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NATE_HEATPUMP_SERVICE NEC 2023

NATE Heat Pump Service Practice Test 8

This test covers dual-fuel (hybrid) heat pump systems — how a heat pump pairs with a gas furnace as backup instead of electric strips, and how the control strategy decides which one runs.

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NATE Heat Pump Service

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Frequently Asked Questions

Yes — completely free with no signup required. Every question includes a full explanation of the correct answer.

Two: the NATE Core exam plus at least one specialty exam (for example AC Service, Heat Pump Service, or Air Distribution Service). You can take them on the same day or separately.

The Core exam has 50 questions and each installation or service specialty exam has 100 questions. You need 70% on each to pass — 35 of 50 on Core and 70 of 100 on a specialty. Check natex.org for the current format before you book.

NATE certification lasts two years. To renew, you submit 16 hours of continuing education or retake the specialty exam before your certification expires.

No. These are independent practice tests written to match the published NATE exam topics. They are not official NATE exam questions.

Exam Tip: A dual-fuel system switches to gas heat below a set outdoor temperature (or based on a cost comparison) — know why, not just that it happens.

30

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30 min

Time

70%

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NATE Heat Pump Service Practice Test 8 — Question List

Question 1: What is a dual-fuel (hybrid) heating system?

A heat pump paired with a gas furnace as backup heat instead of electric strips
Two heat pumps installed side by side
A furnace that burns two different types of gas
A heat pump with two separate compressors

Question 2: Why might a dual-fuel system switch to the gas furnace instead of running electric strips at low outdoor temperatures?

Gas heat may be more cost-effective than electric-strip backup at very low temperatures
Electric strips cannot legally be used below freezing
The heat pump compressor is destroyed by cold weather
Gas furnaces produce more noise, which is preferred in winter

Question 3: What commonly triggers a dual-fuel system to switch from heat pump to gas furnace operation?

A set outdoor temperature threshold, or a cost-efficiency comparison programmed into the control
The indoor thermostat display color
The time of day only, regardless of temperature
The refrigerant charge level alone

Question 4: In mild weather, which heat source does a dual-fuel system typically use?

The gas furnace only, all year
The heat pump, since it is generally more efficient in moderate outdoor temperatures
Electric strips only, all year
Neither source runs in mild weather

Question 5: What role does a dual-fuel control board (or compatible thermostat) play in the system?

It decides which heat source to call based on the programmed strategy and current conditions
It only controls the indoor blower speed
It has no role — both sources always run together
It only controls the outdoor condenser fan

Question 6: A dual-fuel system is found running the heat pump compressor and the gas furnace burner at the same time during normal operation. Is this expected?

Yes, this is always normal and by design
No — a properly functioning dual-fuel control should generally run one heat source at a time, not both simultaneously
Yes, but only in the summer
No, but only because the thermostat batteries are low

Question 7: What is a key advantage of a dual-fuel system over a straight heat pump with electric-strip backup in a cold climate?

Gas heat can supply strong heating output efficiently at very low temperatures, where electric strips are more expensive to run
Gas furnaces never require any maintenance
Gas heat eliminates the need for a thermostat
Electric strips cannot produce any heat below freezing

Question 8: On a dual-fuel system, what would "emergency heat" mode typically mean if the heat pump has failed?

Running only the gas furnace directly, bypassing the heat pump entirely
Shutting off all heat sources completely
Running the heat pump compressor at double speed
Switching to cooling mode instead of heating

Question 9: A customer complains the gas furnace never runs even in very cold weather, and the heat pump struggles to keep up. What should a technician check first?

The dual-fuel control settings and outdoor temperature sensor/threshold programming
The condenser fan motor only
The indoor air filter only
The refrigerant color

Question 10: What is the difference between a temperature-based and a cost-based dual-fuel switchover strategy?

Temperature-based switches at a fixed outdoor temperature; cost-based compares the running cost of each fuel and switches when one becomes cheaper
They are two names for the exact same strategy
Temperature-based ignores outdoor temperature entirely
Cost-based only works with electric strips, never gas

Question 11: Why does a dual-fuel system typically need a thermostat or control specifically designed for dual-fuel operation?

It must coordinate calls to two different heat sources (heat pump and furnace) rather than just one
Dual-fuel systems do not use a thermostat at all
Any thermostat works identically regardless of system type
It is only needed to control the condenser fan speed

Question 12: During a heat pump defrost cycle on a dual-fuel system, what commonly happens to avoid blowing cold air indoors?

The gas furnace (rather than electric strips) can be used to temporarily supply indoor heat during defrost
Nothing changes — cold air is always blown regardless of system type
The compressor is permanently shut off for the rest of the season
The outdoor fan runs at maximum speed during defrost

Question 13: Why does a heat pump's efficiency advantage shrink as outdoor temperature drops, making the dual-fuel comparison relevant?

There is less available heat in colder outdoor air for the heat pump to extract, lowering its COP
The heat pump's refrigerant freezes solid below 32°F
The heat pump automatically shuts off below 50°F on every system
Colder air has no effect on heat pump performance

Question 14: True or False: On a dual-fuel system, the automatic switchover to the gas furnace based on outdoor temperature is the same thing as manually selecting "emergency heat."

True
False
Only true on gas-only systems
Only true in summer

Question 15: What does a dual-fuel system mean for a technician's maintenance visit compared to a straight heat pump system?

