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Question 1General HVAC Knowledge and Fundamentals

Which of the following best defines the purpose of a heating, ventilation, and air conditioning (HVAC) system?

  1. To control the temperature, humidity, air quality, and air movement within a space Correct answer.
  2. To increase the pressure of refrigerant in a closed loop
  3. To generate electricity for building operations
  4. To filter water used in hydronic heating

Explanation

HVAC systems are designed to provide indoor environmental comfort by regulating temperature, humidity, air cleanliness, and air circulation. They do not generate electricity, treat water, or primarily pressurize refrigerant as an end goal.

Question 2General HVAC Knowledge and Fundamentals

In the refrigeration cycle, which component is responsible for absorbing heat from the conditioned space?

  1. The expansion valve
  2. The compressor
  3. The evaporator Correct answer.
  4. The condenser

Explanation

The evaporator is where low-pressure refrigerant absorbs heat from the surrounding air or water, causing the refrigerant to evaporate. The condenser rejects heat, the compressor raises pressure, and the expansion valve meters refrigerant flow.

Question 3General HVAC Knowledge and Fundamentals

What is the primary function of the compressor in a vapor-compression refrigeration system?

  1. To condense refrigerant vapor into liquid
  2. To circulate refrigerant and raise its pressure and temperature Correct answer.
  3. To remove moisture from the refrigerant
  4. To lower the boiling point of the refrigerant

Explanation

The compressor draws in low-pressure vapor and compresses it, raising both pressure and temperature so the refrigerant can reject heat in the condenser. It does not directly condense the refrigerant or remove moisture.

Question 4General HVAC Knowledge and Fundamentals

Which of the following is a standard unit used to express the heating or cooling capacity of an HVAC system in the United States?

  1. British thermal unit per hour (Btu/h) Correct answer.
  2. Kilogram (kg)
  3. Liter per second (L/s)
  4. Pascal (Pa)

Explanation

Heating and cooling capacity is commonly expressed in Btu/h or tons of refrigeration (1 ton = 12,000 Btu/h). Pascals measure pressure, kilograms measure mass, and liters per second measure airflow.

Question 5General HVAC Knowledge and Fundamentals

What does the term 'ton of refrigeration' represent?

  1. The amount of heat required to melt one ton of ice in 24 hours
  2. The airflow rate needed to cool one ton of air
  3. The weight of refrigerant needed to fill a system
  4. The cooling capacity equal to 12,000 Btu/h Correct answer.

Explanation

One ton of refrigeration is defined as the rate of heat removal equivalent to melting one ton of ice at 32°F in 24 hours, which equals 12,000 Btu/h. It is a measure of capacity, not refrigerant weight or airflow.

Question 6General HVAC Knowledge and Fundamentals

Which of the following best describes sensible heat?

  1. Heat that causes a change in state without a temperature change
  2. Heat that causes a change in temperature of a substance Correct answer.
  3. Heat that is released during condensation
  4. Heat that is absorbed during evaporation

Explanation

Sensible heat is heat that changes the temperature of a substance and can be sensed by a thermometer. Latent heat, in contrast, causes a phase change without a temperature change.

Question 7General HVAC Knowledge and Fundamentals

What is the primary purpose of a thermostat in an HVAC system?

  1. To control the operation of heating and cooling equipment based on temperature Correct answer.
  2. To regulate the speed of the indoor blower
  3. To filter contaminants from the air stream
  4. To measure the humidity of the conditioned space

Explanation

A thermostat senses space temperature and signals the HVAC equipment to start or stop to maintain the desired setpoint. It does not directly measure humidity, filter air, or control blower speed (though some advanced thermostats can).

Question 8General HVAC Knowledge and Fundamentals

Which of the following is a common safety hazard associated with HVAC work?

  1. Exposure to refrigerant vapors Correct answer.
  2. Excessive lighting levels
  3. Low noise levels
  4. Overly humidified air

Explanation

Refrigerant vapors can displace oxygen and cause frostbite or poisoning, making them a significant hazard. High lighting, low noise, and humidified air are not typical safety hazards.

Question 9General HVAC Knowledge and Fundamentals

In a forced-air heating system, what is the function of the heat exchanger?

  1. To exhaust flue gases to the outdoors
  2. To transfer heat from the combustion gases to the supply air without mixing the two streams Correct answer.
  3. To filter dust particles from the return air
  4. To mix fuel with air for combustion

Explanation

The heat exchanger separates the combustion products from the air being heated, allowing heat transfer while preventing contamination of the supply air. Fuel mixing occurs in the burner, flue exhaust is handled by the vent, and filtration is separate.

