Basic Gas-Fired, Forced-Air Heating Systems Flashcards
Would you ever encounter a standard efficiency (65 - 75%) furnace in a new home?
No, in 1992 legislation was passed to ban furnaces lower than 78% efficiency. Old homes still have these.
What is the purpose of a thermocouple?
It shuts down the gas if there is no pilot flame.
Is a pilot safety switch 100% safe?
No, it will not shut down the pilot gas.
Why does propane pool on the ground?
Because it is a heavier gas than air and therefore does not rise.
What are three additional names for a safety gas valve (100% shutdown-[automatic pilot device])?
Thermomagnetic gas valve,
pilotstat,
safe-shut off valve.
How does a diaphragm valve operate?
By the use of a bleed port to allow a pressure difference on either side of the diaphragm, based on a small electrical input.
What is the most common Safety pilot device in use?
A combination gas valve.
Do belt driven fans require regular maintenance?
Yes their bearings and belts must be checked and greased if needed.
What are 4 thermocouple tests performed by an electrician?
Open circuit,
Closed circuit,
Response time,
Dropout point.
In a small furnace (<400000Btu/h) what is the maximum response time of a thermocouple?
3 minutes.
In a medium furnace (400000Btu/h to 1000000Btu/h) What is the maximum response time for a thermocouple?
20 seconds for propane and 90 seconds for natural gas.
If a closed circuit test reads a very small mV value, what is the likely cause of the problem?
A weak thermocouple.
Which thermocouple test is performed by a gasfitter?
Turn down test.
Thermocouples have a generally slow response time, why are they still so widely used?
Because they are simple, durable and inexpensive.
What is a typical thermostat setpoint for a Basic 24v FAH system?
20-25 degrees C.