The technician needs to check and maintain both the heat pump and the gas furnace, plus the switchover control logic
There is nothing extra to check compared to a straight heat pump
Only the thermostat needs to be checked, nothing else
Dual-fuel systems never need maintenance

Question 16: A customer notices the gas furnace runs even on mild days when the heat pump should easily be able to keep up. What is a likely cause?

The switchover threshold may be set too high (calling for gas too early), or a heat pump fault is causing it to underperform
This is always intentional and needs no investigation
The gas furnace is broken and stuck on
The thermostat has no bearing on this behavior

Question 17: Does the gas furnace side of a dual-fuel system share the same refrigerant circuit as the heat pump?

Yes, they share one combined refrigerant circuit
No — the furnace uses a separate combustion/heat-exchanger process with no refrigerant involved
The furnace runs entirely on refrigerant instead of gas
There is no real difference between the two heat sources

Question 18: In cooling mode, how does a dual-fuel system's heat pump typically operate compared to a straight heat pump system?

The same — cooling mode operation is unaffected by the presence of the gas furnace backup
The furnace assists with cooling by blowing cold combustion air
Cooling mode is disabled on all dual-fuel systems
The compressor runs backward in cooling mode on dual-fuel systems

Question 19: How can a technician verify a dual-fuel system's switchover point is working as programmed?

Check the control's programmed setting against the current outdoor temperature and observe which source is actually running
There is no way to verify this without replacing the whole system
Only the manufacturer can verify switchover behavior
Switchover cannot be checked without disconnecting the furnace permanently

Question 20: A dual-fuel system is set to switch to gas below 35°F. It is currently 40°F outside and the furnace is running while the heat pump sits idle. What should the technician investigate?

Why the furnace is running above the programmed switchover temperature, such as a control fault, wrong sensor reading, or incorrect programming
Nothing, this is completely normal and expected
The refrigerant charge is definitely low
The thermostat batteries are definitely dead

Question 21: Since a dual-fuel system includes a gas furnace, what safety-related system does a technician also need to check that a straight heat pump does not have?

The combustion venting and gas supply system
The refrigerant recovery cylinder color
The indoor thermostat batteries only
Nothing additional is ever needed

Question 22: Why might the ideal switchover point differ between two different customers' dual-fuel systems in the same city?

Local utility rates for electricity and gas can differ between customers or change over time, affecting the cost-based comparison
All dual-fuel systems are legally required to use the exact same switchover point
Switchover points never vary between installations
Only the equipment brand determines the switchover point, never cost

Question 23: Does a dual-fuel system's heat pump still use a reversing valve the same way a straight heat pump does?

Yes — the heat pump portion of a dual-fuel system still uses a reversing valve to switch between heating and cooling mode
No, dual-fuel heat pumps never use a reversing valve
The reversing valve is replaced by the furnace burner
The reversing valve only works when the furnace is also running

Question 24: How does the concept of a heat pump's balance point relate to setting a dual-fuel switchover temperature?

The switchover temperature is often set at or near the heat pump's balance point, where it can no longer keep up alone
Balance point and switchover temperature are completely unrelated concepts
The balance point only applies to cooling mode
The balance point is always exactly 0°F on every system

Question 25: Summarize in one idea: what problem does a dual-fuel system solve that a straight heat pump with electric strips does not?

It gives a more cost-effective and efficient backup heat option for very cold weather
It eliminates the need for a compressor entirely
It removes the need for a thermostat
It has no advantage over electric-strip backup

Question 26: Why does the gas furnace in a dual-fuel system need to be properly sized for the building, just like the heat pump?

An undersized or oversized furnace can cause the same comfort and efficiency problems as an improperly sized standalone furnace
Furnace sizing does not matter since it is only a backup
The furnace never needs to be sized, only the heat pump does
Furnace size only affects the price, not performance

Question 27: Does adding a gas furnace to a heat pump system change what refrigerant the heat pump uses?

No — the refrigerant used depends on the heat pump itself, not on whether it is paired with a furnace
Yes, dual-fuel systems always require a special refrigerant
Yes, the furnace supplies refrigerant to the heat pump
Dual-fuel heat pumps do not use refrigerant at all

Question 28: Why might a technician need to reference the specific equipment's wiring diagram more carefully on a dual-fuel installation than on a straight heat pump?

There are more control wires and interlocks coordinating two heat sources, increasing wiring complexity
Dual-fuel systems actually have simpler wiring than any other system
Wiring diagrams are not available for dual-fuel systems
Dual-fuel systems use no low-voltage control wiring at all

Question 29: Why does the outdoor temperature sensor's placement matter for a temperature-based dual-fuel switchover strategy?

A poorly placed sensor (e.g., in direct sun or near a heat source) can give an inaccurate reading, causing the switchover to happen at the wrong time
Sensor placement never affects the reading in any way
The sensor is only decorative and not used in switchover logic
Sensor placement only matters for cooling mode

Question 30: Which of these is a true statement about dual-fuel heat pump systems?

Both heat sources always run together at all times
The heat pump and furnace are coordinated by a control strategy so that generally only one heat source runs at a time
The furnace replaces the reversing valve
Dual-fuel systems cannot be used with electric utilities

EXAM CARD NATE_HEATPUMP_SERVICE

Questions30

Time limit30 min

Pass score70%

Code editionNEC 2023

DifficultyIntermediate

Last reviewedJun 2026

Timer starts immediately. Progress is auto-saved.

Source: NEC 2026 (NFPA 70)