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 purpose of a refrigerant recovery machine? → To remove and store refrigerant from a system before service
2. 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
3. In load calculations, 'infiltration' refers to: → Uncontrolled air leakage into the building through gaps and cracks
4. What is the minimum AFUE required for a gas furnace to qualify as high-efficiency in the US? → 90%
5. What is 'balancing' a hydronic system? → Adjusting flow rates to each zone to ensure design heat delivery throughout the system
6. What role does collaboration play in electrical controls for HVAC professionals? → It enhances outcomes through diverse perspectives and shared expertise
7. What safety device shuts off a gas furnace if the heat exchanger area overheats? → High-limit switch
8. Under EPA Section 608 regulations, recovery cylinders must be hydrostatically tested every how many years? → 5 years
9. Which document typically outlines the compliance requirements for HVAC professionals? → Standards of practice and code of conduct
10. In a gas furnace, what is the purpose of the heat exchanger? → To separate combustion gases from the conditioned air while transferring heat
11. 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
12. What is the value of continuing education in thermodynamics for HVAC professionals? → It keeps professionals current with evolving standards and practices
13. What is the fundamental principle behind system design in the HVAC domain? → Balancing performance, reliability, and efficiency
14. What type of scale is required when charging an HVAC system by weight? → Refrigerant charging scale
15. Which professional attribute is most valued in ductwork within the HVAC field? → Accountability and commitment to standards
16. What does an enthalpy controller measure to determine if economizer free-cooling is beneficial? → Both outdoor air temperature and humidity to calculate total heat content
17. What is the value of continuing education in refrigeration for HVAC professionals? → It keeps professionals current with evolving standards and practices
18. What is the recommended first step when a HVAC professional identifies a compliance violation? → Document and report through proper channels
19. In a zone control system, what device modulates airflow to individual zones based on each zone's thermostat demand? → Zone damper or VAV box
20. In HVAC practice, what is the best approach to quality improvement in refrigeration? → Use data-driven methods with measurable outcomes
21. What is the Annual Fuel Utilization Efficiency (AFUE) rating used for? → Rating the seasonal efficiency of fossil-fuel heating equipment
22. In a multi-zone hydronic system using zone valves, when does the circulator pump operate? → When any zone valve opens and calls for heat
23. What is the most important professional competency for HVAC certification in refrigeration? → Deep knowledge combined with practical application skills
24. What communication protocol, standardized by ASHRAE, was specifically designed for building automation systems? → BACnet
25. Which of the following is an 'internal gain' source that adds to the cooling load in a building? → Occupants, lighting, and appliances
26. A clamp meter (clamp-on ammeter) measures current by detecting what around a conductor? → Magnetic field
27. What is the primary consideration when implementing changes to ventilation design? → Impact assessment and change management
28. Which documentation is essential when working with ventilation design in HVAC? → Detailed technical specifications and as-built diagrams
29. What does MERV stand for in air filter ratings? → Minimum Efficiency Reporting Value; higher = more efficient at capturing smaller particles
30. Which tool is used to measure the refrigerant pressure on both the high and low sides of an HVAC system simultaneously? → Manifold gauge set