Question 10General HVAC Knowledge and Fundamentals

What is the primary difference between a furnace and a boiler?

  1. A furnace heats air, while a boiler heats water or steam Correct answer.
  2. A furnace provides cooling, while a boiler provides heating
  3. A furnace is more efficient than a boiler
  4. A furnace uses electricity, while a boiler uses gas

Explanation

Furnaces distribute heated air through ducts, whereas boilers heat water or generate steam for hydronic or steam distribution systems. Fuel type and efficiency vary independently of this distinction.

Question 11General HVAC Knowledge and Fundamentals

Which of the following best describes the function of an air handler in an HVAC system?

  1. To burn fuel for heating
  2. To compress refrigerant vapor
  3. To control the humidity of the air
  4. To move conditioned air through the ductwork Correct answer.

Explanation

An air handler contains a blower and often a coil, filter, and other components to circulate conditioned air through ducts. It does not compress refrigerant, burn fuel, or directly control humidity (though it may house a coil that affects humidity).

Question 12General HVAC Knowledge and Fundamentals

What is the purpose of a condensate drain in a cooling system?

  1. To remove liquid water that condenses on the evaporator coil Correct answer.
  2. To supply water to the humidifier
  3. To release excess refrigerant pressure
  4. To drain refrigerant oil from the compressor

Explanation

As air passes over the cold evaporator coil, moisture condenses and must be drained away to prevent water damage and microbial growth. It does not handle refrigerant oil, pressure relief, or humidifier supply.

Question 13General HVAC Knowledge and Fundamentals

In a ducted HVAC system, what does the term 'static pressure' refer to?

  1. The resistance to airflow within the duct system Correct answer.
  2. The pressure exerted by the refrigerant in the coil
  3. The pressure of the gas supplied to the furnace
  4. The velocity of air moving through the duct

Explanation

Static pressure is the resistance that the duct system offers to airflow, measured in inches of water column. It is distinct from velocity pressure and from refrigerant or gas pressures.

Question 14General HVAC Knowledge and Fundamentals

Which of the following is a common method for measuring airflow in a duct?

  1. Using a thermometer to measure temperature difference
  2. Using a manometer to measure pressure drop across a coil Correct answer.
  3. Using a clamp meter to measure current
  4. Using a sling psychrometer

Explanation

A manometer measuring pressure drop across a component (like a coil) can be used with manufacturer data to determine airflow. Psychrometers measure humidity, clamp meters measure current, and thermometers measure temperature, not airflow directly.

Question 15General HVAC Knowledge and Fundamentals

What is the primary function of a filter in an HVAC system?

  1. To cool the air before it enters the coil
  2. To add moisture to the air
  3. To remove odors from the air
  4. To capture airborne particles and protect equipment Correct answer.

Explanation

Filters primarily capture dust, dirt, and other particles to protect the blower, coils, and ductwork and to improve indoor air quality. They are not designed for odor removal, humidification, or cooling.

Question 16General HVAC Knowledge and Fundamentals

Which of the following best describes the term 'dry-bulb temperature'?

  1. The temperature at which air becomes saturated
  2. The temperature of a surface exposed to airflow
  3. The temperature of air measured with a wet wick
  4. The temperature of air measured with a thermometer exposed to the air Correct answer.

Explanation

Dry-bulb temperature is the ordinary air temperature measured by a dry thermometer. Wet-bulb temperature uses a wet wick, and dew point is the saturation temperature.

Question 17General HVAC Knowledge and Fundamentals

What is the purpose of a humidistat in an HVAC system?

  1. To control the operation of heating equipment
  2. To measure the speed of the blower
  3. To measure and control humidity levels Correct answer.
  4. To detect refrigerant leaks

Explanation

A humidistat senses relative humidity and controls humidification or dehumidification equipment to maintain a desired humidity level. It does not control temperature, blower speed, or detect refrigerant leaks.

Question 18General HVAC Knowledge and Fundamentals

Which of the following is a correct statement about the relationship between airflow and heat transfer in an air conditioning system?

