BPI Heating, Ventilation & Air Conditioning (HVAC) 2 — Questions and Answers
Question 1: What is the primary purpose of a heat exchanger in a forced-air furnace?
- To filter combustion byproducts from supply air
- To transfer heat from combustion gases to supply air without mixing them (Correct answer)
- To recirculate flue gases back into the burner
- To regulate refrigerant pressure in the system
Correct answer: To transfer heat from combustion gases to supply air without mixing them
The heat exchanger separates combustion gases from the air supply while transferring heat, preventing CO and other combustion byproducts from entering living spaces.
Question 2: A homeowner reports that their condensing furnace drains are backing up. What is the MOST likely cause?
- High static pressure in the duct system
- Blocked or kinked condensate drain line (Correct answer)
- Undersized flue vent pipe
- Failed inducer motor
Correct answer: Blocked or kinked condensate drain line
Condensing furnaces produce acidic condensate that must drain freely; a blocked or kinked drain line is the most common cause of backup.
Question 3: Which BPI diagnostic tool is used to measure airflow at supply and return registers?
- Manometer
- Combustion analyzer
- Flow hood (capture hood) (Correct answer)
- Infrared camera
Correct answer: Flow hood (capture hood)
A flow hood (capture hood) is placed over registers to measure the volume of air flowing through them in CFM.
Question 4: What does a high CO2 reading in flue gas analysis typically indicate?
- Incomplete combustion due to excess air
- Efficient combustion with proper air-fuel ratio (Correct answer)
- A cracked heat exchanger
- Insufficient draft pressure
Correct answer: Efficient combustion with proper air-fuel ratio
Higher CO2 in flue gases (up to the stoichiometric maximum) generally indicates more complete combustion and a better air-fuel mixture.
Question 5: What is the standard minimum ventilation rate prescribed by ASHRAE 62.2 for a 1,500 sq ft home with 3 occupants?
- 25 CFM
- 45 CFM (Correct answer)
- 60 CFM
- 75 CFM
Correct answer: 45 CFM
ASHRAE 62.2 calculates minimum ventilation as 0.03 CFM/sq ft × floor area + 7.5 CFM × (bedrooms + 1); for a 1,500 sq ft, 3-bedroom home this equals approximately 45 CFM.
Question 6: When performing a combustion safety test, what condition defines a worst-case depressurization scenario?
- All windows open and HVAC off
- All exhaust fans on, fireplace damper open, and largest return air pathway closed (Correct answer)
- Furnace running at full capacity with doors closed
- Supply registers fully open and return registers blocked
Correct answer: All exhaust fans on, fireplace damper open, and largest return air pathway closed
Worst-case depressurization combines all exhaust devices operating simultaneously with interior pathways that maximize negative pressure near combustion appliances.
Question 7: A heat pump's Heating Season Performance Factor (HSPF) measures:
- The ratio of heat output to electricity input over a cooling season
- The ratio of total heating output to total electricity consumed over a heating season (Correct answer)
- The efficiency of the compressor under peak load conditions
- The coefficient of performance at 47°F outdoor temperature
Correct answer: The ratio of total heating output to total electricity consumed over a heating season
HSPF is a seasonal metric that represents total Btu of heat delivered divided by total watt-hours of electricity consumed over an entire heating season.
BPI Heating, Ventilation & Air Conditioning (HVAC) 2
What is the primary purpose of a heat exchanger in a forced-air furnace?