquid refrigerant has been cooled below its condensing saturation temperature.

Question 9: When a heat pump is in heating mode and the emergency heat is energized, what happens?

The outdoor fan runs at high speed
The reversing valve switches to cooling mode
Both the compressor and electric strips run simultaneously
Only electric resistance strips provide heat; the compressor is locked out (Correct answer)

Correct answer: Only electric resistance strips provide heat; the compressor is locked out

Emergency heat bypasses the heat pump compressor and relies solely on electric resistance heat strips, typically used when the heat pump has failed.

Question 10: What is the correct procedure when a gas leak is suspected at a furnace?

Do not use any electrical switches; leave the building and call the gas company (Correct answer)
Apply pipe dope and continue operating the furnace
Turn on exhaust fans and relight the pilot
Increase gas pressure to identify the leak location

Correct answer: Do not use any electrical switches; leave the building and call the gas company

Any electrical switch operation could ignite accumulated gas; evacuate immediately and contact the gas utility from outside.

Question 11: What does ACCA Manual D provide for HVAC installations?

Commissioning and startup procedures
Procedures for residential duct system design and sizing (Correct answer)
Equipment selection guidelines
Indoor air quality standards

Correct answer: Procedures for residential duct system design and sizing

Manual D provides the calculations and procedures for designing duct systems that deliver the correct airflow to each room based on Manual J loads.

Question 12: What is the purpose of the Schrader valve on a refrigeration system?

Controls refrigerant flow rate
Regulates compressor speed
Prevents refrigerant from reversing direction
Provides a service port for pressure measurement and refrigerant access (Correct answer)

Correct answer: Provides a service port for pressure measurement and refrigerant access

Schrader valves are spring-loaded service ports that allow gauges and charging equipment to connect to the system.

Question 13: Which component on a heat pump prevents refrigerant from backing up into the compressor during the off cycle?

Check valve
Reversing valve
Filter drier
Accumulator (Correct answer)

Correct answer: Accumulator

The accumulator collects liquid refrigerant on the suction side during shutdown and prevents liquid slugging when the compressor restarts.

Question 14: What condition is indicated when an air conditioner's evaporator coil is heavily iced over?

Excessive outdoor ambient temperature
System is overcharged with refrigerant
Low airflow or low refrigerant charge (Correct answer)
High indoor humidity

Correct answer: Low airflow or low refrigerant charge

Restricted airflow or low refrigerant charge causes the evaporator to drop below freezing, leading to ice formation.

Question 15: What does a #2 fuel oil supply line's two-pipe system accomplish compared to a single-pipe system?

Provides redundancy if the primary supply fails
Filters water from the oil supply
Increases oil flow rate to the burner
Returns unused oil to the tank, preventing vapor lock and allowing the tank to be below the burner (Correct answer)

Correct answer: Returns unused oil to the tank, preventing vapor lock and allowing the tank to be below the burner

A two-pipe system continuously circulates oil back to the tank, preventing air and vapor buildup and allowing a below-burner tank installation.

Question 16: What condition does a very high return static pressure typically indicate?

Refrigerant overcharge
Excessive supply air
Oversized ductwork
Restricted return airflow due to clogged filter, blocked return grilles, or undersized return duct (Correct answer)

Correct answer: Restricted return airflow due to clogged filter, blocked return grilles, or undersized return duct

High return static pressure means the system is starved for return air, which reduces airflow and increases strain on the blower.

Question 17: What is the function of the rollout switch on a gas furnace?

Control the inducer motor speed
Measure gas manifold pressure
Monitor supply air temperature
Detect flame rollout and shut down the furnace if heat exceeds safe limits near the burner compartment (Correct answer)

Correct answer: Detect flame rollout and shut down the furnace if heat exceeds safe limits near the burner compartment

Rollout switches are manual-reset thermal devices that trip if flames exit the burner compartment, indicating a serious combustion problem.

Question 18: What is the purpose of a high-pressure cutout switch in an HVAC system?

Regulate low-side pressure
Protect the compressor from excessive discharge pressure (Correct answer)
Monitor suction line temperature
Limit refrigerant charge

Correct answer: Protect the compressor from excessive discharge pressure

A high-pressure cutout switch opens the control circuit when discharge pressure exceeds a safe limit, protecting the compressor from damage.

Question 19: Which type of furnace venting uses a dedicated fresh-air intake pipe running alongside the flue pipe?

Natural draft venting
Direct vent (sealed combustion) system (Correct answer)
Type B common vent
Power vent system

Correct answer: Direct vent (sealed combustion) system

Direct vent sealed-combustion furnaces draw all combustion air from outside through a dedicated intake, preventing depressurization of the home.

