NFI Exam Prep Guide – Verified Questions & Correct Answers for
Certification (Latest 2025/2026)
Combustion Requirements (3) - correct answerAir, Fuel, Heat
Complete Combustion Produces (4) - correct answerWater vapor, carbon dioxide, heat,
and non combustible ashes
incomplete combustion produces (3) - correct answercarbon monoxide, hydrocarbons,
and other gases
rate at which fuel burns is controlled by - correct answerthe amount of available air
air to fuel ratio is a - correct answercritical factor in obtaining optimum fuel combustion
BTU - correct answerBritish Thermal Unit, The amount of energy needed to heat one
pound of water one degree Fahrenheit
wood ignites at - correct answer450-550 F
natural gas ignites at - correct answer1,150 F
propane ignites at - correct answer920-1120 F
electric spark temp - correct answer1,700 F
hot surface igniter temp - correct answer2,400 F
butane lighter temp - correct answer3,200 F
stick match temp - correct answer3,000 F
cigarette temp - correct answer500-800 F
For complete combustion: air is ______ % oxygen + _____ % nitrogen - correct
answer20 : 80
for complete combustion, __(QTY)__ molecules of __(PART)___ need to be mixed with
___(QTY)__ molecule of _____(PART)____ in the presence of __(PART)__ - correct
answer2 oxygen : 1 fuel : heat
When complete combustion happens __(4 things)___ are released - correct
answerheat, carbon dioxide (C02), water vapor (H20), and nitrogen (N)
,Carbon monoxide is dangerous because (other than senseless) - correct answerit mixes
with blood and reduces oxygen carrying capacity
Aldehydes - correct answerchemical compounds that have a strong pungent odor
Carbon monoxide is ________ when aldehydes are present - correct answerpresent
Aldehydes result from - correct answerflame impingement and through the presence of
contaminated air
Efficiency formula - correct answerHeat output divided by heat input (percentage of heat
transferred to room)
3 Ts of efficiency - correct answerTemperature, turbulence, time
Temperature (efficiency) - correct answerminimum ignition temp
Turbulence (efficiency) - correct answerfuel must collide with oxygen molecules (refers
to the degree of fuel and air mixing that occurs in combustion zone)
Time (efficiency) - correct answeramount of time fuel gases remain in the high temp
zone. also known as "residence time"
Heat Transfer Efficiency - correct answerrefers to the percentage of heat generated by
combustion actually transferred to room
High heat transfer efficiency is normally associated with: (5 things) - correct
answerAppliance having proportionally large exterior surfaces with good heat radiating
properties
Long residence time of the hot gases in the Appliance
Adequate turbulence inside the appliance to property transfer heat from the fire
chamber to appliance walls
Rapid heat transfer through the walls of the appliance
Adequate air movement (convection) outside
2 types of factory built fireplaces - correct answerradiating and circulating
Radiant design - correct answertransmits heat energy from firebox opening by direct
radiation to the space in front of it. (do not have grills or louvers on the face, heat
moving blowers not avail.)
, circulating design - correct answeradds function of heat transfer via heated air
convection by circulating air around the fire chamber and releasing into space to be
heated through grills and louvers
Built-in, high efficiency fireplaces - correct answercontain efficient combustion and
convection champers that are enclosed in an insulated metal cabinet. Can be enclosed
in close proximity to combustibles
Fireplace inserts and hearth stoves are - correct answerdesigned to improve the
efficiency of an open fireplace and retain the general appearance of the fireplace while
improving its efficiency
Hearth appliance construction - correct answermodern solid fuel appliance designed to
introduce combustion air through specific and controllable air inlets and are controlled
by the user
Most controlled combustion devices are made of (metals) - correct answercast iron or
steel
Cast Iron (fireplace) - correct answermade from molds, can be decorative
Steel (fireplace) - correct answerwelded joints that need no service, some use steel
fireboxes inside decorative cast iron
Soapstone (fireplace) - correct answerlower thermal conductivity, delivers heat slowly
but retain and delivers heat longer
Conduction - correct answerdirect transmission of heat from one surface of solid
material to another surface of solid material
Convection - correct answertransfer of heat through a gas or liquid, including air, the
transfer of heated air between areas of unequal density. Natural occurs between
heavier, cooler air and lighter, warmer air
Forced convection occurs - correct answerBy mechanical means, aka electric blower
Radiation - correct answeremission of waves of infrared energy, converted to heat on
contact with solid surfaces
Radiant appliances - correct answersingle wall, exterior wall is firebox wall. Generally
required for large open spaces than small numerous rooms
Convection appliances (3 things) - correct answerdouble wall construction, allows room
air to circulate, convection currents, blower increases the amount and distance of
