HVAC Exam Study Guide 2026: 80+ Terms for EPA 608 & NATE

TL;DR

This HVAC exam study guide covers every critical term you need to know across the EPA 608, NATE, and state licensing exams. It’s organized by exam section rather than alphabetically, so you can focus your study time where it matters most. Each term includes exam context explaining how it typically shows up on the test. The EPA does not provide its own study guide, which makes resources like this essential for passing.

How to Use This Study Guide

Most HVAC exam study guides dump hundreds of terms into an alphabetical list and call it a day. That approach wastes your time. You end up scrolling past terms you’ll never see on your specific exam while missing the ones that actually trip people up.

This guide is different. Terms are grouped by exam section, and each definition includes a note about why the term matters on the test. Whether you’re preparing for the EPA 608, NATE Ready-to-Work, NATE CHP-5, or a state contractor exam, you can jump straight to the section that applies to you.

A few tips before you start:

• Bookmark this page. Use Ctrl+F (or Command+F on Mac) to search for specific terms during study sessions.

• Don’t just memorize, understand. As one HVAC instructor put it, “there is a big difference between practicing for an exam and studying for it. If you jump straight into taking practice quizzes without understanding the underlying laws and physics, you are just memorizing the letters A, B, C, and D.” Testing organizations rephrase questions, so understanding beats rote memorization every time.

• Pair this glossary with practice tests. Once you know the terms, test yourself under timed conditions.

Ready to start preparing? Check out SkillCat’s EPA 608 practice tests to see where you stand right now.

EPA 608 Exam Structure: What You’re Up Against

Before diving into terms, understand the test format. Section 608 of the Clean Air Act requires every technician who maintains, services, repairs, or disposes of equipment containing refrigerants to be certified. The EPA itself does not provide a study guide, which is why third-party resources are so important.

The EPA 608 exam has four sections, each with 25 multiple-choice questions. To earn Universal certification (the most common goal), you take all four sections for 100 questions total. You need at least 72% on each section to pass. If you take the Core section as an open-book exam, the passing threshold rises to 84%, and it cannot count toward Universal certification, since the Core must be proctored for that credential.

One fact that changes how you study: practitioners on Reddit consistently report that the EPA 608 draws from a pool of roughly 350 questions, with 25 randomly selected for each test section. This means you won’t see every possible question, but you need broad enough knowledge to handle whatever comes up.

Your Section 608 certification never expires once you earn it. That alone makes the time investment worth it.

EPA 608 Core Section Terms

The Core section appears on every version of the EPA 608 exam. These terms cover environmental science, regulations, refrigerant handling, and safety.

Environmental and Regulatory Terms

Ozone Depletion — The thinning of the Earth’s stratospheric ozone layer caused by chemicals like CFCs and HCFCs. Exam questions often ask which refrigerant types contribute to ozone depletion (CFCs and HCFCs do, HFCs do not).

Stratosphere — The atmospheric layer where the ozone layer exists, roughly 6 to 31 miles above Earth. Don’t confuse this with the troposphere, which is the layer closest to the ground.

Clean Air Act — The federal law that established Section 608 regulations. Expect questions about what the Clean Air Act requires of technicians, specifically the certification mandate.

Montreal Protocol — The international treaty that phased out production of ozone-depleting substances. The exam tests whether you know this is an international (not domestic) agreement.

SNAP Program (Significant New Alternatives Policy) — The EPA program that evaluates and approves substitute refrigerants. Questions typically ask what SNAP stands for or what its purpose is.

Section 608 — The specific section of the Clean Air Act that governs stationary refrigeration and air conditioning equipment. This is distinct from Section 609, which covers motor vehicle air conditioning (MVAC).

40 CFR Part 82 — The Code of Federal Regulations section that contains EPA refrigerant management rules. You probably won’t be asked to cite the number, but understanding that these rules carry the force of law matters.

📝 Exam tip: The EPA frequently tests dates. Venting of CFCs became illegal on July 1, 1992. Recovery equipment had to be certified by November 15, 1993. Memorize both.

Refrigerant Classification Terms

CFC (Chlorofluorocarbon) — Fully halogenated refrigerants like R-11 and R-12. They have the highest ozone depletion potential. Production has been banned in the United States since 1996.

