1
NATE Gas Heating Exam Actual Exam 2026/2027:
Comprehensive Multiple Choice Questions with
Verified & Revised Answers for HVAC Excellence –
Pass Guaranteed - A+ Graded
SECTION 1: Gas Furnace Components & Operation (12 questions)
Q1: In a modern condensing gas furnace with a 95% AFUE rating, which component extracts
additional heat from combustion gases to achieve high efficiency?
A. Primary heat exchanger only
B. Secondary heat exchanger (condensing heat exchanger)
C. Draft inducer motor only
D. Hot surface ignitor
Correct Answer: B
Rationale: Condensing furnaces (90%+ AFUE) utilize a secondary heat exchanger constructed
of stainless steel or aluminized steel that extracts latent heat from combustion gases by cooling
them below their dew point (approximately 130°F), causing water vapor to condense and release
additional heat. The primary heat exchanger (A) operates similarly to standard furnaces. The
draft inducer (C) maintains proper venting pressure but doesn't extract heat. The HSI (D) is for
ignition only. Per NATE KATEs and ANSI Z21.47, this secondary extraction distinguishes
condensing from non-condensing designs. [CORRECT]
Q2: Which ignition system uses a silicon carbide or silicon nitride element that heats to
approximately 1,800-2,500°F to ignite gas when energized?
A. Intermittent pilot ignition
B. Direct spark ignition
C. Hot surface ignition (HSI)
D. Standing pilot ignition
Correct Answer: C
Rationale: Hot surface ignition (HSI) systems use a resistive ceramic element (silicon carbide or
silicon nitride) that glows white-hot when 80-120V is applied, directly igniting the gas at the
burners. This is the most common modern ignition method per ANSI Z21.47. Intermittent pilot
(A) uses a spark to light a pilot that then lights main burners. Direct spark ignition (B) sparks
directly at the main burner. Standing pilot (D) maintains a continuous pilot flame. [CORRECT]
,2
Q3: During the heating cycle of a furnace with hot surface ignition, which sequence occurs after
the draft inducer proves operation via the pressure switch?
A. Gas valve opens immediately, then HSI energizes
B. HSI energizes and heats for 30-45 seconds, then gas valve opens
C. Blower starts immediately, then HSI energizes
D. Limit switch closes, then gas valve opens
Correct Answer: B
Rationale: Per NATE KATEs and ANSI Z21.47 sequence of operation: (1) Thermostat calls for
heat, (2) Draft inducer starts, (3) Pressure switch proves inducer operation, (4) HSI energizes for
warm-up period (30-45 seconds), (5) Gas valve opens, (6) Flame is established and sensed, (7)
Blower starts after time delay or temperature rise. The HSI must reach ignition temperature
before gas flows to prevent delayed ignition and flashback. [CORRECT]
Q4: Which safety device monitors combustion rollout—flames escaping the burner
compartment—and requires manual reset after tripping?
A. Draft safeguard switch
B. Rollout limit switch (auxiliary limit)
C. Pressure switch
D. Fan limit control
Correct Answer: B
Rationale: Rollout limit switches (auxiliary limits) are mounted on the burner compartment or
heat exchanger flange to detect flame rollout caused by blocked flues, cracked heat exchangers,
or overfiring. These bimetal switches open at typically 300-350°F and require manual reset to
ensure the technician investigates the cause. Draft safeguard (A) monitors inducer pressure.
Pressure switches (C) prove inducer operation. Fan limits (D) control blower operation based on
plenum temperature. [CORRECT]
Q5: In a two-stage gas furnace, which component modulates gas flow between high and low
fire?
A. Single-speed draft inducer
B. Two-stage gas valve with dual solenoids or modulating pressure regulator
C. Variable-speed blower motor only
D. Thermocouple
, 3
Correct Answer: B
Rationale: Two-stage furnaces utilize a gas valve with dual solenoid valves or a modulating
pressure regulator that switches between approximately 40-70% (low fire) and 100% (high fire)
input rates based on thermostat demand and control board logic. The draft inducer (A) may be
multi-speed but doesn't modulate gas flow. The blower (C) modulates airflow, not gas flow.