heated air circulation
Certification (Latest 2025/2026)
Combustion Requirements (3) - correct answerAir, Fuel, Heat
Complete Combustion Produces (4) - correct answerWater vapor, carbon dioxide, heat,
and non combustible ashes
incomplete combustion produces (3) - correct answercarbon monoxide, hydrocarbons,
and other gases
rate at which fuel burns is controlled by - correct answerthe amount of available air
air to fuel ratio is a - correct answercritical factor in obtaining optimum fuel combustion
BTU - correct answerBritish Thermal Unit, The amount of energy needed to heat one
pound of water one degree Fahrenheit
wood ignites at - correct answer450-550 F
natural gas ignites at - correct answer1,150 F
propane ignites at - correct answer920-1120 F
electric spark temp - correct answer1,700 F
hot surface igniter temp - correct answer2,400 F
butane lighter temp - correct answer3,200 F
stick match temp - correct answer3,000 F
cigarette temp - correct answer500-800 F
For complete combustion: air is ______ % oxygen + _____ % nitrogen - correct
answer20 : 80
for complete combustion, __(QTY)__ molecules of __(PART)___ need to be mixed with
___(QTY)__ molecule of _____(PART)____ in the presence of __(PART)__ - correct
answer2 oxygen : 1 fuel : heat
When complete combustion happens __(4 things)___ are released - correct
answerheat, carbon dioxide (C02), water vapor (H20), and nitrogen (N)
,Carbon monoxide is dangerous because (other than senseless) - correct answerit mixes
with blood and reduces oxygen carrying capacity
Aldehydes - correct answerchemical compounds that have a strong pungent odor
Carbon monoxide is ________ when aldehydes are present - correct answerpresent
Aldehydes result from - correct answerflame impingement and through the presence of
contaminated air
Efficiency formula - correct answerHeat output divided by heat input (percentage of heat
transferred to room)
3 Ts of efficiency - correct answerTemperature, turbulence, time
Temperature (efficiency) - correct answerminimum ignition temp
Turbulence (efficiency) - correct answerfuel must collide with oxygen molecules (refers
to the degree of fuel and air mixing that occurs in combustion zone)
Time (efficiency) - correct answeramount of time fuel gases remain in the high temp
zone. also known as "residence time"
Heat Transfer Efficiency - correct answerrefers to the percentage of heat generated by
combustion actually transferred to room
High heat transfer efficiency is normally associated with: (5 things) - correct
answerAppliance having proportionally large exterior surfaces with good heat radiating
properties
Long residence time of the hot gases in the Appliance
Adequate turbulence inside the appliance to property transfer heat from the fire
chamber to appliance walls
Rapid heat transfer through the walls of the appliance
Adequate air movement (convection) outside
2 types of factory built fireplaces - correct answerradiating and circulating
Radiant design - correct answertransmits heat energy from firebox opening by direct
radiation to the space in front of it. (do not have grills or louvers on the face, heat
moving blowers not avail.)
, circulating design - correct answeradds function of heat transfer via heated air
convection by circulating air around the fire chamber and releasing into space to be
heated through grills and louvers
Built-in, high efficiency fireplaces - correct answercontain efficient combustion and
convection champers that are enclosed in an insulated metal cabinet. Can be enclosed
in close proximity to combustibles
Fireplace inserts and hearth stoves are - correct answerdesigned to improve the
efficiency of an open fireplace and retain the general appearance of the fireplace while
improving its efficiency
Hearth appliance construction - correct answermodern solid fuel appliance designed to
introduce combustion air through specific and controllable air inlets and are controlled
by the user
Most controlled combustion devices are made of (metals) - correct answercast iron or
steel
Cast Iron (fireplace) - correct answermade from molds, can be decorative
Steel (fireplace) - correct answerwelded joints that need no service, some use steel
fireboxes inside decorative cast iron
Soapstone (fireplace) - correct answerlower thermal conductivity, delivers heat slowly
but retain and delivers heat longer
Conduction - correct answerdirect transmission of heat from one surface of solid
material to another surface of solid material
Convection - correct answertransfer of heat through a gas or liquid, including air, the
transfer of heated air between areas of unequal density. Natural occurs between
heavier, cooler air and lighter, warmer air
Forced convection occurs - correct answerBy mechanical means, aka electric blower
Radiation - correct answeremission of waves of infrared energy, converted to heat on
contact with solid surfaces
Radiant appliances - correct answersingle wall, exterior wall is firebox wall. Generally
required for large open spaces than small numerous rooms
Convection appliances (3 things) - correct answerdouble wall construction, allows room
air to circulate, convection currents, blower increases the amount and distance of
heated air circulation
