HVAC CH51

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.

What components are needed for a furnace to operate as a two-stage furnace?

-A two stage gas valve -two draft proving switches -two speed induced draftfan -two stage thermostat.

What changes were made in furnace design to achieve 80 percent efficiency

-removal of the pilot light -improvement of the heat exchanger -the addition of an induced-draft blower

Horizontal Furnace

*Installed in low areas such as crawl spaces, attics, or basments

Counterflow/Downflow Furnace

*are widely used where duct systems are set in concrete or in a crawlspace beneath the floor *A fireproof base is required when the furnace is installed on a combustible floor *An extra safety limit control in the fan compartment is required.

Lowboy furnace

*built low in height to accommodate low ceilings *air goes in the top of the furnace, makes a 180° turn as it goes through the furnace, and then leaves out the top of the furnace. *Many of these furnaces are sold for retrofitting older homes.

Multipositional Furnace

*can e configured to a upflow, horizontal, and/or downflow furnace

Upflow Furnace

*upflow of air *Most Popular *

Direction of Air Travel in a furnace

*upflow-up *downflow/counterflow-down *horizontal flow-horizontal

Why are some condensate pumps not approved for furnace condensate?

The condensate from a furnace is mildly acidic and can damage thematerials in some condensate pumps.

What is the temperature rise of a furnace?

The difference between the air entering the furnace and leaving the furnace

Why are draft-inducer fans necessary in today's furnaces?

The flue gasses cannot make their way through the new heat exchangers on their own.

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 burnermalfunctions.

What is the purpose of the orifice?

The orifice meters the gas into the burner

What part of the furnace does the air travel through first in all furnace cabinet configurations?

The return air enters at the fan housing end of the furnace and travels to theheat exchanger end.

Why should technicians be familiar with standing-pilot, natural-draft furnaces, since they are no longer manufactured?

There are still many standing pilot natural draft furnaces and appliances inuse.

Why do most furnaces today use burners?

They are more efficient and they fit today's narrow heat exchangers better.

Why are standing-pilot natural-draft furnaces no longer manufactured

They cannot provide the minimum 78% AFUE required by DOT

List the five furnace cabinet configurations

Up-flow, down-flow, horizontal, low boy, multi-position

list the five furnace cabinet configurations

Up-flow, down-flow, horizontal, low boy, multi-position

Can the furnace drain and the air-conditioning drain be run with a common drain?

Yes they can both be run into the same drain. If they are, the drain should besized for the air conditioning drain, which is larger.

Gas forced Warm air Furnace

upflow, lowboy, downflow or counterflow, horizontal, and multiposition.

List the different types of gas burners.

Atmospheric burners and power burners

List the four categories of gas-fired furnaces based on flue-gas temperature and pressure

Category I, Category II, Category III, and Category IV

define the four categories of gas-fired furnaces

Category I, Category II, Category III, and Category IV

Explain why furnace efficiencies jump from 80 percent to 90 percent.

Efficiencies above 80% cause condensation either in the furnace or in thevent. The flue gas for efficiencies below 90% is too hot for PVC vent. So thevent on a furnace between 80% and 90% must withstand high temperatureand water, making it impractical.

explain why furnace efficiencies jump from 80 percent to 90 percent

Efficiencies above 80% cause condensation either in the furnace or in thevent. The flue gas for efficiencies below 90% is too hot for PVC vent. So thevent on a furnace between 80% and 90% must withstand high temperatureand water, making it impractical.

Discuss the evolution of the heat exchanger

First heat exchangers were barrel shaped, then sectionalized were likeflattened barrels or clamshells, serpentine was further flattened withserpentine path added, tubular is made from tubing shaped in serpentineshape, stainless steel recuperative added to condense water

discuss the evolution of the heat exchanger

First heat exchangers were barrel shaped, then sectionalized were likeflattened barrels or clamshells, serpentine was further flattened withserpentine path added, tubular is made from tubing shaped in serpentineshape, stainless steel recuperative added to condense water

Discuss the operation of an atmospheric burner

Gas leaves the burner orifice as a jet that enters in the center of the burnerventure. Primary air is sucked in by the velocity of this gas stream. The gasand air mix in the venture and travel into the main burner body. Here, thegas-air mixture slows down and expands to fill the chamber. The mixtureleaves through the burner ports where it is ignited.

discuss the operation of an atmospheric burner

Gas leaves the burner orifice as a jet that enters in the center of the burnerventure. Primary air is sucked in by the velocity of this gas stream. The gasand air mix in the venture and travel into the main burner body. Here, thegas-air mixture slows down and expands to fill the chamber. The mixtureleaves through the burner ports where it is ignited.

What is the difference between an 80 percent efficient furnace and a 90 percent efficient furnace

Have an extra recuperative heat exchanger that condenses water out of the flue gas.

describe the operation of a 90 percent condensing furnace

Have an extra recuperative heat exchanger that condenses water out of the flue gas.

describe the operation of an 80 percent mid-efficiency furnace

Inducer starts, igniter glows, gas valve opens, indoor fan starts.

describe the operation of a standing-pilot, natural-draft furnace

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.