Nate Gas Heat Flashcards
1
Q
Voltage to create spark ignition
A
15000
2
Q
Furnaces are placed into categories based on :
A
venting characteristics
3
Q
3 basic types of ignition
A
standing, direct and intermittent
on call for heat, 24 volt is applied to:
the gas valve in standing pilot the ignition module in intermittent the ignition module or Integrated Control Module in direct
4
Q
the intermittent ignition ignites
A
lights the pilot through spark igniters only on heat call and flame rectification. Applied AC voltage passes through flame in one direction thus providing DC voltage back to module via rectfication sensor.
24 volts powers ignition module
5
Q
direct ingnition systems
A
ingnite directly by hot surface igniter or spark and does not involve pilot.
6
Q
heat content in btus of 1 gallon of #2 fuel oil
A
137,000-140,000
7
Q
unconfined space
A
50 cubic feet or more per 1000 btus of input rating
8
Q
confined space needs a duct that is 1 square inch per_____ btus
A
5,000
9
Q
type of ingitiin system that uses a thermocouple
A
standing pilot
10
Q
blower in a furnace is usually started what kind of switch
A
temperature switch
11
Q
max supply gas pressure for most furnaces
A
14 wc
12
Q
electronic gas leak detector can give false leak reading by sniffing____.
A
pipe sealant
13
Q
to prevent condesation from getting onto heat exvhanger coil is installed____ of heat exchanger
A
downstream
14
Q
the common pipe the is join to the two category 1 vents shoulb be sized:
A
the size of the larger pipe plus 50% of smaller pipe.
15
Q
For complete combustion, burning 1 cubic foot of natural gas has _____ cubic feet of flue gas. In this 11 cubic ft includes 1 cubic ft of____ and 2 cubic ft of____ and 8cubic feet of _____ that doesnt take part in the burning of gas.
A
11 cubic feet, 1 of carbon dioxide, 2 of water vapor and 8 of nitrogen
16
Q
chiminey should be at least ___ ft above the peak of the roof
A
2 ft
17
Q
the problems of shortage or contaminated primary air are eliminated by _____ venting
A
direct
18
Q
true or false: a masonry chimney can be used to vent category 4 appliances?
A
false
19
Q
when does the pvc venting in a category 4 appliance require insulation?
A
when the legnth of pvc. exceeds the limits in the manufacter specs.
20
Q
to prevent flue gases from leaking a ____ must be installed
A
trap
21
Q
insulation is required on ductwork when it run in a _____ space
A
unconditioned space
22
Q
recommended merv rating on residential filters is
A
merv 8
23
Q
the disconnect of a furnace is generally located
A
on the side of the unit
24
Q
a standard gas valve has ___ coils
A
2
25
the part of the thermostat that contains the functioning switches is the
subbase
26
in 1992 rhe us department of energy only allowed units with at least an AFUE of ___% to be installed
78%
27
many pre 1992 furnaces AFUE are around ___%
60%
28
under ideal conditions, ignition tempratures for natural gas is ______ degrees and burns at ______degrees
1100, 3500
29
propane and butane are both ____ than air.
heavier than air
lp gas 1.52 times heavier than air natural gas is 0.6 times lighter than air
30
residential furnaces have blowers that range from __ to ___ horse power.
1/4 to 1/2 horse power.
31
carry over channels or " crossover channels" pass flame from first burner to the rest of the burners
crossover channels
32
purpose of combustion blower is not to vent flue gas but to
provide combustion air.
33
Natural gas consist of what blend of gases?
90% methane and small amounts of propane to balance the btu content of the gas.
34
LP gas is what blend of gases?
propane and butane added to balance the btu content.
35
3 types af gas use in furnaces are
natural, LP and manufactered
36
___ cubic feet of primary air is required for 1 cubic foot of LP gas for complete combustion.
1 cubic foot of LP gas has ____ btu content.
Manifold pressure needs to be set at___ WC
24 cubic feet
2500btu content of lp
11 in wc
37
larger commercial building may need 2 or 5 psig of ____ and needs a second ____ to reduce pressure to the units
gas, regulator
38
gas is provided to residential homes at__ psig or 14 inches in wc
0.5 psig
39
In converting a furnace to LP gas, the oriface is ______ for the pilot and manifold due to the high btu content and the higher pressure gas helps with introducing more primary air. The gas ____ may need to be changed or adjusted.
smallar, regulator
40
combustion is a ______ reaction
chemical
| - the hydrocarbons in the fuel unite with the oxygen when heated to ignition temperature.
