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FC Cheat Sheet 2026

The 30 highest-yield FC facts, distilled from real exam questions. Print it, save it as a PDF, or study it here β€” free, no sign-up.

  1. What can cause a heating system to blow cold air instead of warm air? β†’ The furnace is malfunctioning or lacks sufficient fuel
  2. Why is it important to check the air filters during heating system maintenance? β†’ To ensure efficient airflow and prevent overheating
  3. What is the first step in troubleshooting a heating system? β†’ Inspect the furnace and check for obvious issues
  4. What does the 99% outdoor design temperature represent in a heating load calculation? β†’ The temperature that is equaled or exceeded only 1% of the hours in the heating season
  5. What is the purpose of the pressure switch on an induced-draft furnace? β†’ To confirm the inducer motor is creating proper draft before allowing ignition
  6. What is the minimum upward slope required for horizontal sections of Category I single-wall vent connector pipe? β†’ 1/4 inch per foot rise toward the chimney or vertical vent
  7. What is the purpose of the concentric vent system on a direct-vent condensing furnace? β†’ To use one pipe for exhaust and a surrounding outer pipe for combustion air intake
  8. What is the required clearance around a furnace as per safety standards? β†’ There should be a specified clearance based on the manufacturer’s guidelines
  9. Which test method uses a chemical tracer gas introduced into the combustion side to detect heat exchanger cracks? β†’ Tracer gas leak test (e.g., nitrogen with halide detector)
  10. Which type of ignition system uses a resistance element heated to approximately 1,800Β°F to ignite the gas? β†’ Hot surface igniter
  11. What is the maximum recommended oversizing percentage for a gas furnace according to ACCA Manual S guidelines? β†’ 40%
  12. Why is it important to use an energy-efficient furnace? β†’ To lower energy costs and environmental impact
  13. When adding a new supply run to an existing duct system, what must be verified to prevent degrading other rooms? β†’ That the existing system has sufficient blower capacity to handle the added airflow load
  14. What does 'design temperature difference' (Ξ”T) mean in the context of heating load calculations? β†’ The difference between indoor design temperature and outdoor design temperature
  15. How do you maintain the furnace blower motor? β†’ Lubricate, inspect, and ensure proper alignment
  16. What causes delayed ignition (a loud boom or puff) when a furnace starts up? β†’ Gas accumulating in the combustion chamber before igniting
  17. What is the purpose of a burner orifice in a gas furnace? β†’ To meter the correct amount of gas into the burner
  18. What is the primary cause of high static pressure in a residential duct system? β†’ Restrictive air filter, undersized ducts, or excessive elbows
  19. What is the primary danger of a blocked or restricted furnace flue vent? β†’ Combustion gases including carbon monoxide will spill into the living space
  20. What should be done if a furnace is not igniting? β†’ Inspect the ignition system and gas valve
  21. In Manual J calculations, which ACCA manual is used after the load is determined to properly select furnace equipment? β†’ Manual S
  22. Why is air balancing important after furnace installation? β†’ To ensure optimal airflow and system efficiency
  23. What is the maximum total external static pressure (TESP) typically allowed for a residential furnace? β†’ 0.5 inches W.C.
  24. When sealing duct joints and seams, which material is approved by most building codes and SMACNA standards? β†’ UL 181-rated mastic or foil tape
  25. What minimum flame signal (microamps DC) is typically required for a furnace flame sensor to keep the gas valve open? β†’ 0.5–1.0 Β΅A
  26. Why is checking the blower motor essential during maintenance? β†’ To improve system performance
  27. When performing a load calculation for a home addition, what must the technician verify about the existing furnace? β†’ Whether the existing furnace has sufficient capacity to handle the additional load
  28. What does a rollout switch do when it trips? β†’ Shuts off the gas valve because flames have rolled out of the combustion chamber
  29. Gas supply piping to a furnace must be tested for leaks using which method? β†’ Soapy water solution or listed leak detection fluid
  30. How does a home's infiltration rate affect the heating load calculation? β†’ Higher infiltration increases heating load by introducing cold outside air
Turn these facts into recall:
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