Furnaces
List the four categories of gas fired furnaces based on flue gas temperature and pressure
Category I, Category II, Category III, and Category IV
What is the purpose of the orifice located on the gas manifold?
The orifice meters the gas into the burner.
What is the difference between a a 90 percent furnace with a sealed combustion system and a typical 90 percent furnace?
Sealed combustion units require combustion air to be piped in from the outsid
Explain the difference between a Category I furnace and a Category IV furnace?
A Category I furnace operates with a high temperature, negative pressure vent. A Category IV operates with a low temperature, positive pressure vent.
Why is it not a good idea to drill out orifices in the field?
The hole must be drilled precisely. Errors can result in dangerous burner malfunctions
A Category I furnace operates with a
High-temperature, negative-pressure vent.
List the five furnace cabinet configurations.
Up-flow, down-flow, horizontal, low boy, multi-position
What is the purpose of the burner venturi?
The shape of the venturi causes the gas and air to swirl as they pass through the constricted opening, mixing them together
How does air flow in a standing-pilot, natural-draft system
It relies on heat to increase the buoyancy of the air to pull air into the combustion chamber and force flue gases into the proper vent
What changes were made in furnace design to achieve 80% efficiency?
Removed standing pilot light, flatten and serpentine heat exchangers, and added induced draft blower.
What may happen if the gas stream through the in-shot burner does not pass straight inward and hits the side of the venturi?
This causes poor ignition and even explosions
A stainless steel coil that is built like a refrigeration coil and allows a high-efficiency unit to move into the 90+ percent efficiency range is called:
A recuperative coil
What is the difference between an 80% efficient furnace and a 90% efficient furnace?
90% furnaces have an extra recuperative heat exchanger that condenses water out of the flue gas.
What factors determine the size of a burner orifice?
The size of the orifice is determined by three factors: the specific gravity of the gas, the heat content of the gas, and the required BTU/hr rating of the burner.
What precautions should be taken when using an unvented gas heater?
The primary concern for unvented space heaters is the oxygen depletion and possible carbon monoxide buildup.