41
the fuels for combustion are varing amounts of _____ and ______.
hydrogen and carbon.
42
the by products of combustion are ____,______ and _____.
carbon dioxide, water vapor and heat.
43
CH4 is ______.
methane
44
incomplete combustion has the byproducts _____, ______ and _______.
carbon monoxide, soot, and others
45
for a confined space, (utility closet) openings for air coming from outside structure should be neaer the floor and ceiling should be made.
1 square inch per 4000 btus
46
air from inside a building for a confined space ( utility closet ) should be provided by 2 openings. 1 12 inches from the ceiling and 1 12 inches from the floor.
1square inch per 1000 btus
47
combustion air can be contaminated with what?
chemicals, dust, bleach, dyes, paint fumes, hair spray, dryer lint.
48
What can cause incomplete combustion
low amount of combustion air.
49
only areas that have fully louvered doors or no doors can be considered as an________.
unconfined space
50
wood louvers have a free area of_____
20%-25%
51
metal louvered doors or grills have a free area of_____.
60%-70%
52
primary air in an induced draft furnace is controlled by________ and _______.
gas pressures and the induced draft fan.
53
primary air in an atmospheric burner is controlled by ______
air shutters
54
what fluid does the dumbell co2 tester contain?
| it is good for_____ samples
potassium hydroxide which absorbs co2
| 250
55
if co2 reading is low it is an indication of_____ or that the _______.
too much excess air or fuel isnt burning completely.
56
what types of air shutter are there for atmospheric furnaces?
butterfly
wing
and disk
57
What needs to be maintained in a digital combustion anylizer
the sensers and they have a limited lifetime.
58
What is the first stepnin combustion analization?
checking manifold pressure.
59
Combustion Efficency
the percentage of useful heat of the total heat being produced by the burning gas.
60
2 Measurements that establish combustion efficiency.
co2 and net temprature of flue gas
Measurements taken in same hole at the inlet of draft hood.
61
the object of efficiency testing is
obtain all the heat possible from the potential amount of gas without creating undesirable conditions.
by : overall combustion performance
burner performance
heat exchanger operation.
62
how do the thermocouple operate
provides proof that the flame is present and in the presence of heat the thermocouple produces 18- 30 milivolts which holds open pilot valve.
As long as flame is present gas flows from pilot valve to pilot burner and the secondary/ main valve.
63
mecury flame sensor is installed where
in older systems on the gas valve.
64
What valve is uses in typical Furnaces today
Combination gas valve. It posesses
2 separate gas valves (Standing ignition systems: main gas operated by 24ac volt signal from thermostat and pilot gas 18-30minivolt signal from thermocouple/ In intermittent ignition systems both valves are controlled by 24v signal from thermostat.)
Manual shutoff
pressure regulator
( 2 stage valve includes a second regulator where the 1st stage uses close to half the pressure of the 2nd stage.)
65
Furnace is sized for unit input btus or output btus
output
66
In basement installation what must the installer consider?
location of:
fuel lines, combustion air, venting, condensate lines and duct runs ( ducts must not touch the ground to prevent moisture infiltration.
concrete base is non combustible and is ok to use as base.
67
In crawl space installation, what must the installer consider?
where to hang unit from floor joists,
Ducts must maintain minimum clearance from ground to prevent moisture infiltration.
Ducts must be insulated and coverd in vapor barrier.
68
in attic installation what must the installer consider?
Units are frequently hung from roof rafters or sits on ceiling joists
It is critical for the load to be evenly spread among the trusses.
A base larger than unit
non combustible floor for downflow and zero side.
69
what is the installer to consider for a closet install?
down flow needs non combustible floor.
70
for garage install what is the installer to consider
furnace must be mounted off the floor to reduce risk of igniting gas fumes that settle on the floor.
Distance can vary how far off the floor. Check with authority having jurisdiction. (AHJ)
Ducts withing the garage must be sealed within garage space to prevent fumes from entering duct system and being carried into the house.
There may be requirements for firedampers for duct work passing through garage wall into house.
71
pipe for natural gas material is what.
threaded steel pipe or CSST corrugated stainlesa steel.
chemicals with some gas supplies can damage copper.