Thermocouples (D) are safety sensors, not control devices. Per ANSI Z21.47 and NATE KATEs,
staged gas valves enable efficiency and comfort improvements. [CORRECT]
Q6: Which component in a condensing furnace collects and drains acidic condensate produced
during high-efficiency combustion?
A. Primary heat exchanger drain
B. Condensate trap and drain system
C. Draft inducer drain
D. Blower compartment drain
Correct Answer: B
Rationale: Condensing furnaces produce acidic condensate (pH 3-5) from combustion
byproducts cooling below dew point. A condensate trap (P-trap or internal trap) prevents flue gas
escape while allowing drainage to a floor drain, pump, or neutralizer. The trap must maintain
water seal per NFGC and manufacturer specifications. Primary exchangers (A) don't produce
condensate. Inducer drains (C) may exist but aren't the primary collection. Blower compartments
(D) should remain dry. [CORRECT]
Q7: Which type of blower motor uses a variable frequency drive (VFD) or inverter technology to
precisely control airflow across multiple speeds for optimal efficiency and comfort?
A. Permanent split capacitor (PSC) motor
B. Standard shaded-pole motor
C. Electronically commutated motor (ECM) or variable-speed motor
D. Three-phase induction motor
Correct Answer: C
Rationale: ECMs (electronically commutated motors) or true variable-speed motors use DC
voltage with electronic commutation and often include VFD capability, allowing precise airflow
matching to system requirements (heating, cooling, dehumidification, continuous fan). PSC
motors (A) have fixed speeds based on winding taps. Shaded-pole motors (B) are single-speed,
low-torque. Three-phase motors (D) are industrial, not residential furnace blowers. Per NATE
KATEs, ECMs provide significant efficiency gains. [CORRECT]
NATE Gas Heating Exam Actual Exam 2026/2027:
Comprehensive Multiple Choice Questions with
Verified & Revised Answers for HVAC Excellence –
Pass Guaranteed - A+ Graded
SECTION 1: Gas Furnace Components & Operation (12 questions)
Q1: In a modern condensing gas furnace with a 95% AFUE rating, which component extracts
additional heat from combustion gases to achieve high efficiency?
A. Primary heat exchanger only
B. Secondary heat exchanger (condensing heat exchanger)
C. Draft inducer motor only
D. Hot surface ignitor
Correct Answer: B
Rationale: Condensing furnaces (90%+ AFUE) utilize a secondary heat exchanger constructed
of stainless steel or aluminized steel that extracts latent heat from combustion gases by cooling
them below their dew point (approximately 130°F), causing water vapor to condense and release
additional heat. The primary heat exchanger (A) operates similarly to standard furnaces. The
draft inducer (C) maintains proper venting pressure but doesn't extract heat. The HSI (D) is for
ignition only. Per NATE KATEs and ANSI Z21.47, this secondary extraction distinguishes
condensing from non-condensing designs. [CORRECT]
Q2: Which ignition system uses a silicon carbide or silicon nitride element that heats to
approximately 1,800-2,500°F to ignite gas when energized?
A. Intermittent pilot ignition
B. Direct spark ignition
C. Hot surface ignition (HSI)
D. Standing pilot ignition
Correct Answer: C
Rationale: Hot surface ignition (HSI) systems use a resistive ceramic element (silicon carbide or
silicon nitride) that glows white-hot when 80-120V is applied, directly igniting the gas at the
burners. This is the most common modern ignition method per ANSI Z21.47. Intermittent pilot
(A) uses a spark to light a pilot that then lights main burners. Direct spark ignition (B) sparks
directly at the main burner. Standing pilot (D) maintains a continuous pilot flame. [CORRECT]
,2
Q3: During the heating cycle of a furnace with hot surface ignition, which sequence occurs after
the draft inducer proves operation via the pressure switch?
