Module 2 Section 2 Gas Furnaces Flashcards
List 5 components of a gas furnace
fuel s system, system, combustion air delivery, burner assembly, heat exchanger, controls, venting system, distribution system
Purpose of the drip on gas piping:
To collect dirt & moisture, separating it from the gas before it gets to the gas valve.
One-half-inch diameter black steel piping should be supported every __feet, unless it is rising vertically, in which case it must be supported every __feet.
6 feet, and every floor
List 6 gas piping problems you should watch for
leaks, no drip leg, missing shut off valve, rusting, plastic pipe exposed above grade, improper connections
Incomplete combustion of natural gas produces:
a. nitrogen dioxide
b. carbon dioxide
c. ozone
d. carbon monoxide
e. sulfur dioxide
sulfur dioxide
Describe briefly how the pilot light & thermocouple work to ensure safety
pilot flame heats the thermocouple, which senses the flame, allowing the gas valve to open. If flame goes out, the gas valve is automatically closed.
The flame wavers over one burner in a gas furnace when the blower comes on. What is the likely cause?
a. heat exchanger failed
b. gas valve faulty
c. blower motor running too slow
d. airflow across heat exchanger is insufficient
e. vent partially blocked
heat exchanger failed
List 6 problems you’ll find on gas combustion equipment.
rust, scorching, inoperative, delayed ignition, short cycling, flame wavers, dirt or soot
What is meant by spillage & back drafting on a gas furnace?
spillage (back drafting) is when the combustion products flow out of the furnace into the room through the burner or draft hood, rather than up the vent. Life threatening situation
Using a mirror & flashlight to view the heat exchanger on a gas furnace allows you to see:
a. less than 20% of heat exchanger
b. 20-40% of heat exchanger
c. 40-60% of heat exchanger
d. 60-80% heat exchanger
e. all of heat exchanger
less than 20% of heat exchanger
Where possible, why should you watch the flame pattern of a gas furnace?
Look for changes in the flame pattern when the house air fan turns on. This indicates heat exchanger failure.
How many panel covers do most conventional gas furnaces have?
2- the blower compartment door, and the burner compartment door
List 6 problems commonly found with furnace cabinetry
rust, mechanical damage, missing components, inadequate combustible clearances, obstruced air intakes, scorching
List & describe the 3 settings on the fan/limit switch
Fan off-indicates the temp at which the house air fan stops (80 degrees to 110 degrees)
Fan on-indicates the temp at which the house air fan starts (120 degrees to 150 degrees)
High limit-indicates the temp which combustion is stopped for safety (170 degrees to 200 degrees)
List 6 problems commonly found with limit switches
set wrong or defective, scorching, rusting, mechanical damage, improperly wired, missing cover
List 6 problems you may find with a mechanical thermostat
poor location, not level, loose, dirty, damaged, poor adjustment/calibration
A heating thermostat located in a kitchen will tend to:
a. keep rest of house cooler than you want it
b. keep rest of house warmer than you want it
keep rest of house cooler than you want it
List 3 components of the venting system
draft hood, vent connector, vent
List 6 problems found with vent connectors
sections not secured together, rusted, poor support, poor slope, too long, too small/big furnace, inadequate combustible clearances
Should the smaller appliance vent connect into the chimney above or below the vent from the larger appliance?
a. Above
b. Below
above
If there is a chimney clean-out below the vent connection to the chimney, you should look up it to see ___ (2 points)
obstructions in chimney, connection between vent connector & chimney, if vent connector extends too far into chimney
The vent connector should slope:
a. downward going away from the furnace at a minimum of a quarter inch per foot
b. upward going away from the furnace at a minimum quarter inch per foot
c. downward going away from the furnace at a minimum half inch per foot
d. upward going away from the furnace at a minimum half inch per foot
e. not at all; should be horizontal
upward going away from the furnace at a minimum quarter inch per foot
We like to see vent connectors:
a. less than 3 feet long
b. less than 5 feet long
c. less than 8 feet long
d. less than10 feet long
e. length is not a concern
less than 5 feet long
A. What is the typical combustible clearance for a single wall vent?
B. What is the typical combustible clearance for a single B vent?
A. What is the typical combustible clearance for a single wall vent: 6 inch clearance
B. What is the typical combustible clearance for a single B vent: 1 inch clearance
List 6 common problems with furnace blowers
dirty, noisy, inoperative, overheating, rust, poorly secured
List 2 clues that the blower motor may be too small
excessive temp rise across the heat exchanger; poor airflow at remote registers
How much should a belt deflect when it is under proper tension?
a. 1/2”
b. 1”
c. 1 1/2”
d. 2”
e. 3”
1”
Do our standards require us to look at electronic air cleaners? Y/N
No
List 5 problems that could be found with mechanical filters in furnaces.
Missing, dirty, installed backwards, wrong size, loose or collapsed
Starting at the supply plenum, list the components of the duct system the air travels through to deliver heat to the room, & to re-enter the furnace at the return side.
The heated air is pushed through the supply plenum, along the supply ducts, out the registers into the room. The air travels across the room from supply register to return grille, through the return ducts to the return plenum, where it re-enters the furnace to be reheated.
List 3 things that cause friction loss in duct system
Duct size, elbows, high velocity, duct shape, length of duct
List 6 common problems with duct systems
disconnected, dirty, removed during renovations, leakage, rust, no air or weak air flow, registers obstructed
In a heating only climate, an uninsulated heating duct running through a garage will deliver__ air to the room at the end of the duct
a. warm
b. cool
cool
The vapor barrier on an insulated duct in a heating-only climates should be
a. on the side of the insulation closest to the duct
b. on the side of the insulation furthest away from duct
on the side of the insulation closest to the duct
Why is it unsafe to have a supply register supplying heat to a garage?
Exhaust fumes can enter the house when the furnace is not running
List 6 components that would be found inside the cabinet of a conventional gas-fired forced air furnace
gas valve, burners, heat exchanger, exhaust flue passages, draft hood, fan/limit, blower, air filter
The off-cycle losses of a conventional efficiency furnace total___% of the fuel consumed.
20%
List 8 common problems you may find with mid-or-high-efficiency furnaces
vent dampers stuck open/closed, ignition problems, condensate problems, induced draft fan problems, venting problems, differential pressure switch problem, spillage switch problem, poor outdoor combustion air intake location
It is impossible for a vent damper to fail in the closed position. T/F
False
List 5 reasons why an electronic ignition system may not work.
no electrical power, loose connections, poor electrical ground, no spark, flame sensor fails to detect flame, hot surface, hot surface ignitor cracked
Does condensate leakage out of the induced-draft fan housing cause corrosion problems with the primary heat exchanger? Y/N
No
List 5 problems commonly found with condensate systems.
blocked, leaking, poor discharge location, no neutralizer bath, clogged neutralizer
List 3 common induced-draft fan problems
damaged, worn bearings, inoperative
List 4 concerns with mid- or high-efficiency furnace vents.
Inappropriate materials, poor location for vent termination, mechanical damage, inadequate combustible clearance, improper slope
Do the standards require that we report on the life expectancy of furnaces? Y/N
No, although we have to advise our client if the system is near the end of its normal life expectancy
What is the typical life span for a conventional gas furnace?
a. 5 to 10 yrs
b. 10 to 15 yrs
c. 15 to 20 yrs
d. 20 to 25 yrs
e. 25 to 30 yrs
20 to 25 years