72
what is the purpose of sediment trap
it catches and prevents moisture, oil and particles from contaminating the gas valve.
73
what is the purpose of a union
for easy disassembly of gas piping between sediment trap and gas valve for service.
74
will refrigerant leak detectors detect a gas leak
no. an electron gas leak detector is sensitve to gas levels as 20ppm to 50ppm which gets louder or faster as concentrations increase.
Pipe dope gives off solvents that give false reading.
ultrasonic leak detectors and soap bubbles can be used.
75
condensate piping for high efficiency furnaces should be:
minimum 1/8" per foot pitch
air conditioner and furnace can share same condensate line but both have there own traps.
And lines should be open vented.
Never pipe drain line to sewer. it could back up into furnace.
condensation should be first dry fitted than glued and than turned slightly at connections to ensure proper sealing.
76
If furnace ia installed with heatpump what terminal would the furnace be wired to?
W2/ second stage.Additional controls are required to keep heat pump and furnace running at the same time.
Heat pump will shut down while fau is running. when tempratue is satisfied, the fau cools and than the heat pump comes back on.
77
What factors must be considered when Selecting the size of a humidifier for a home.
-cubic feet of conditioned space
-outside temp
-desired relative humidity
( if relative humidity is too high for outside temp condensation will form on cold surfaces such as windows.)
78
What type of humidifiers are available and what are the most common?
-Bypass( pressure difference between the supply and return cause the warm supply air to go through the wetted pad in humidifier and into return duct. A manual damper is generally used and must be shut during cooling season.
-fan powered( has its own fan which draw air from the duct and pushes it back into the same duct.)
-steam ( generates steam and injects it into the supply air stream.)
- atomization (generate a fine mist of droplets and injects by a nozzle into the return air stream.)
the most common are the bypass and fan powered
79
When installing zone system, what component is needed?
a bypass damper
- motorized damper
- barometric damper ( allows airflow to pass when system static pressure exceeds certain point.)
80
What Standard are Zone Air distribution systems to be installed by?
ACCA/ANSI
81
What precautions are there to consider when using the bypass damper method in a zone system?
1. Installing the duct from the supply side to the return side as FAR AWAY from equipment as possible.
2. In heat mode the control board can fail and the heat exchanger can over heat and have a short cycling of limit switch.
3. In cooling the coil can freeze due to the air being to cold from the return side and would cause premature compressor failure.
82
Whats a good alternative to a bypass damper method.
The dump damper method.
Dumps air to a basement,crawl space, unoccupied area of the home.
Barometric damper is installed and adusted to open when the smallest zone(s) are calling.
83
psc motor wire colors and what is the C/N, Start winding and Run winding.
Neutral: White
Run Winding: Red, Black
Start Winding: Brown or Purple ( capacitors)
84
What readings will you have if the psc motor has a tripped intenal overload?
Start to Common: Open
Run to Common: Open
Start to Run: Resistance Reading.
85
What does a run Capactor do to sngle phase motor
causes a second phase ( or phase shift )that produces a rotating magnetic field.
86
How to ohm test capacitor
jumps to zero and rises. up gradually to infinity.
87
what side is zero on and the infinity on an ohm meter.
0 is on the right and infinity is on the left
88
what scale on ohm meter do you read start capacitors
Rx100 or R× 1,000
89
what scale do you read run cap in
1000 to 10,000
90
What steps are to be taken when troubleshooting a control board?
1. Voltage input
2. Fuse
3. Voltage outputs
4. Visual Inspection.
91
What does a spill switch do in a furnace?
Shut off gas supply if flue gases escape from flue or chimny.
92
what does a blower switch do in a down flow furnace.
it shuts off furnace if the blower compartment becomes to warm before the dan comes on.
93
Category 1 Appliance
non positive static pressure with stack temprature that avoids excessive condensation.
94
Category 4 appliance
a positive vent static pressure with a stack temprature that can cause excessive condensation.
95
What are the 2 factors that impact the driving force of venting.
1. The density of the hot gases ( depends on the average temprature of the gases)
2. The height of the vent pipe.
The hotter the gases and higher the vent, the greater the driving force through vent.
96
For atmospheric/gravity venting, what can wind do to alter venting force
wind blowing into vent can cause restriction to flow from vent. ( down draft/back draft)
wind blowing by terminal (exhaust) can cause a negative press in vent cause updraft.
97
What is the exception to updraft and down drafting in a venting system?