  1. Airflow has no effect on heat transfer
  2. Increasing airflow across the evaporator coil generally increases the heat transfer rate Correct answer.
  3. Airflow only affects the compressor, not the coil
  4. Decreasing airflow across the evaporator coil always increases the heat transfer rate

Explanation

Higher airflow across the evaporator coil increases the rate of heat transfer up to the point where the coil can no longer effectively dehumidify. Reduced airflow decreases heat transfer and can cause coil icing.

Question 19General HVAC Knowledge and Fundamentals

What is the function of a compressor in a heat pump system during the heating mode?

  1. It shuts off to allow the auxiliary heat to operate
  2. It raises the pressure and temperature of refrigerant vapor for heat rejection indoors Correct answer.
  3. It bypasses the outdoor coil to prevent freezing
  4. It reverses the refrigerant flow to act as an evaporator

Explanation

In heating mode, the compressor still raises refrigerant pressure and temperature, but the roles of the indoor and outdoor coils are reversed so heat is rejected indoors. A reversing valve changes refrigerant direction, not the compressor.

Question 20General HVAC Knowledge and Fundamentals

Which of the following best describes the purpose of a plenum in an HVAC duct system?

  1. To provide a large chamber for mixing or distributing air before it enters branch ducts Correct answer.
  2. To filter the air before it reaches the coil
  3. To regulate the refrigerant flow to the evaporator
  4. To distribute conditioned air to individual rooms

Explanation

A plenum is a box or chamber that connects the air handler or furnace to the duct distribution system, allowing air to mix and distribute evenly. Branch ducts handle room distribution, filters handle filtration, and metering devices regulate refrigerant.

Question 21General HVAC Knowledge and Fundamentals

What is the primary purpose of commissioning an HVAC system?

  1. To verify that the system operates as designed and meets specified performance criteria Correct answer.
  2. To obtain a building permit for the installation
  3. To repair any damage that occurred during installation
  4. To train the building occupants on system operation

Explanation

Commissioning is a quality assurance process that verifies and documents that systems are installed and operate according to the design intent and owner's requirements. It is not primarily for repairs, training, or permitting.

Question 22General HVAC Knowledge and Fundamentals

A technician measures a temperature difference of 18°F across the evaporator coil. If the airflow is 400 cfm per ton and the system capacity is 3 tons, what is the approximate sensible cooling capacity in Btu/h? (Use the sensible heat equation: Btu/h = 1.08 × cfm × ΔT)

  1. 36,000 Btu/h
  2. 12,960 Btu/h
  3. 23,328 Btu/h Correct answer.
  4. 6,480 Btu/h

Explanation

Total airflow = 3 tons × 400 cfm/ton = 1,200 cfm. Using the sensible heat equation: Btu/h = 1.08 × 1,200 × 18 = 23,328 Btu/h. This represents the sensible cooling capacity.

Question 23General HVAC Knowledge and Fundamentals

In a refrigeration cycle, if the condenser is not rejecting enough heat, what is the most likely effect on the system?

  1. Suction pressure decreases and the evaporator becomes colder
  2. The expansion valve opens wider to compensate
  3. Discharge pressure increases and the compressor may overheat Correct answer.
  4. The evaporator coil freezes due to low refrigerant flow

Explanation

Insufficient heat rejection at the condenser causes refrigerant to remain at higher pressure and temperature, raising discharge pressure and compressor load. This can lead to overheating and reduced system capacity.

Question 24General HVAC Knowledge and Fundamentals

Which of the following statements about latent heat and sensible heat in an air conditioning process is correct?

  1. Latent heat removal has no effect on the air's moisture content
  2. Sensible heat removal changes the moisture content of the air
  3. Sensible heat removal decreases the dry-bulb temperature, while latent heat removal decreases the moisture content Correct answer.
  4. Latent heat removal increases the dry-bulb temperature of the air

Explanation

Sensible cooling lowers the dry-bulb temperature without changing moisture content, while latent cooling removes moisture (dehumidification) without necessarily changing temperature. Together they determine the total cooling load.

Question 25General HVAC Knowledge and Fundamentals

A building requires 120,000 Btu/h of heating. A furnace is rated at 80% AFUE. What is the required input capacity of the furnace?

  1. 100,000 Btu/h
  2. 96,000 Btu/h
  3. 150,000 Btu/h Correct answer.
  4. 120,000 Btu/h

Explanation

Input capacity = Output capacity / AFUE = 120,000 / 0.80 = 150,000 Btu/h. The furnace must consume 150,000 Btu/h of fuel to deliver 120,000 Btu/h of heat.

