in a modern gas furnace, the component that separates the combustion gases from the supply air is the __________.
gas valve
heat exchanger
inducer fan
plenum box
what type of furnace moves warm air through the conditioned space without a fan?
gravity
horizontal
lowboy
upflow
furnace heat exchangers generally are made of ___________.
ceramic
copper
plastic
steel
what does AFUE stand for?
actual fuel usage efficiency
annual fuel utilization efficiency
annual furnace usage equivalency
approved fuel usage estimate
the main purpose of a secondary heat exchanger is to _________.
evaporate the flue gases
provide a backup containment
remove additional heat from the flue gases
reverse the primary air flow
which gas commonly used as a fuel in gas furnaces is heavier than air?
butane
isobutene
methane
propane
which grade of fuel oil is commonly used in residential furnaces
1
2
3
4
how many cubic feet of air are needed to burn 1 ft3 of natural gas
6
10
18
24
how many cubic feet of air are needed to burn 1 ft3 of propane
what is the approximate heat content of 1 ft3 of natural gas?
500 btu
800 btu
1050 btu
2500 btu
what is the approximate heat content of 1 ft3 of propane
what is the approximate heat content of one gallon of No.2 fuel oil?
75,000 to 90,000 btu
95,000 to 135,000 btu
137,000 to 142,000 btu
145,000 to 170,000 btu
what is a typical manifold pressure for a natural gas furnace?
3.5 in w.c.
11 in w.c.
2 psi
5 psi
what is the typical atmospheric manifold pressure for a propane furnace?
what type of furnace is commonly installed in a closet with underfloor supply ducts?
downflow
which of the following is required for combustion?
fuel
heat
oxygen
all of the above
which of the following is not a product of complete combustion?
carbon dioxide
carbon monoxide
water
an unconfined space (in terms of furnace installation) is defined as a space with a volume equal to or greater than _______ per 1,000 btu of input rating
25 ft3
50 ft3
75 ft3
100 ft3
combustion air may be added to a confined space by a duct to the outside, sized on an input of 1 in2 per __________.
1000 btu
2000 btu
4000 btu
5000 btu
what type of burners are commonly used with induced-draft gas furnaces?
gun style
pot style
ribbon
inshot
what is the typical color of a properly burning gas flame?
blue
orange
red
yellow
in a gas furnace, primary combustion air is introduced in the ________.
burner prior to ignition
burner after ignition
gas line
a "dumbbell" style CO2 tester ___________.
contains a test fluid that absorbs CO2
measures CO2 in parts per million
provides a digital readout
requires a power supply
useful heat output, expressed as a percentage of the total burner input, is known as the ________ of a gas furnace.
combustion efficiency
fuel efficiency
heat exchanger performance factor
heating coerfficient
which type of ignition system uses a thermocouple?
direct ignition
hot surface
intermittent ignition
standing pilot
the blower in a standing pilot furnace is generally started by a(n) __________.
differential pressure switch
ignition module
temperature switch
time-delay relay
a furnace with an induced draft fan uses a ________. to prove air flow
high pressure switch
lower pressure switch
pressure differential switch
sail switch
flame rectification proves flame by creating a signal in response to a ________.
change in resistance
current conducted in one direction through the flame
temperature activated switch
voltage produced by the flame
when the output of a furnace matches the heat loss or heat gain of the conditioned space, the system is said to be at its
balanced point
design temperature
full-load condition
reference point
residential load calculations should be completed according to ACCA's
manual D
Manual J
Manual N
Manual P
when furnaces are installed in attics or crawl spaces, special care must be taken to__________.
distribute weight properly
insulate the ductwork
protect water lines from freezing
which of the following is true of low voltage control wiring.
it is exempt from NEC requirments
it may not be run in the same conduit as line voltage
it may not exceed 100ft in length
it must be ran in metal conduit
what is the maximum pressure that can be supplied to most natural gas furnaces?
3.5 in W.C.
14 in W.C.
the sensor of an electronic leak detector can be affected by ________. which may cause the instrument to give a false indication of a gas leak
cutting oil
moisture
pipe sealant
teflon tape
what is the minimum diameter for condensate drain pipe
1/2 in
3/4 in
1 in
1 1/4 in
generally speaking a residential thermostat should be mounted _________.
approximately 5 ft off the floor
in the kitchen
near a supply register
on an exterior wall
which is the proper terminal for heating on most thermostats
C
G
W
Y
B
H
on an auto changeover thermostat, the difference between heating and cooling setpoints (that keeps the equipment cycling back and forth between heating and cooling) is know as the ________.
deadband
droop
offset
throttling range
in order to prevent condensation from forming in the heat exchanger, the cooling coil should always be mounted ________.
from behind :-)
before the heat exchanger
below the heat exchanger
downstream from the heat exchanger
upstream from the heat exchanger
in the summer months, the damper on the bypass humidifier should be _________.
fully closed
fully open
partially open
removed
which of the following is NOT true of a residential zoned system
each zone has its own temperature control
there can be no more then four zones
zoned units may use a by pass damper to pass excess supply air back into return air
zoned units may use a dump damper to pass excess supply air to a non-critical area
a type of equipment that transfers both latent and sensible heat from the exhaust air to the supply air is know as a(n) ________.
economizer
energy recovery ventilator
fresh air intake
heat recovery ventilator
a standing pilot furnace with an atmospheric burner is an example of a __________ gas appliance
category I
category II
category III
category IV
a high efficiency condensing furnace is an example of a _________ gas appliance
Category III
burning of 1 ft3 of natural gas produces __________ of flue gas
1 ft3
2 ft3
10 ft3
11 ft3
which of the following affects the venting force in a gravity venting system
the height of the chimney
the percentage of CO2 in the flue gas
the type of fuel used
the type of fuel pipe used
a fan is used to pull flue gases through the combustion chamber in a(n) _________ vent system.
forced draft
induced draft
natural draft
how far above the peak of the roof should the chimney extend
1 ft
2 ft
3 ft
4 ft
a horizontal flue vent must have an upward slope of at least _________ per foot of length.
1/8 in
1/4 in
problems related to a shortage or contamination of combustion air are eliminated in a(n) vent system
direct
when can a masonry chimney be used to vent category IV appliances?
when it is existing chimney
when it is no more that one story tall
when it is used as a common vent along with a category I appliance
Never
category IV furnaces are commonly vented with what type of material
single wall metal
double wall class B
masonry
PVC pine
when does a category IV vent pipe require insulation?
always
never
only when the vent pipe runs outdoors
when the length of the vent pipe running through an unconditioned space exceeds the length listed in the manufacturers tables.
category IV equipment required a condensate drain. a trap must be installed in the drain line to _________.
break the vacuum allowing water to drain
keep water from draining to quickly
prevent water from freezing
provide a seal that prevents the leakage of flue gas