A sealed combustion appliance where the air inlet and exhaust are installed as close as possible to each other so they are operating of the same pressure plane. Because the vents are balaced, working off the same pressure, it cancels out the up and down drafting.
98
What is used in vented appliances to overcome wind effects?
Draft hood or draft diverter.
99
What does a draft hood consist of?
1. Inlet opening (connected to flue outlet )
2. Outlet opening (connected to vent pipe)
3. Atmospheric opening ( installed above burner level.
100
4 common types of draft hoods
vertical to vertical
vertical to horizontal
horizontal to horizontal
horizontal to vertical
101
Updraft conditions cause:
more cool dilution air to go through draft hood atmospheric opening than combustion air to go through the burners. This cause lower stack tempratures due to cooler air going up through the vent at atmospheric opening.
102
Down draft conditions causes:
flue gas to still burn with atmospheric pressure at flue outletand temporarily spill out of atmospheric opening instead of venting out of exhaust due to positive pressure from wind.
103
When should direct venting be considered?
- If environment can go into negative pressure from exhaust fans
- if there is significant amounts of dust,lint,or chemicals that can be drawn into combustion chamber which can cause premature heat exchanger failure.
104
What material Approved by the NFGC (national fuel gas code) is used for Category 4 appliances.
Approved PVC for most manufacters and stainless steel which will hold up to the corrosive condensate for a few manufacters.
105
venting for category 4 furnace is under _____pressure so the fittings must be____ to prevent any flue leakage.
positive, sealed.
106
What fitting is used for category 4 venting to allow exhaust and combustion air in the same piping?
concentric Y fitting. Flue gas on the inside pipe. Combustion air on outside pipe.
107
What will a oversized pipe do and an undersized pupe cause?
Undersized vent connector creates too much restriction and will have an improper amount of air moved by the induced draft fan.
Oversized will cause a greater amount of condensate to form and slows the velocity down.
108
how far above expectex snow level is the vent pipe to be terminated
12"
109
Venting according to NFPA 54/58 for category 1 appliances
-vent connector diameter the same as unit flue connection.
-the vent shall run with as little turns as possible.
-upwards slope of 1/4" per ft.
-vent connector cannot go beyond the wall but through the wall
-connector must be supported and cant run into an open fireplace chimny.
- vent needs weather hood.
- must be at least 3 ft through roof and 2ft above peak with ten ft horizontal plane.( prevents down drafting)
- venting ran through walls and roofs must meet requirement for combustion materials.
-
110
When heater capacity is in question, how do you test furnace venting if join to water heater?
turn off water heater and temporarily block off water heater vent.
111
Type of vent that provides an insulation to prevent condensation
bvent
112
What is the formula for calculating air flow in a furnace
cfm = output btus/ 1.08 × temprature rise.
113
Positions of Fau
horizontal, vertical, downflow, lowboy.
multipositional handles all positions.
114
How many combustion air and drain lines come with a high efficiency furnace.
2 combustion air and 2 drain lines.
| - plugs are applied to lines not in use.
115
what limit switch is manufactured in a counterflow system
auxilary limit on blower housing.
| -it moniters return air and interrupts burner if the return air is to hot.
116
LP gas is boiling point at atmospheric pressure is ____ which makes it feasible to store in tank at low temo climates.
- 44 degrees
117
Why does LP gas have more btu output than natural gas?
Lp has more atoms of hydrogen.
118
what is the btu output of butane?
3200 btu per cubic feet
119
What is mixed with propane and butane to lower the btu output in order to closely duplicate gas?
air.
120
common manifold pressure for gases are:
Natural gas and propane/air gas mixture: 3.5 wc
Manufactured gas (below 800 btu): 2.5 wc
L2:LP gas. 11 wc
121
What is another term for combustion
rapid oxidation.
122
If flame burns yellow, tech should suspect
low combustion air.
123
What mixture of air and gas will burn and wil not burn?
0%-4% will not burn, 4%-15% will burn.
124
what determines ignition/flame velocity?
the hydrogen content of the type of gas and air -to-gas mixture.
natural gas burns slower than butane because natural gas has 4 hydrogen atoms and butane has 10.
125
Perfect combustion requires____ parts oxygen and _____parts methane.
2 oxygen, 1 methane.