Question 26General HVAC Knowledge and Fundamentals

At standard atmospheric pressure, at what temperature does pure water boil?

  1. 100°F
  2. 212°F Correct answer.
  3. 180°F
  4. 150°F

Explanation

At sea-level atmospheric pressure of about 14.7 psia, pure water boils at 212°F (100°C). Boiling point changes with pressure, rising above 212°F at higher pressures and falling below it at altitude.

Question 27General HVAC Knowledge and Fundamentals

In the refrigeration cycle, which component raises the pressure and temperature of the refrigerant vapor before it enters the condenser?

  1. The evaporator
  2. The accumulator
  3. The compressor Correct answer.
  4. The metering device

Explanation

The compressor takes low-pressure, low-temperature vapor and compresses it into high-pressure, high-temperature vapor that the condenser can then reject heat from. The metering device does the opposite, dropping pressure between the condenser and evaporator.

Question 28General HVAC Knowledge and Fundamentals

A technician reads 72°F dry-bulb and 60°F wet-bulb on a sling psychrometer. What does the difference between these two readings indicate?

  1. The refrigerant charge is low.
  2. The air is completely dry because the readings differ.
  3. The air contains some moisture, since wet-bulb is below dry-bulb. Correct answer.
  4. The relative humidity is 100%.

Explanation

Wet-bulb temperature drops below dry-bulb as water evaporates from the wet sock, and the size of that depression reflects how much moisture the air can still absorb. A wet-bulb equal to dry-bulb means saturation, while a large depression means drier air, so any measurable difference means the air holds some moisture but is not saturated.

Question 29General HVAC Knowledge and Fundamentals

A technician wants to confirm that a gas furnace is operating within its rated temperature rise. Which measurement set is required?

  1. Flue-gas temperature and combustion-air temperature
  2. Outdoor temperature and indoor temperature
  3. Refrigerant suction pressure and liquid-line pressure
  4. Supply-air temperature and return-air temperature Correct answer.

Explanation

Temperature rise is the difference between the supply-air temperature leaving the furnace and the return-air temperature entering it, compared against the rating plate range. This measurement confirms that airflow and firing rate are properly matched to the appliance.

Question 30General HVAC Knowledge and Fundamentals

A technician measures 30°F of subcooling on a system with a TXV and a normal refrigerant charge, but the condenser is clean and airflow is correct. Which condition best explains this reading?

  1. Liquid is backing up in the condenser, restricting flow at the metering device. Correct answer.
  2. The system is undercharged.
  3. The TXV is overfeeding the evaporator.
  4. The evaporator coil is frozen.

Explanation

Subcooling is the amount the liquid refrigerant is cooled below its condensing temperature, and it rises when liquid backs up in the condenser because the metering device or a restriction limits flow out of it. Excess subcooling with a clean condenser and correct airflow points to restricted liquid flow rather than a charge or evaporator problem.

Question 31Heating Systems and Equipment

In a conventional gas-fired forced-air furnace, what is the primary function of the draft inducer assembly?

  1. It pulls combustion gases through the heat exchanger and vents them outdoors Correct answer.
  2. It mixes return air with outdoor ventilation air before heating
  3. It circulates conditioned room air through the supply ductwork
  4. It regulates the manifold gas pressure delivered to the burners

Explanation

The draft inducer is a small blower mounted at the flue outlet that establishes negative pressure in the heat exchanger, drawing combustion products through and out the vent. Room-air circulation is handled by the separate blower assembly.

Question 32Heating Systems and Equipment

A technician measures 24 VAC at the gas valve terminals but the burners do not light and no gas odor is present. Which component should be checked first?

  1. The high-limit switch
  2. The draft inducer capacitor
  3. The flame sensor rod
  4. The gas valve operator and its outlet pressure Correct answer.

Explanation

Voltage present at the valve with no gas flow points to the valve itself failing to open or a gas supply problem at the valve. The flame sensor only matters after ignition occurs, and the high-limit would interrupt the 24 VAC signal.

Question 33Heating Systems and Equipment

Which type of heat exchanger is characteristic of a condensing furnace?

  1. A bare copper tube bundle inside the supply plenum
  2. A single cast-iron sectional boiler block
  3. A refractory-lined firebox with atmospheric burners
  4. A secondary stainless steel or polypropylene coil that extracts latent heat Correct answer.