Question 20: LP (propane) gas manifold pressure for residential furnaces is typically set to which value?

3.5 inches WC
10–14 inches WC
0.5 PSI
7–11 inches WC (Correct answer)

Correct answer: 7–11 inches WC

Propane furnaces require higher manifold pressure than natural gas, typically 10–11 inches WC, because propane has different combustion characteristics.

Question 21: When measuring AC voltage with a multimeter, what type of reading does a standard digital multimeter display?

Peak-to-peak voltage
Peak voltage
Average voltage
RMS (root mean square) voltage (Correct answer)

Correct answer: RMS (root mean square) voltage

Standard digital multimeters display RMS voltage, which represents the effective value of AC voltage equivalent to DC.

Question 22: What is the maximum recommended duct velocity for residential supply ducts to minimize noise?

700–900 FPM (Correct answer)
1,200–1,500 FPM
2,000+ FPM
400–600 FPM

Correct answer: 700–900 FPM

Residential supply ducts typically target 700–900 FPM to balance duct size with acceptable noise levels.

Question 23: What is the minimum clearance from combustibles required for Type B vent pipe in most residential applications?

No clearance required
6 inches
3 inches
1 inch (Correct answer)

Correct answer: 1 inch

Type B double-wall vent pipe requires only 1-inch clearance from combustible materials due to its insulating outer jacket.

Question 24: What is the correct response when the oil burner primary control goes to hard lockout?

Press the reset button once after verifying the cause; repeated resets flood the combustion chamber with oil (Correct answer)
Call the gas company
Immediately press the reset button multiple times to restart
Replace the cad cell without pressing reset

Correct answer: Press the reset button once after verifying the cause; repeated resets flood the combustion chamber with oil

Pressing reset repeatedly without diagnosing the cause pumps unburned oil into the combustion chamber, creating a dangerous puffback hazard.

Question 25: What condition does a high CO2 reading combined with a high smoke number indicate on a combustion analysis?

Low oil pump pressure
Too little combustion air (rich mixture causing incomplete combustion) (Correct answer)
Too much combustion air (lean mixture)
Perfect combustion efficiency

Correct answer: Too little combustion air (rich mixture causing incomplete combustion)

High CO2 with high smoke indicates insufficient air, producing a rich mixture with incomplete combustion and carbon soot.

Question 26: What causes water in the oil tank and what is its effect on the burner?

Humidity in the combustion air dissolves into the fuel; causes nozzle clogging only
Condensation inside the tank accumulates water at the bottom; water can be drawn into the burner causing flame-outs and pump damage (Correct answer)
Only a tank leak allows water entry; it dilutes the oil reducing BTU output
Hot oil lines cause steam condensation; water has no effect on burner operation

Correct answer: Condensation inside the tank accumulates water at the bottom; water can be drawn into the burner causing flame-outs and pump damage

Condensation inside the tank introduces water that sinks to the bottom and can be drawn to the burner, causing hard lockouts and corrosion.

Question 27: What type of ignition system uses a glowing ceramic element to ignite the gas burners in modern furnaces?

Standing pilot
Spark ignition
Hot surface igniter (HSI) (Correct answer)
Direct spark ignition

Correct answer: Hot surface igniter (HSI)

Hot surface igniters heat to approximately 1800–2500°F using electricity to ignite the gas burner, replacing standing pilots.

Question 28: At what outdoor temperature do most standard air-source heat pumps reach their balance point?

25°F
50°F
35–40°F (Correct answer)
40°F

Correct answer: 35–40°F

The balance point is typically 35–40°F, where the heat pump output equals the building heat loss and auxiliary heat is not yet needed.

Question 29: What is the purpose of a filter-drier in a refrigeration system?

Reduce system sound levels
Remove moisture and contaminants from the refrigerant circuit (Correct answer)
Regulate refrigerant mass flow
Increase subcooling of liquid refrigerant

Correct answer: Remove moisture and contaminants from the refrigerant circuit

The filter-drier contains desiccant that absorbs moisture and a filter screen that traps particulates to protect the metering device and compressor.

Question 30: When charging a system with R-410A, the refrigerant cylinder should be held in which orientation?

Upright for vapor, inverted for liquid (Correct answer)
Upright only
Any position works
Upside down

Correct answer: Upright for vapor, inverted for liquid

R-410A must be charged as a liquid (cylinder inverted through a valve) to maintain the correct blend ratio.

Question 31: Which component in an air conditioning system is responsible for rejecting heat to the outdoors?

Evaporator
Condenser (Correct answer)
Expansion valve
Compressor

Correct answer: Condenser

The condenser releases heat absorbed from the indoor air to the outdoor environment.

