HVAC Heating Systems

Question 1

What is the Annual Fuel Utilization Efficiency (AFUE) rating used for?

Accepted Answer

Rating the seasonal efficiency of fossil-fuel heating equipment

Answer

AFUE measures how efficiently a furnace or boiler converts fuel into heat over a heating season, expressed as a percentage.

Question 2

What is the minimum AFUE required for a gas furnace to qualify as high-efficiency in the US?

Accepted Answer

90%

Answer

Gas furnaces with an AFUE of 90% or higher are considered high-efficiency (condensing) furnaces, while standard efficiency is around 80% AFUE.

Question 3

In a gas furnace, what is the purpose of the heat exchanger?

Accepted Answer

To separate combustion gases from the conditioned air while transferring heat

Answer

The heat exchanger transfers heat from combustion gases to the circulating air supply while keeping the two airstreams completely separated.

Question 4

What type of venting is typically required for a 90%+ AFUE condensing gas furnace?

Accepted Answer

PVC plastic pipe venting

Answer

Condensing furnaces produce cool, acidic flue gases that require PVC plastic pipe for safe venting rather than traditional metal flue pipes.

Question 5

What is the ignition system called that replaced the standing pilot light in modern gas furnaces?

Accepted Answer

Hot surface ignitor (HSI)

Answer

Hot surface ignitors (HSI) replaced standing pilots in modern furnaces, using an electrically heated silicon nitride or silicon carbide element to ignite the burner.

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HVAC Heating Systems