HCFC (Hydrochlorofluorocarbon) — Partially halogenated refrigerants like R-22. Lower ODP than CFCs, but still harmful to the ozone layer. R-22 production was banned on January 1, 2010, and continues to be phased out. For a deeper look at modern replacements, read about R-410A and alternatives.

HFC (Hydrofluorocarbon) — Refrigerants like R-134a, R-410A, and R-404A. Zero ozone depletion potential, but high global warming potential. Subject to a phase-down, not a full ban.

HFO (Hydrofluoroolefin) — Newer refrigerants with very low GWP, designed as replacements for HFCs. R-1234yf is the most common example.

A2L Refrigerant — A classification for “mildly flammable” refrigerants. As HFCs phase down, A2L refrigerants like R-32 and R-454B are becoming more common. The exam increasingly includes questions about flammability classifications.

ODP (Ozone Depletion Potential) — A relative scale measuring how much a substance damages the ozone layer compared to R-11 (which has an ODP of 1.0). CFCs have the highest ODP, HFCs have zero.

GWP (Global Warming Potential) — A measure of how much heat a greenhouse gas traps in the atmosphere over a set time period. HFCs have zero ODP but high GWP, which is why they’re being phased down.

⚠️ Common confusion: Students often mix up ODP and GWP. Remember that CFC/HCFC damage ozone (ODP), while HFC traps heat (GWP). HFCs are “ozone-safe” but not “climate-safe.”

The Three Rs: Recovery, Recycling, and Reclaiming

This is the single highest-confusion area on the EPA 608. The exam tests whether you can distinguish between these three processes, and the differences are specific.

Recovery — Removing refrigerant from a system and storing it in an external container without necessarily cleaning or testing it. Any certified technician can recover refrigerant.

Recycling — Cleaning recovered refrigerant using basic processes like oil separation and moisture removal, then reusing it. The critical detail: recycled refrigerant can only be reused in equipment owned by the same person, or in equipment from which it was recovered.

Reclaiming — Processing recovered refrigerant to meet the ARI-700 purity standard. This must be done by an EPA-certified reclaimer. Reclaimed refrigerant can be resold as if it were new.

ARI-700 Standard — The purity specification that reclaimed refrigerant must meet. It establishes composition, contamination limits, and testing methods for fluorocarbon refrigerants. If an exam question asks about selling recovered refrigerant, the answer almost always involves ARI-700.

📝 Exam tip: A common trick question presents a scenario where someone wants to sell recovered refrigerant. The correct answer is always that it must first be reclaimed to ARI-700 standards by a certified reclaimer.

Safety Terms

De Minimis Release — A small, unavoidable release of refrigerant that occurs during normal equipment connection and disconnection. This is the only type of release that is legal under Section 608.

Venting Prohibition — The federal ban on knowingly releasing refrigerant into the atmosphere. Violations carry penalties up to $44,539 per day per violation. The exam asks when venting became illegal (July 1, 1992 for CFCs, November 15, 1995 for HCFCs and HFCs).

Phosgene Gas — A toxic gas produced when certain refrigerants come into contact with open flames or high-temperature surfaces. This is a safety question staple. If you see a question about the danger of using a torch near refrigerant lines, phosgene is the answer.

For a more complete walkthrough of the Core section, see this EPA Section 608 certification guide.

EPA 608 Type I Terms (Small Appliances)

Type I certification covers small appliances containing five pounds or less of refrigerant. Think window AC units, household refrigerators, dehumidifiers, and vending machines.

Small Appliance — Factory-charged equipment containing five pounds or less of refrigerant, manufactured, charged, and hermetically sealed in a factory. The “five pounds or less” threshold is the key exam fact.

Process Tube — A small-diameter tube used by the manufacturer to charge the system with refrigerant. Technicians use process tubes as access points for recovery.

Piercing Valve (Saddle Valve) — A valve clamped onto refrigerant tubing to provide an access point without cutting or brazing. Commonly used on small appliances that lack standard service valves.

Self-Contained Recovery Machine — A recovery device with its own internal compressor that actively pulls refrigerant from the appliance. Required when system-dependent recovery won’t achieve the necessary vacuum level.