Question 32: What percentage of CO2 in flue gas typically represents near-ideal combustion for a #2 oil burner?

11–13% (Correct answer)
15–17%
8–10%
5–7%

Correct answer: 11–13%

CO2 levels of 11–13% indicate near-stoichiometric combustion with minimal excess air and good efficiency for #2 fuel oil.

Question 33: What is the AFUE rating and what does it measure for a gas furnace?

Annual Fuel Utilization Efficiency; measures what percentage of fuel energy is converted to heat (Correct answer)
Annual Flue Utilization Effectiveness
Average Furnace Unit Efficiency; measures BTU output
Airflow Factor Under Extreme conditions

Correct answer: Annual Fuel Utilization Efficiency; measures what percentage of fuel energy is converted to heat

AFUE expresses as a percentage how much of the fuel's energy is converted to usable heat; a 96% AFUE furnace wastes only 4% up the flue.

Question 34: What initiates a defrost cycle on an air-source heat pump?

Compressor high-pressure lockout
Time/temperature or pressure differential control sensing frost buildup on outdoor coil (Correct answer)
Outdoor ambient thermostat dropping below 32°F
Indoor thermostat calling for auxiliary heat

Correct answer: Time/temperature or pressure differential control sensing frost buildup on outdoor coil

Defrost controls typically use a combination of time and outdoor coil temperature (or pressure differential) to trigger defrost when frost accumulates.

Question 35: What is the standard gas manifold pressure for natural gas residential furnaces in the US?

0.5–1.0 PSI
10–12 inches WC
7–14 inches WC
3.2–3.8 inches WC (Correct answer)

Correct answer: 3.2–3.8 inches WC

Natural gas furnace manifold pressure is typically set at 3.2–3.8 inches water column (around 3.5 inches WC nominal).

Question 36: What is the purpose of a hot gas defrost system in commercial refrigeration?

Melt frost from evaporator coils by circulating hot discharge gas through them instead of using electric heaters (Correct answer)
Prevent condensation on the case glass doors
Reheat supply air after cooling
Warm the compressor oil at startup

Correct answer: Melt frost from evaporator coils by circulating hot discharge gas through them instead of using electric heaters

Hot gas defrost diverts discharge gas from the compressor into the evaporator to melt frost quickly and efficiently without electric heaters.

Question 37: What is the primary reason refrigerant recovery is required before opening a sealed refrigeration system?

To comply with EPA Section 608 and prevent refrigerant release into the atmosphere (Correct answer)
To check refrigerant purity
To reduce system pressure for safe service
To remove moisture from the circuit

Correct answer: To comply with EPA Section 608 and prevent refrigerant release into the atmosphere

EPA Section 608 prohibits knowingly venting refrigerants; recovery captures refrigerant before system access.

Question 38: What is the function of the oil separator in a commercial refrigeration system?

Regulate oil temperature
Remove moisture from refrigerant
Separate compressor oil from the discharge gas and return it to the compressor crankcase (Correct answer)
Filter non-condensables from the system

Correct answer: Separate compressor oil from the discharge gas and return it to the compressor crankcase

Oil separators prevent excessive oil migration through the system, ensuring the compressor maintains adequate lubrication.

Question 39: What unit is used to measure duct air leakage during a duct leakage test?

MERV rating
Grains per pound
CFM25 (cubic feet per minute at 25 pascals) (Correct answer)
Inches WC

Correct answer: CFM25 (cubic feet per minute at 25 pascals)

Duct leakage is expressed as CFM25, the airflow escaping through duct leaks when pressurized to 25 pascals above atmospheric pressure.

Question 40: What is a bypass damper used for in a zoned duct system?

Balance airflow between supply and return plenums
Control humidity in a single zone
Provide fresh outdoor air to the return system
Relieve excess static pressure when zone dampers close by routing air back to the return side (Correct answer)

Correct answer: Relieve excess static pressure when zone dampers close by routing air back to the return side

When zone dampers close, the bypass damper opens to maintain minimum airflow across the coil and prevent equipment damage from excessive static pressure.

Question 41: What does a low suction pressure reading typically indicate in a residential AC system?

Overcharge of refrigerant
Faulty discharge valve
Condenser fan failure
Low refrigerant charge or restricted airflow (Correct answer)

Correct answer: Low refrigerant charge or restricted airflow

Low suction pressure usually points to insufficient refrigerant or reduced evaporator airflow causing lower evaporating temperatures.

Question 42: What type of duct fitting causes the most turbulence and pressure drop?

Long-radius elbow
Square elbow without turning vanes (Correct answer)
Straight section
Conical reducer

Correct answer: Square elbow without turning vanes

Sharp square elbows cause severe turbulence and high pressure drop; long-radius elbows or elbows with turning vanes greatly reduce this loss.