Explanation

Condensing furnaces add a secondary heat exchanger downstream of the primary one to cool flue gases below the dew point, recovering latent heat. Cast-iron sections and refractory fireboxes are boiler and older furnace designs that do not condense.

Question 34Heating Systems and Equipment

A hot water boiler has a pressure-reducing (feed) valve set at 12 psig and a system relief valve set at 30 psig. The system is cold and reads 12 psig, but after firing the pressure climbs to 28 psig. What is the most likely cause?

  1. The circulator is running backwards
  2. The relief valve is stuck open
  3. The feed valve is set too low
  4. The expansion tank is waterlogged or the tank bladder has failed Correct answer.

Explanation

Pressure that rises sharply with temperature indicates the expansion tank can no longer absorb the volume increase, typically a waterlogged tank or ruptured bladder. A stuck-open relief valve would lower pressure, not raise it.

Question 35Heating Systems and Equipment

What is the purpose of the limit switch in a forced-air furnace?

  1. It senses flame current at the burner
  2. It closes the circuit to start the blower on a call for heat
  3. It maintains manifold gas pressure at the setpoint
  4. It opens the burner circuit if the heat exchanger overheats Correct answer.

Explanation

The high-limit is a safety device wired in series with the gas valve that opens on excessive temperature to stop combustion. Blower start is controlled by a fan switch or time delay, not the limit.

Question 36Heating Systems and Equipment

A technician is checking a standing-pilot gas furnace. The pilot lights but goes out when the knob is released. Which item is the most likely cause?

  1. An open blower door switch
  2. A failed hot surface igniter
  3. A weak or dirty thermocouple Correct answer.
  4. A clogged condensate trap

Explanation

A standing pilot relies on a thermocouple to hold the gas valve open; a weak or dirty thermocouple cannot generate enough millivoltage. Hot surface igniters and condensate traps belong to other ignition and condensing designs.

Question 37Heating Systems and Equipment

Which condition most directly indicates a cracked heat exchanger in a gas furnace?

  1. A steady manifold pressure reading
  2. A clean flame sensor signal
  3. A normal temperature rise across the furnace
  4. A change in flame pattern when the blower starts Correct answer.

Explanation

A crack allows supply air to disturb combustion, so the flame reacts when the blower energizes. Stable manifold pressure and normal temperature rise do not reveal a breach.

Question 38Heating Systems and Equipment

In a hydronic system, what is the function of an air separator?

  1. It separates condensate from flue gas
  2. It isolates the boiler from the system during service
  3. It separates supply and return piping in a manifold
  4. It removes entrained air from the circulating water Correct answer.

Explanation

An air separator uses low velocity and coalescing media to release entrained air so it can be vented. Isolation is done by valves, and condensate separation is a combustion concern.

Question 39Heating Systems and Equipment

A furnace nameplate shows a 60,000 BTU/h input and an 80% AFUE. Approximately how much heat is delivered to the conditioned space?

  1. 75,000 BTU/h
  2. 12,000 BTU/h
  3. 48,000 BTU/h Correct answer.
  4. 60,000 BTU/h

Explanation

Output equals input multiplied by efficiency: 60,000 × 0.80 = 48,000 BTU/h. The remaining 12,000 BTU/h is lost up the flue.

Question 40Heating Systems and Equipment

What is the standard remedy when a hot water boiler's relief valve weeps intermittently during firing?

  1. Increase the feed valve setpoint
  2. Install a higher-rated relief valve
  3. Verify system pressure and expansion tank operation before replacing the valve Correct answer.
  4. Cap the relief valve outlet

Explanation

Weeping usually means overpressure from a failed expansion tank or overfilling, so the cause must be corrected before condemning the valve. Increasing relief rating or capping the outlet defeats a safety device.

Question 41Heating Systems and Equipment

Which ignition method uses a silicon carbide element that glows to ignite the burners?

  1. Intermittent pilot
  2. Direct spark ignition
  3. Hot surface ignition Correct answer.
  4. Standing pilot

Explanation

Hot surface ignition uses a resistance element that heats to incandescence to light the gas. Spark and pilot methods use a flame or spark rather than a glowing element.

Question 42Heating Systems and Equipment

A technician observes that a furnace's temperature rise is 65°F while the nameplate specifies a range of 35°F to 65°F. What does this indicate?