126
What percentage 1 cubic ft of the air is oxygen
close to 21%
127
Typical combustion take ____ part oxygen and ____ part gas
3 oxygen, 1 gas
128
The gas regulator _____ the pressure for a constant manifold pressure.
decreases
129
Gas regulator ____ clockwise and _____ counter clockwise.
increases, decreases
130
Lp gas regulators are furnished at the ______ and regulates the pressure to____wc
supply tank, 11
131
The gas solenoid is a ____ switch
NC
132
What types of valves within a gas valve are available?
solenoid, diaphragm, heater controlled.
133
Types of Automatic Combination Valves
- Standing Pilot (with flame proven and power unit open: both pilot first and second automatic valve open simultaneously with signal from thermostat )
- Intermitten pilot. (Control module opens first automatic valve, flame is proven through flame rectification, (90 sec per attempt to relight pilot) than control module opens second automatic valve opens
- Direct burner ( control module opens primary and secondary valve simultaneously, shuts off if no flame is proven between 4 to 12 seconds)
134
What is a Redundant valve?
- has 2 or 3 valve operators in series physically
| and wired in parallel.
135
Inshot burners are made of __________ that has ________ to each main burner for good flame rerention and proper flame carry over.
aluminized steel, crossover.
136
all burners are know as ________ burners
atmospheric
137
heat exchangers are made of ___________ or _________.
sheet steel or aluminized steel.
138
burners are normally located on the _______ of the heat exchanger. High efficiency FAU burners are located on the ____ of the heat exchanger in a _____ chamber for the purpose of condesation produced flowing downwards in accordance with gravity.
bottom, top, sealed
139
inshot burners have no ________ adjustments.
primary or secondary air.
140
What type of burners are in Fau's
- cast iron with slotted ports
- stamped steel slotted burner
- ribbon burner
- up shot
- inshot
141
if too much air flows across heat exchanger, the flue gas will become __________ and the products of combustion may ______ and run down the flue pipe.
too cool, condense
142
if there is an insufficient amount of airflow across the heat exchanger, the ________ will over heat and cause stress on heat exchanger.
combustion
143
when temprature rise on the decreases as efficiency ________
increases.
144
heat output is also added by the _____
blower motor
145
Poor combustion can .....
- corrode a heat exchanger.( H.E. may be coated or bonded with aluminum, glass or ceramic material which are more corrosive resistant and assit unit in lasting longer.) stainless steel resists corrosion extremely well.
- insulate the heat exchanger
146
The heat exchanger in modern furnaces is made of
L and S shaped aluminized steel tubes with a stainless steel transition box in between the 2 tubes. the transition box may accumulate condensation and is designed for that potential.
147
What typ of fan switches can be found?
| The can be ______ or _______ or combination of both.
- Bi metal helix ( temp on temp off) adjustable
- bimetal strip resistance heater (time on temprature off) adjustable
- bimetal strip that is not influenced by the heat exchanger. (time on and time off) non adjustable
- dip switches adjustable for off delay
148
DIP is an acronym for...
Digital Inline Pair
149
The fan will always come on within ____ of ignition and is not adjustable
30 seconds
150
What Coating is on the secondary heat exchanger?
plastic polypropylene
151
States have different high limit cutt outs which range between _____ and _____ degrees
200 to 250
152
The combination fan switch/high limt control is a _______ and operates off the ____ switch(s).
They can be low voltage , high voltage or a combination of both and can be retrofitted.
bimetal helical, same
153
If combination fan/high limit switch is used, and it needs to be wire for high voltage, the jumper wire must be _____. If the limit switch is to be low voltage and the fan high voltage the jumper must be______.
used, removed.
154
In an aerated pilot air is mixed with the gas ____ it enters the pilot burner.
before
155
in a non aerated pilot it only uses __________ at the point of combustion.
- dust needs removed in maintenances
secondary air
156
For standing Pilots there are 3 types of flame proving devices called:
- thermocouple/thermopile : to dissimilar metals welded together (hot junction) wires/metals split at the bottom of thermocouple (cold junction) lead to the load (power unit) to complete circuit when heated. If flame goes out, thermocouple will cool of btween 30 - 120 seconds.
- bimetallic safety device: the bimetal warps and closes its contacts and keeps power unit energized.If flame goes out, metal cools and opens its contacts close to 30 sec.
- liquid filled remote bulb: as the mercury in the bulb expands as its heat by the pilot burner, the diaphragm expands and connects its contacts in gas saftey valve.