Question 43: Which EPA section requires technicians to be certified before purchasing refrigerants?

Section 406
Section 302
Section 410
Section 608 (Correct answer)

Correct answer: Section 608

EPA Section 608 regulations require HVAC technicians to be certified when purchasing and handling refrigerants.

Question 44: What does the ASHRAE 62.2 standard address in residential applications?

Duct leakage limits for new construction
Ventilation and acceptable indoor air quality for residential buildings (Correct answer)
Minimum equipment efficiency ratings
Duct system design procedures

Correct answer: Ventilation and acceptable indoor air quality for residential buildings

ASHRAE 62.2 specifies minimum mechanical ventilation rates to maintain acceptable indoor air quality in residences.

Question 45: On a cooling thermostat, which terminals are energized when the system is calling for cooling?

R and G
R and Y (Correct answer)
R and O
R and W

Correct answer: R and Y

During a cooling call, the Y (compressor) terminal is energized along with R (power), activating the compressor contactor.

Question 46: What is the correct method for measuring total external static pressure (TESP) on an air handler?

Measure velocity pressure at the blower inlet
Measure only at the supply plenum
Average pressures at all supply registers
Measure static pressure in the return plenum before the coil and in the supply plenum after the coil, then subtract return from supply (Correct answer)

Correct answer: Measure static pressure in the return plenum before the coil and in the supply plenum after the coil, then subtract return from supply

TESP = supply static pressure minus return static pressure (both measured close to the air handler), giving total system resistance.

Question 47: What is the function of the delayed oil valve (solenoid valve) on some oil burners?

Prevent oil flow during power outages
Allow oil to flow only on a call for heat
Stop oil flow immediately on burner shutdown to prevent after-drip and after-fire (Correct answer)
Regulate oil pressure during high-fire mode

Correct answer: Stop oil flow immediately on burner shutdown to prevent after-drip and after-fire

The delayed oil valve closes instantly when the burner shuts off, preventing oil drip into the combustion chamber that could cause after-fire and smoke.

Question 48: What annual maintenance item is most critical for oil burner efficiency?

Replacing the nozzle and cleaning the strainer, electrodes, and heat exchanger (Correct answer)
Adjusting the thermostat anticipator
Flushing the oil tank
Replacing the transformer

Correct answer: Replacing the nozzle and cleaning the strainer, electrodes, and heat exchanger

An annual tune-up including nozzle replacement and cleaning ensures complete combustion, maximum efficiency, and safe operation.

Question 49: What is the function of the cad cell (cadmium sulfide cell) in an oil burner primary control?

Monitor stack temperature
Control the firing rate of the burner
Measure oil pump pressure
Sense the presence or absence of a flame by its resistance to light (Correct answer)

Correct answer: Sense the presence or absence of a flame by its resistance to light

The cad cell changes resistance based on light; in darkness (no flame) its high resistance signals the primary control to initiate lockout.

Question 50: What MERV rating range is recommended for residential HVAC filters to balance filtration and airflow?

5–8 (Correct answer)
14–16
1–4
9–13

Correct answer: 5–8

MERV 5–8 filters provide adequate filtration for residential equipment while maintaining sufficient airflow and avoiding excessive pressure drop.

Question 51: What does a suction line accumulator protect in a refrigeration system?

Expansion device from debris
Liquid line from high pressure
Compressor from liquid refrigerant slugging (Correct answer)
Condenser from excess load

Correct answer: Compressor from liquid refrigerant slugging

The accumulator traps liquid refrigerant on the suction line, boiling it off slowly rather than allowing it to enter and damage the compressor.

Question 52: What is the primary control's 'safety timing' function on an oil furnace?

Allow a limited time for ignition then shut down the burner if no flame is proven (Correct answer)
Control circulator pump timing
Purge the combustion chamber before ignition
Prevent the burner from firing more than 3 times per hour

Correct answer: Allow a limited time for ignition then shut down the burner if no flame is proven

Safety timing (typically 45–90 seconds) limits how long unburned oil can accumulate before locking out the burner to prevent explosion.

Question 53: What is flash gas and where does it occur in the refrigeration cycle?

Gas released from compressor oil at high temperature
Refrigerant that vaporizes as pressure drops across the metering device before reaching the evaporator (Correct answer)
Hot discharge gas from the compressor
Vapor formed in the condenser

Correct answer: Refrigerant that vaporizes as pressure drops across the metering device before reaching the evaporator

Flash gas forms when liquid refrigerant loses pressure at the metering device, absorbing no useful heat and reducing system capacity.

Question 54: What is the purpose of a liquid line solenoid valve in a refrigeration system?

