BPI Combustion Safety 4 — Questions and Answers
Question 1: What test is used to detect a cracked heat exchanger in a forced-air furnace?
- Blower door depressurization test
- CO measurement in supply air ducts while the furnace blower runs (Correct answer)
- Flue gas analysis at the draft hood
- Combustion air flow measurement
Correct answer: CO measurement in supply air ducts while the furnace blower runs
Measuring CO concentration in the supply air stream while the air handler runs can reveal combustion gases leaking through a cracked heat exchanger into conditioned air.
Question 2: Which standard establishes the minimum combustion air requirements for fuel-burning appliances in the US?
- ASHRAE 62.2
- NFPA 54 / National Fuel Gas Code (Correct answer)
- ICC International Mechanical Code section on ductwork
- EPA Method 19
Correct answer: NFPA 54 / National Fuel Gas Code
NFPA 54 (National Fuel Gas Code) sets requirements for combustion air sizing based on appliance BTU input and enclosure volume.
Question 3: Under the 'standard method' in NFPA 54, how much indoor air volume is required per 1,000 BTU/hr of combined appliance input if no outdoor air openings are provided?
- 10 cubic feet
- 50 cubic feet
- 100 cubic feet (Correct answer)
- 150 cubic feet
Correct answer: 100 cubic feet
NFPA 54 requires 50 cubic feet per 1,000 BTU/hr for the standard method, but the 'air from indoors' method (tightly constructed homes) requires 100 cubic feet per 1,000 BTU/hr.
Question 4: What is 'orphaned water heater' syndrome in the context of combustion safety?
- A water heater installed without a T&P relief valve
- A water heater left on a common vent after a furnace is replaced with a sidewall-vented unit (Correct answer)
- A tankless water heater operating without cold water supply
- A water heater with a failed thermocouple
Correct answer: A water heater left on a common vent after a furnace is replaced with a sidewall-vented unit
When a high-efficiency furnace is installed and no longer shares the masonry chimney, the remaining water heater may be undersized for the flue, causing poor draft and spillage.
Question 5: A CO alarm in the home is sounding at 70 ppm. According to BPI protocols, what is the first step?
- Identify the CO source with a combustion analyzer before doing anything else
- Evacuate all occupants and call emergency services (Correct answer)
- Open windows to dilute CO and then test appliances
- Turn off all appliances and wait 10 minutes before re-testing
Correct answer: Evacuate all occupants and call emergency services
Occupant safety is the priority; BPI requires immediate evacuation and emergency services notification when a CO alarm activates.
Question 6: What is the significance of the 'dew point' in flue gas analysis for high-efficiency condensing appliances?
- Flue gas must stay above dew point to prevent dangerous pressure buildup
- Condensing appliances intentionally cool flue gases below dew point to extract latent heat, requiring drain provisions (Correct answer)
- Flue gas dew point indicates incomplete combustion
- Dew point must be above 140°F to maintain chimney draft
Correct answer: Condensing appliances intentionally cool flue gases below dew point to extract latent heat, requiring drain provisions
Condensing furnaces and boilers cool flue gas below its dew point (~130°F for natural gas) to recover latent heat, producing acidic condensate that must be properly drained.
Question 7: Which of the following is a BPI-required pre-condition before performing weatherization work on a home with combustion appliances?
- Obtain a natural gas pressure reading from the utility
- Complete combustion safety testing and resolve any unsafe conditions first (Correct answer)
- Replace all atmospheric appliances with sealed-combustion units
- Install a whole-house mechanical ventilation system
Correct answer: Complete combustion safety testing and resolve any unsafe conditions first
BPI's 'test in / test out' protocol requires combustion safety to be assessed before weatherization begins so that tightening work does not worsen existing hazards.
BPI Combustion Safety 4
What test is used to detect a cracked heat exchanger in a forced-air furnace?