HVAC Cheat Sheet 2026

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

1. What is the primary reason that refrigerant vapor is compressed in the refrigeration cycle? → To raise its pressure and temperature so it can reject heat at a higher temperature
2. A return air grille is significantly undersized. What is the most likely symptom in the living space? → Negative pressure in the room causing doors to slam shut or stick
3. What is the primary purpose of a refrigerant recovery machine? → To remove and store refrigerant from a system before service
4. Which type of hydronic terminal unit uses a fan to distribute heat from the hot water coil to the room? → Fan coil unit
5. Which venting category applies to a non-condensing gas furnace with a flue gas temperature above 300°F and negative vent pressure? → Category I
6. What is the purpose of a thermostatic expansion valve (TXV) in a refrigeration system? → Meter refrigerant flow to maintain superheat at the evaporator outlet
7. What must a technician do if they discover a leak in a commercial or industrial refrigeration system with a charge of more than 50 lbs? → Repair the leak within 30 days or implement a retrofit or retirement plan
8. When sizing a hydronic circulator pump, which two parameters are most critical? → Flow rate (GPM) and head pressure (feet of head)
9. Which ventilation strategy introduces 100% outdoor air and exhausts 100% of return air, with no recirculation? → Once-through system
10. In load calculations, 'infiltration' refers to: → Uncontrolled air leakage into the building through gaps and cracks
11. When installing a rooftop HVAC unit in a seismic design category D zone, which additional requirement applies per the International Mechanical Code? → Seismic bracing and anchorage
12. R-744 is the refrigerant designation for which substance? → Carbon dioxide
13. A technician notices supply air temperature drops 8°F between the air handler and a distant register. What is the most likely cause? → Inadequate duct insulation allowing heat gain or loss
14. Which type of recovery equipment must be used when the refrigerant system's compressor is operational? → System-dependent (passive) recovery equipment
15. Sick Building Syndrome (SBS) is most directly associated with which HVAC-related cause? → Inadequate ventilation and accumulation of indoor pollutants
16. What is the minimum AFUE required for a gas furnace to qualify as high-efficiency in the US? → 90%
17. What is 'balancing' a hydronic system? → Adjusting flow rates to each zone to ensure design heat delivery throughout the system
18. What role does collaboration play in electrical controls for HVAC professionals? → It enhances outcomes through diverse perspectives and shared expertise
19. A technician reads 22 psi static pressure at the boiler on a cold system. After firing the boiler, pressure rises to 28 psi. This indicates: → Normal system operation with thermal expansion
20. What safety device shuts off a gas furnace if the heat exchanger area overheats? → High-limit switch
21. What does the term 'ton of refrigeration' represent? → 12,000 BTU/hr of heat removal capacity
22. Under EPA Section 608 regulations, recovery cylinders must be hydrostatically tested every how many years? → 5 years
23. Which document typically outlines the compliance requirements for HVAC professionals? → Standards of practice and code of conduct
24. In a gas furnace, what is the purpose of the heat exchanger? → To separate combustion gases from the conditioned air while transferring heat
25. What safety information must HVAC technicians review before handling any new chemical, including refrigerants and cleaners? → The Safety Data Sheet (SDS) for that specific chemical
26. In HVAC design, 'face velocity' refers to: → Airflow velocity across the face area of a coil or filter
27. Which type of compressor uses rotating scrolls to compress refrigerant and is commonly found in modern residential heat pumps? → Scroll compressor
28. What is the purpose of a demand-controlled ventilation (DCV) system? → To modulate outdoor air intake based on real-time CO2 or occupancy sensors
29. What type of valve is used at each terminal unit in a hydronic system to allow the system to be balanced by limiting flow through high-flow circuits? → Globe valve or circuit setter
30. What is the primary function of an expansion tank in a closed-loop hydronic heating system? → To accommodate the volume increase of water as it heats and expands