BAP BAP Combustion & Mechanical Systems 2 — Questions and Answers
Question 1: In a forced-air heating system, what does a high temperature rise across the heat exchanger typically indicate?
- Efficient combustion at design conditions
- Restricted airflow, often caused by a dirty filter or blocked ducts (Correct answer)
- Oversized ductwork reducing static pressure
- Excessive refrigerant charge in a dual-fuel system
Correct answer: Restricted airflow, often caused by a dirty filter or blocked ducts
A temperature rise above the manufacturer's specified range signals inadequate airflow, which stresses the heat exchanger and can lead to cracking and CO spillage.
Question 2: What does 'draft pressure' measure in a vented combustion appliance assessment?
- The gas supply pressure upstream of the appliance regulator
- The negative pressure in the flue that draws combustion gases upward and out (Correct answer)
- The static pressure difference between supply and return plenums
- The pressure differential across the heat exchanger during ignition
Correct answer: The negative pressure in the flue that draws combustion gases upward and out
Draft pressure is the negative pressure measured in the flue or vent connector that indicates how effectively combustion gases are being expelled from the appliance.
Question 3: Which appliance type is MOST resistant to backdrafting caused by house depressurization?
- Atmospherically vented water heater
- Power-vented water heater
- Sealed-combustion condensing furnace (Correct answer)
- Open-combustion gravity furnace
Correct answer: Sealed-combustion condensing furnace
Sealed-combustion appliances draw combustion air directly from outside through a dedicated pipe, making them immune to backdrafting from indoor pressure changes.
Question 4: A BAP analyst finds that a gas water heater's pilot flame is yellow and lazy. What does this most likely indicate?
- The thermocouple is failing and should be replaced
- Insufficient combustion air or a partially blocked burner orifice (Correct answer)
- The gas pressure is too high at the appliance regulator
- The flue is too short, causing excessive draft
Correct answer: Insufficient combustion air or a partially blocked burner orifice
A yellow, lazy pilot flame indicates incomplete combustion due to insufficient air supply or a partially clogged orifice, which can produce elevated CO.
Question 5: What is the function of a barometric damper on an oil-fired boiler's flue?
- To increase draft during cold outdoor temperatures
- To regulate draft and prevent excessive negative pressure in the flue (Correct answer)
- To seal the flue when the burner is off
- To measure flue gas temperature for efficiency calculations
Correct answer: To regulate draft and prevent excessive negative pressure in the flue
A barometric damper opens to admit room air into the flue, moderating excessive draft that could interfere with proper burner operation and efficiency.
Question 6: Which measurement tool is essential for verifying gas supply pressure at a combustion appliance during a BAP assessment?
- Infrared camera
- Manometer connected to the appliance test port (Correct answer)
- Clamp meter measuring burner amperage
- Combustion analyzer sampling exhaust gases
Correct answer: Manometer connected to the appliance test port
A manometer connected to the appliance's inlet pressure test port verifies that gas pressure falls within the manufacturer's specified operating range.
BAP BAP Combustion & Mechanical Systems 2
In a forced-air heating system, what does a high temperature rise across the heat exchanger typically indicate?