-
157
For condensing furnaces between 40,000 and 75,000 btus the venting should be a minimum of ____ in diameter is used. For units between 90,000 and 120,000 a ____ is used.
2", 3"
158
What is the minimum height of the drain vent?
5" high
159
what is the max separation between combustion and exhaust
3"
160
What 4 parameters determine furnace efficiency ratings?
- type of draft
- Amount of excess air used in combustion chamber
- delta t
- flue stack temperature
161
Stack temprature for Conventional furnace
- 415 - 525 degrees
- 70-100 delta t
- 40- 50% excess air
162
stack temprature for mid efficiency
- 302-402 degrees
- 45-75 delta t
- 20-30% excess air
163
High efficiency furnace delta t
-100-140
-35-65 delta t
10% excess air
164
The higher the AFUE the more ______ the combustion equipment is at converting fuel to useful heat energy.
Example: an 85 percent furnace is used for useful energy and 15% is wasted.
efficiently
165
A 100% shutt off system
when there is a failure to prove flame and both the pilot valve and main gas valve shut down.
166
A non 100% shut off
the pilot valve continues to bleed gas after a failure in proving flame and the main valve shuts down. ( used on roof top units)
167
continuous retry with 100% shut off.
shuts main gas valve and pilot valve and flame is not proven and will not bleed gas but will retry in 90 seconds.
168
What is lock out
after lighting and attempted relighting the system will go into a soft lockout ( 5 min to an hour) and than keep attempting after that period. It can possibly go into hard lockout after several soft lockouts which would require a manual reset.
169
Purpose of pre purge in combustion fan
to rid heat exchanger of unwanted flue gases, fumes, or dust that may have accumulated during last heating cycle.
170
purpose of interpurge for combustion blower
to rid of risidual gas. or combustion byproducts from previous unsuccessful ignition.
171
purpose of post purge for combestion motor
double insurance that the heating cycle will start with only air in the heat exchanger.
172
Flame rectification is the safest and fastest and most reliable method for proving flame. It changes ________ current into direct current.
alternating current
173
For intermittent pilot to work, the spark needs a ______and a high quality arch to ingnite flame.
The spark sparks ____to____ times per minute.
ground to earth ( a ground strap near pilot assembly or pilot hood.)
60-100
174
Direct spark ignition compenets are
igniter, sensor, and dsi module. The sensor proves flame that igniter has fired and sends microamp signal to dsi module. Spark ignition the igniter is also the flame senser.
ignition trial is for 4- 11 seconds.
175
most ignition problems are related to
spark gap, igniter positioning, and bad grounding.
176
If sparking doesnt stop sparking after ignition what could be the issue.
the ignition module.
177
What material is a Hot surface igniter and what voltages does it work off of?
silicon carbide
120 for hot surface igniter
excess voltage above 125 will shorten the life of device.
and 24 volts to a pilot.
178
how should a spark igniter be positioned in a direct spark ignition system
.16" spark gap between igniter and ground strap.
- spark gap to be centered above the left burner port
- 7/16" above the burner port
179
how does flame rectification work
2 electrodes that have ac voltage supplied to them from the module and the flame acts as a switch where the eletrons produced by the gases move at various faster sleeds than the 100,000 times heavier ions, towards the electrode of least resistance back to the sensing circuit only as a pulsating dc circuit to prove flame to the module.
180
What are the electrodes in each ignition system?
| Which are also known as dual rod or remote sensing systems.
intermittent: the pilot hood and grounding strap(ground to earth) and the flame senser or flame sensor.
the jumper would be cut on most modules.
Direct ignition: the main burners ( earth to ground) and flame rod or sensor.
181
what is known as a single rod or local sensing system?
When ignition and sensing are accomplished through the same large ignition wire. The jump would be needed control module.
182
how many dc micro amps can be produced in flame rectification
1-25
0.000001 - 0.000025
183
How is dc micro amps measured
```
in series with a microammeter
between the burner ground terminal of ifc or module to the burner.
```
184
what is the minimum resistance of a gas valve
20 ohms
185
under load what is a bad thermocouple
9 dc millivolts
186
The actions of CO and O in combustion analysis indicate either a _______ issue or a ______ issue.
The amount of CO2 indicates Combustion Efficiency ( Heat input minus stack loss)
as O increases CO2 _____. As O decreases CO2 ______
draft, combustion air.
| Decreases, Increases.