A. Gas valve opens immediately, then HSI energizes
B. HSI energizes and heats for 30-45 seconds, then gas valve opens
C. Blower starts immediately, then HSI energizes
D. Limit switch closes, then gas valve opens
Correct Answer: B
Rationale: Per NATE KATEs and ANSI Z21.47 sequence of operation: (1) Thermostat calls for
heat, (2) Draft inducer starts, (3) Pressure switch proves inducer operation, (4) HSI energizes for
warm-up period (30-45 seconds), (5) Gas valve opens, (6) Flame is established and sensed, (7)
Blower starts after time delay or temperature rise. The HSI must reach ignition temperature
before gas flows to prevent delayed ignition and flashback. [CORRECT]
Q4: Which safety device monitors combustion rollout—flames escaping the burner
compartment—and requires manual reset after tripping?
A. Draft safeguard switch
B. Rollout limit switch (auxiliary limit)
C. Pressure switch
D. Fan limit control
Correct Answer: B
Rationale: Rollout limit switches (auxiliary limits) are mounted on the burner compartment or
heat exchanger flange to detect flame rollout caused by blocked flues, cracked heat exchangers,
or overfiring. These bimetal switches open at typically 300-350°F and require manual reset to
ensure the technician investigates the cause. Draft safeguard (A) monitors inducer pressure.
Pressure switches (C) prove inducer operation. Fan limits (D) control blower operation based on
plenum temperature. [CORRECT]
Q5: In a two-stage gas furnace, which component modulates gas flow between high and low
fire?
A. Single-speed draft inducer
B. Two-stage gas valve with dual solenoids or modulating pressure regulator
C. Variable-speed blower motor only
D. Thermocouple
, 3
Correct Answer: B
Rationale: Two-stage furnaces utilize a gas valve with dual solenoid valves or a modulating
pressure regulator that switches between approximately 40-70% (low fire) and 100% (high fire)
input rates based on thermostat demand and control board logic. The draft inducer (A) may be
multi-speed but doesn't modulate gas flow. The blower (C) modulates airflow, not gas flow.
Thermocouples (D) are safety sensors, not control devices. Per ANSI Z21.47 and NATE KATEs,
staged gas valves enable efficiency and comfort improvements. [CORRECT]
Q6: Which component in a condensing furnace collects and drains acidic condensate produced
during high-efficiency combustion?
A. Primary heat exchanger drain
B. Condensate trap and drain system
C. Draft inducer drain
D. Blower compartment drain
Correct Answer: B
Rationale: Condensing furnaces produce acidic condensate (pH 3-5) from combustion
byproducts cooling below dew point. A condensate trap (P-trap or internal trap) prevents flue gas
escape while allowing drainage to a floor drain, pump, or neutralizer. The trap must maintain
water seal per NFGC and manufacturer specifications. Primary exchangers (A) don't produce
condensate. Inducer drains (C) may exist but aren't the primary collection. Blower compartments
(D) should remain dry. [CORRECT]
Q7: Which type of blower motor uses a variable frequency drive (VFD) or inverter technology to
precisely control airflow across multiple speeds for optimal efficiency and comfort?
A. Permanent split capacitor (PSC) motor
B. Standard shaded-pole motor
C. Electronically commutated motor (ECM) or variable-speed motor
D. Three-phase induction motor
Correct Answer: C
Rationale: ECMs (electronically commutated motors) or true variable-speed motors use DC
voltage with electronic commutation and often include VFD capability, allowing precise airflow
matching to system requirements (heating, cooling, dehumidification, continuous fan). PSC
motors (A) have fixed speeds based on winding taps. Shaded-pole motors (B) are single-speed,
low-torque. Three-phase motors (D) are industrial, not residential furnace blowers. Per NATE
KATEs, ECMs provide significant efficiency gains. [CORRECT]