  1. The blower is running at excessive speed
  2. The heat exchanger is oversized for the ductwork
  3. Airflow is at the low end and should be verified against static pressure Correct answer.
  4. The gas valve is overfiring the burners

Explanation

Temperature rise is inversely related to airflow; a rise at the top of the allowable range means airflow is near minimum. Excessive blower speed would lower the rise, and overfiring would be confirmed by manifold pressure, not rise alone.

Question 43Heating Systems and Equipment

In a two-pipe steam heating system, what is the role of the trap at each radiator?

  1. It balances water flow between supply and return
  2. It passes condensate while preventing steam from escaping Correct answer.
  3. It vents air from the radiator on startup only
  4. It regulates the steam supply pressure to the radiator

Explanation

A steam trap is a one-way device that lets condensate drain back while holding steam in the radiator. Air venting is handled by vents, and pressure regulation is done at the boiler or main.

Question 44Heating Systems and Equipment

Why must a condensing furnace be equipped with a condensate disposal system?

  1. The inducer motor requires water for cooling
  2. The gas valve produces water as a byproduct of regulation
  3. Combustion air contains dissolved moisture that must be drained
  4. Flue gas water vapor condenses as it is cooled in the secondary exchanger Correct answer.

Explanation

Cooling flue products below the dew point produces liquid condensate that is mildly acidic and must be drained, often through a neutralizing trap. The other components do not generate water.

Question 45Heating Systems and Equipment

A zone valve in a hot water system fails to open on a call for heat from its thermostat. Which test best isolates whether the valve or the control circuit is at fault?

  1. Check the boiler aquastat setpoint
  2. Measure voltage at the valve operator terminals while the thermostat calls Correct answer.
  3. Measure the circulator amp draw
  4. Verify the expansion tank charge pressure

Explanation

Presence or absence of control voltage at the valve terminals separates a wiring/thermostat problem from a failed operator. The other checks address unrelated system parameters.

Question 46Heating Systems and Equipment

Which statement correctly describes the sequence of operation in a modern induced-draft furnace with hot surface ignition?

  1. The igniter heats first, then the inducer starts and proves before the valve opens
  2. The valve opens, the igniter heats, and the inducer starts after flame is proven
  3. The blower starts first, then the inducer proves and the valve opens
  4. The inducer runs and proves, the igniter heats, the valve opens, and flame is proven Correct answer.

Explanation

The control verifies inducer operation with a pressure switch, energizes the igniter, opens the gas valve, and confirms flame before allowing the blower to start. Gas cannot be admitted before draft is proven.

Question 47Heating Systems and Equipment

A steam boiler is short-cycling and the sight glass shows the water level near the middle. The low-water cutoff is suspected. What is the appropriate verification?

  1. Raise the boiler pressuretrol setpoint
  2. Add water until the sight glass is full
  3. Increase the firing rate of the burner
  4. Blow down the low-water cutoff and confirm it interrupts the burner Correct answer.

Explanation

The low-water cutoff must be proven to stop combustion when the float drops, which is done by blowdown testing. Adjusting pressure or firing rate does not test the safety.

Question 48Heating Systems and Equipment

What is the primary purpose of a barometric draft regulator on a natural-draft gas furnace?

  1. It prevents backdraft by closing the flue when the burner is off
  2. It increases the draft by adding a powered blower
  3. It maintains a stable negative draft in the flue by admitting room air Correct answer.
  4. It measures the temperature of the flue gases

Explanation

A barometric damper swings open to admit room air and stabilize draft over a range of conditions. It does not measure temperature, seal the flue, or add powered draft.

Question 49Heating Systems and Equipment

A technician clocks a gas meter and finds the furnace uses 1 cubic foot in 30 seconds. If the local gas heating value is 1,000 BTU per cubic foot, what is the approximate input rate?

  1. 240,000 BTU/h
  2. 60,000 BTU/h
  3. 120,000 BTU/h Correct answer.
  4. 30,000 BTU/h

Explanation

One cubic foot in 30 seconds equals 2 cubic feet per minute, or 120 cubic feet per hour; at 1,000 BTU/ft³ that is 120,000 BTU/h. The math follows directly from the timed volume.

Question 50Heating Systems and Equipment

What does the AFUE rating of a furnace express?

  1. The airflow capacity in cubic feet per minute
  2. The annual fuel utilization efficiency over a heating season Correct answer.
  3. The maximum allowable flue gas temperature
  4. The steady-state combustion efficiency at full fire

Explanation

AFUE is a seasonal rating that accounts for cycling and standby losses as well as steady-state performance. Combustion efficiency and airflow are separate measurements.