Prevent liquid refrigerant from returning to the compressor
Stop refrigerant flow to the evaporator when the thermostat is satisfied or during pump-down (Correct answer)
Regulate refrigerant pressure in the liquid line
Control condensing fan speed

Correct answer: Stop refrigerant flow to the evaporator when the thermostat is satisfied or during pump-down

A liquid line solenoid valve closes on a thermostat-off signal, stopping refrigerant flow and allowing the compressor to pump down the evaporator.

Question 55: What is the effect of duct leakage in unconditioned spaces like attics and crawlspaces?

Has negligible effect on system performance
Only affects humidity levels
Wastes significant conditioned air to outside, dramatically increasing energy consumption and reducing comfort (Correct answer)
Slightly increases equipment run time

Correct answer: Wastes significant conditioned air to outside, dramatically increasing energy consumption and reducing comfort

Leaking supply ducts in unconditioned spaces lose conditioned air to outside while leaking return ducts pull hot/cold unconditioned air into the system.

Question 56: What is Manual J used for in residential HVAC design?

Sizing expansion valves
Duct sizing calculations
Selecting refrigerant type
Calculating heating and cooling loads for a structure (Correct answer)

Correct answer: Calculating heating and cooling loads for a structure

ACCA Manual J is the industry-standard load calculation procedure that determines the BTU capacity required to heat and cool a home.

Question 57: What is the refrigeration effect and how is it calculated?

Heat absorbed in the evaporator; calculated as evaporator outlet enthalpy minus evaporator inlet enthalpy (Correct answer)
Heat rejected at the condenser; calculated as condenser enthalpy minus compressor inlet enthalpy
Work input to the compressor
Heat gained by subcooling the liquid line

Correct answer: Heat absorbed in the evaporator; calculated as evaporator outlet enthalpy minus evaporator inlet enthalpy

The refrigeration effect is the heat absorbed per pound of refrigerant in the evaporator, equal to the enthalpy difference across the evaporator.

Question 58: What EPA regulation governs refrigerant handling and requires recovery before service of commercial refrigeration equipment?

EPA Section 608 (Correct answer)
OSHA 29 CFR 1910
EPA Section 404
Clean Water Act

Correct answer: EPA Section 608

EPA Section 608 prohibits venting refrigerants and requires certified technicians to recover refrigerant before opening any refrigerant circuit.

Question 59: What is the function of a run capacitor in a PSC (permanent split capacitor) motor?

Improve power factor and running efficiency (Correct answer)
Protect against overcurrent
Store energy during power outages
Provide starting torque only

Correct answer: Improve power factor and running efficiency

A run capacitor creates a phase shift in the auxiliary winding that improves power factor and running efficiency throughout operation.

Question 60: What does a TXV (thermostatic expansion valve) use to control refrigerant flow?

Condenser outlet temperature
Suction line superheat sensed by a bulb (Correct answer)
Discharge pressure
Liquid line subcooling

Correct answer: Suction line superheat sensed by a bulb

A TXV senses evaporator outlet superheat via a sensing bulb and adjusts flow to maintain a set superheat.

Question 61: What refrigerant is used in low-temperature frozen food applications and has an evaporating temperature around -20°F?

R-404A or R-448A (Correct answer)
R-134a
R-410A
R-22

Correct answer: R-404A or R-448A

R-404A and its replacement R-448A are designed for low and medium-temperature commercial refrigeration systems.

Question 62: What is the purpose of the electrodes in an oil burner?

Sense the flame via rectification
Control oil pump speed
Measure flue gas temperature
Produce a high-voltage spark to ignite the atomized oil-air mixture (Correct answer)

Correct answer: Produce a high-voltage spark to ignite the atomized oil-air mixture

Electrodes are positioned in the air-oil spray and produce a continuous or intermittent spark to ignite the mixture at startup.

Question 63: What is the recommended insulation R-value for ducts installed in unconditioned attics in most US climate zones?

R-6
R-4
R-8 (Correct answer)
R-11

Correct answer: R-8

Most US energy codes and ACCA guidelines recommend R-8 duct insulation for ducts in unconditioned attic spaces to minimize heat gain or loss.

Question 64: A motor draws 8 amps at 240V. What is the approximate power consumption in watts?

2,400 watts
1,920 watts (Correct answer)
960 watts
1,200 watts

Correct answer: 1,920 watts

Power (W) = Voltage × Current = 240V × 8A = 1,920 watts for a single-phase resistive load.

Question 65: What is the typical oil pump pressure setting for a residential oil burner?

200–300 PSI
50–60 PSI
25–40 PSI
100–150 PSI (Correct answer)

Correct answer: 100–150 PSI

Residential oil burner pumps typically operate at 100–150 PSI (commonly 100 PSI) to properly atomize the fuel through the nozzle.

Question 66: What is a common symptom of a stuck reversing valve in the heating position?

Both A and C (Correct answer)
Compressor short cycles
System heats normally but will not cool
Outdoor coil ices over in summer

Correct answer: Both A and C

A reversing valve stuck in heating mode causes the system to heat when cooling is called for, and the outdoor coil may ice in summer because it acts as an evaporator.

Question 67: What is the function of a crankcase heater on a compressor?

Increase compressor speed at startup
Prevent refrigerant from migrating into the compressor oil during off cycles (Correct answer)
Warm the discharge line in winter
Heat the outdoor coil to prevent frost

Correct answer: Prevent refrigerant from migrating into the compressor oil during off cycles

Crankcase heaters keep compressor oil warm to prevent refrigerant absorption and potential liquid slugging on startup.

Question 68: What does a cracked heat exchanger in a gas furnace risk introducing into the living space?

Carbon monoxide (CO) and other combustion byproducts (Correct answer)
Refrigerant vapor
Nitrogen dioxide only
Natural gas from the supply line

Correct answer: Carbon monoxide (CO) and other combustion byproducts

Cracks in the heat exchanger allow combustion gases including deadly carbon monoxide to mix with circulated air and enter the living space.

Question 69: What is the purpose of the metering device in a refrigeration circuit?

Compress the refrigerant
Filter moisture from the refrigerant
Reduce refrigerant pressure and control flow into the evaporator (Correct answer)
Remove heat from the condenser

Correct answer: Reduce refrigerant pressure and control flow into the evaporator

The metering device reduces high-pressure liquid refrigerant to low-pressure liquid/vapor, controlling flow into the evaporator.

Question 70: What is the purpose of the vent pressure switch on a two-stage condensing furnace?

Verify combustion air is being supplied
Confirm the inducer is operating at proper speed and the vent is clear before allowing ignition (Correct answer)
Control secondary heat exchanger temperature
Monitor return air static pressure

Correct answer: Confirm the inducer is operating at proper speed and the vent is clear before allowing ignition

The vent pressure switch proves adequate draft by sensing the negative pressure created by the inducer blower before the gas valve is energized.

Question 71: Which wire color in a standard NEC-compliant 120V residential wiring system is the grounded conductor (neutral)?

Black
Green
White (Correct answer)
Red

Correct answer: White

Per NEC, white (or gray) is the grounded conductor (neutral) in a standard 120V residential wiring system.

Question 72: Which component in an HVAC control circuit is used to sense thermostat demand and energize the compressor contactor?

Capacitor
Thermistor
Control relay (Correct answer)
Transformer

Correct answer: Control relay

A control relay receives the low-voltage thermostat signal and switches the higher-voltage circuit to energize the compressor contactor.

Question 73: What is the typical target evaporator superheat range for a fixed-orifice metering device system?

0–5°F
25–40°F
10–18°F (Correct answer)
5–10°F

Correct answer: 10–18°F

A fixed-orifice system typically targets 10–18°F of superheat at the evaporator outlet for proper refrigerant feed.

Question 74: What causes a high compression ratio in a refrigeration system?

High suction superheat only
High condensing pressure and/or low evaporating pressure (Correct answer)
Low ambient temperature
Oversized metering device

Correct answer: High condensing pressure and/or low evaporating pressure

Compression ratio is head pressure divided by suction pressure; it rises when the condenser is hot (high head) or evaporator is cold (low suction).

Question 75: What is the recommended duct sealing material for permanent duct repairs?

Spray foam insulation
Standard gray cloth duct tape
Silicone caulk
Mastic sealant or metal foil tape (UL 181 listed) (Correct answer)

Correct answer: Mastic sealant or metal foil tape (UL 181 listed)

Mastic sealant and UL 181 listed foil tape are durable, code-approved methods; standard cloth duct tape dries out and fails over time.

Question 76: What does a barometric draft control (draft regulator) do in an oil heating system?

Prevent flue gases from entering the living area
Maintain constant flue draft by admitting dilution air when draft exceeds setpoint (Correct answer)
Boost flue draft in low-pressure conditions
Control combustion air to the burner

Correct answer: Maintain constant flue draft by admitting dilution air when draft exceeds setpoint

The barometric damper swings open to admit room air when draft is too strong, maintaining a stable negative pressure in the flue.

Question 77: What does superheat measure in a refrigeration system?

Temperature of liquid refrigerant leaving the condenser
Temperature rise of vapor above the saturation point at a given pressure (Correct answer)
Subcooling at the condenser outlet
Compressor discharge temperature

Correct answer: Temperature rise of vapor above the saturation point at a given pressure

Superheat is the number of degrees the refrigerant vapor temperature exceeds the saturation temperature at that pressure.

Question 78: What is the purpose of a balancing damper in a duct branch?

Filter particulates from the airstream
Prevent backdrafting
Reduce duct noise
Adjust airflow to individual zones to balance the system and deliver correct CFM to each room (Correct answer)

Correct answer: Adjust airflow to individual zones to balance the system and deliver correct CFM to each room

Balancing dampers restrict airflow in over-supplied branches, diverting more air to under-supplied areas for proper room-by-room comfort.

Question 79: What does a megohmmeter (megger) measure?

Contactor coil impedance
Insulation resistance of motor windings (Correct answer)
Capacitor microfarad rating
AC line frequency

Correct answer: Insulation resistance of motor windings

A megohmmeter applies high DC voltage to measure insulation resistance, revealing breakdown or moisture in motor windings.

Question 80: What component allows a heat pump to reverse the refrigeration cycle between heating and cooling modes?

Accumulator
Check valve
Thermostatic expansion valve
Reversing valve (Correct answer)

Correct answer: Reversing valve

The reversing valve redirects refrigerant flow so the indoor coil acts as a condenser in heating mode and an evaporator in cooling mode.

Question 81: What is a condensate drain trap used for on a high-efficiency furnace?

Trap combustion gases before they exit
Filter particulates from the condensate water
Reduce drain line vibration
Prevent flue gases from backing up through the condensate drain while allowing water to drain freely (Correct answer)

Correct answer: Prevent flue gases from backing up through the condensate drain while allowing water to drain freely

The condensate trap maintains a water seal that blocks furnace gases from escaping through the drain while permitting condensate to flow out.

Question 82: Which tool is used to measure the wet-bulb temperature when evaluating air conditioning performance?

Sling psychrometer (Correct answer)
Clamp meter
Manifold gauge set
Anemometer

Correct answer: Sling psychrometer

A sling psychrometer uses a wet-bulb and dry-bulb thermometer to measure relative humidity and wet-bulb temperature.

Question 83: What is the purpose of the heat exchanger in a gas furnace?

Mix combustion gases with supply air
Remove moisture from combustion products
Transfer heat from combustion gases to the circulating air without mixing them (Correct answer)
Regulate gas pressure to the burners

Correct answer: Transfer heat from combustion gases to the circulating air without mixing them

The heat exchanger keeps combustion products separated from conditioned air while allowing heat transfer through the metal walls.

Question 84: Which type of compressor uses scroll technology and is common in modern residential AC units?

Reciprocating
Centrifugal
Screw
Scroll (Correct answer)

Correct answer: Scroll

Scroll compressors use two interlocking spirals and are favored in residential equipment for efficiency and quiet operation.

Question 85: What is the minimum SEER2 requirement for a new split-system AC unit installed in the US Southeast after January 1, 2023?

15 SEER2
14 SEER2 (Correct answer)
16 SEER2
13 SEER2

Correct answer: 14 SEER2

The US Department of Energy set the minimum SEER2 efficiency standard at 14 for split systems in the Southeast and Southwest regions effective January 2023.

Question 86: A furnace high-limit switch trips repeatedly. What is the most common cause?

Dirty air filter or restricted airflow causing the heat exchanger to overheat (Correct answer)
Low gas pressure
Gas valve is stuck open
Faulty thermostat

Correct answer: Dirty air filter or restricted airflow causing the heat exchanger to overheat

Restricted airflow from a clogged filter or blocked supply/return prevents adequate heat dissipation, causing heat exchanger temperatures to exceed the limit switch setpoint.

Question 87: What is the primary safety device that shuts off the gas valve if the pilot flame is extinguished on a standing pilot furnace?

Thermocouple (Correct answer)
Limit switch
Flame sensor rod
Pressure switch

Correct answer: Thermocouple

The thermocouple generates a small millivolt signal that holds the gas valve open; when the pilot goes out the signal drops and the valve closes.

Question 88: Which type of transformer is commonly used to step down 240V line voltage to 24V for HVAC control circuits?

Current transformer
Step-up transformer
Step-down isolation transformer (Correct answer)
Autotransformer

Correct answer: Step-down isolation transformer

A step-down isolation transformer reduces line voltage (240V) to the 24V AC required by HVAC control circuits.

Question 89: What component in an oil burner atomizes the fuel oil and mixes it with air for combustion?

Oil pump
Electrodes
Cad cell
Nozzle (Correct answer)

Correct answer: Nozzle

The nozzle atomizes oil into a fine spray at a precise angle and pattern, mixing it with combustion air for efficient burning.

Question 90: What does the flame sensor do in a modern electronic ignition furnace?

Passes a small DC current through the flame to prove ignition and keep the gas valve open (Correct answer)
Measures combustion air temperature
Controls burner gas pressure
Monitors heat exchanger temperature

Correct answer: Passes a small DC current through the flame to prove ignition and keep the gas valve open

The flame sensor uses flame rectification—the ionized flame allows DC current to flow—proving the burner is lit and preventing gas buildup.

Question 91: What tool is used to measure air velocity in a duct or at a register?

Psychrometer
Combustion analyzer
Anemometer or flow hood (Correct answer)
Manometer

Correct answer: Anemometer or flow hood

An anemometer measures air velocity in feet per minute (FPM); a flow hood captures total CFM at a register directly.

Question 92: A high-efficiency split system AC rated at SEER 18 performs better than a unit rated at which of the following?

SEER 21
SEER 16 (Correct answer)
SEER 20
SEER 19

Correct answer: SEER 16

SEER (Seasonal Energy Efficiency Ratio) measures cooling efficiency; higher numbers indicate better efficiency.

Question 93: What does HSPF2 measure for a heat pump?

Defrost cycle frequency
Compressor efficiency ratio
Heating efficiency measured as total heat output divided by total electrical energy over the heating season (Correct answer)
Cooling efficiency over a season

Correct answer: Heating efficiency measured as total heat output divided by total electrical energy over the heating season

HSPF2 (Heating Seasonal Performance Factor 2) rates heating efficiency; higher values indicate more efficient heating performance.

Question 94: What does external static pressure (ESP) measure in an HVAC duct system?

Return air CO2 concentration
Total resistance to airflow the blower must overcome, measured in inches of water column (Correct answer)
Velocity of air at the supply registers
Duct leakage to outside

Correct answer: Total resistance to airflow the blower must overcome, measured in inches of water column

ESP is the sum of supply and return static pressures and indicates how hard the blower works against the duct system resistance.

Question 95: What does a sight glass with bubbles in the liquid line typically indicate?

System is operating normally
Overcharged system
Insufficient refrigerant charge or restriction causing flashing in the liquid line (Correct answer)
Excessive superheat

Correct answer: Insufficient refrigerant charge or restriction causing flashing in the liquid line

Bubbles in the sight glass indicate incomplete condensation; the liquid line is carrying a vapor-liquid mixture, signaling low charge or a restriction.

Question 96: What color should the burner flame be on a properly adjusted natural gas furnace?

Red/orange
Pure white
Mostly blue with slight yellow tips (Correct answer)
Yellow/orange with tips

Correct answer: Mostly blue with slight yellow tips

A properly burning natural gas flame should be predominantly blue, indicating complete combustion, with minor yellow tips acceptable.

Question 97: A heat pump's outdoor unit is making a hissing noise and the reversing valve solenoid is energized. What is the most likely cause?

Refrigerant leak at the reversing valve
Defrost board failure
Overcharged refrigerant system
Reversing valve internal bypass (leaking internally) (Correct answer)

Correct answer: Reversing valve internal bypass (leaking internally)

An internally leaking reversing valve allows high-pressure refrigerant to bypass to the low-pressure side, causing a hissing sound.

Question 98: What annual efficiency rating measures the seasonal performance of an oil furnace?

COP
EER
SEER
AFUE (Correct answer)

Correct answer: AFUE

AFUE (Annual Fuel Utilization Efficiency) measures the percentage of fuel converted to heat over the heating season for oil furnaces.

Question 99: What refrigerant is most commonly used in modern residential air conditioning systems in the US?

R-134a
R-22
R-404A
R-410A (Correct answer)

Correct answer: R-410A

R-410A replaced R-22 as the standard residential AC refrigerant due to R-22's ozone-depleting properties.

Question 100: What is the standard line voltage for most residential HVAC equipment in the United States?

120V/60Hz
208V/60Hz
240V/60Hz (Correct answer)
277V/60Hz

Correct answer: 240V/60Hz

Most residential HVAC equipment in the US operates on 240V single-phase 60Hz power.

NATE (North American Technician Excellence) Certification

The NATE certification exam validates HVAC technician knowledge and skills across specialty areas including air conditioning, heat pumps, gas heating, oil heating, and air distribution systems. Technicians must demonstrate competency in installation and service/troubleshooting to earn industry-recognized NATE credentials.

Questions

35 min

Time Limit

70%

To Pass

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These practice questions were written with AI tools. They are not real exam questions. Exam facts are checked against the official sources listed below. Not reviewed by a subject-matter expert. Editorial policy

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natex.org — Fees, retake policy, score validity, renewal, passing score, score release, test dates, exam format, time limit, eligibility · verified Oct 2026