System-Dependent Recovery — A recovery method that relies on the appliance’s own compressor or internal pressure to push refrigerant into the recovery container. Only works if the appliance compressor is operational.

⚠️ Common confusion: Type I questions often ask which recovery method to use based on whether the compressor works. If the compressor runs, system-dependent is an option. If not, you need a self-contained recovery machine.

EPA 608 Type II Terms (High-Pressure Systems)

Type II covers high-pressure appliances, the category that includes most residential and commercial HVAC systems. This is where the majority of working technicians spend their time.

High-Pressure Appliance — Equipment that uses a refrigerant with a boiling point between -50°C and 10°C at atmospheric pressure. R-22, R-410A, R-134a, and R-404A systems all fall into this category.

Leak Rate — The annual percentage of a system’s total charge that escapes as leaks. For systems containing 50 or more pounds of refrigerant, the EPA sets mandatory repair thresholds. This topic causes some of the highest failure rates on the exam, according to HVAC training providers.

Mandatory Repair Threshold — The annual leak rate that triggers a legal requirement to repair the leak. The specific percentages vary by equipment type (commercial vs. industrial vs. comfort cooling). Memorize these numbers.

Standing Pressure Test — A test where the system is pressurized with dry nitrogen and monitored for pressure drops over time. Used to locate leaks. The exam asks what gas to use (nitrogen, never oxygen or refrigerant) and why.

Superheat — The temperature of a refrigerant vapor above its saturation (boiling) point at a given pressure. Measuring superheat tells you if the evaporator is getting enough refrigerant. Too high means starved coil, too low means potential liquid floodback to the compressor.

Subcooling — The temperature of liquid refrigerant below its saturation (condensing) point at a given pressure. Subcooling tells you if the condenser is doing its job. Too little subcooling means the system may be undercharged. If you want to understand the electrical side of these systems, this guide on HVAC electrical components provides helpful diagrams.

Evacuation Level — The vacuum level a system must reach before recharging with refrigerant. The target is typically 500 microns. After reaching 500 microns, valve off the vacuum pump and watch whether the system holds. A rising reading indicates moisture or a leak.

Key Type II Refrigerants

R-22 — An HCFC refrigerant once dominant in residential AC. Production banned January 1, 2010 (with a full phase-out of production and import by 2020). Still exists in legacy systems. EPA 608 commonly tests R-22 phase-out dates.

R-410A — An HFC blend that replaced R-22 in new residential equipment. Operates at significantly higher pressures than R-22 (about 60% higher). Equipment designed for R-22 cannot use R-410A without modification.

R-134a — An HFC used widely in automotive AC (Section 609) and medium-temperature commercial refrigeration. Zero ODP but moderate GWP.

R-404A — An HFC blend used in commercial refrigeration (supermarket cases, walk-in coolers). High GWP, making it a target for phase-down.

EPA 608 Type III Terms (Low-Pressure Systems)

Type III covers low-pressure appliances, primarily large centrifugal chillers found in commercial and institutional buildings.

Low-Pressure Appliance — Equipment that uses a refrigerant with a boiling point above 10°C at atmospheric pressure. These systems often operate in a vacuum during normal operation.

Centrifugal Chiller — A large cooling system that uses a centrifugal compressor to chill water, which then circulates through the building for cooling. Most centrifugal chillers use low-pressure refrigerants like R-11 or R-123.

Purge Unit — A device on a low-pressure chiller that removes air and non-condensable gases from the system. Because low-pressure systems operate below atmospheric pressure, air leaks in (rather than refrigerant leaking out). A high-efficiency purge unit is critical for minimizing refrigerant loss.

Rupture Disc — A pressure relief device that bursts at a predetermined pressure to prevent catastrophic vessel failure. Unlike a relief valve, a rupture disc cannot reseal after activating, so it must be replaced.

Water-Cooled Recovery Unit — A recovery machine specifically designed for low-pressure refrigerants, which are often liquid at room temperature. Water cooling helps condense the refrigerant efficiently during recovery.

📝 Exam tip: Type III questions frequently focus on what makes low-pressure systems unique, specifically that they operate in a vacuum and that air leaks INTO the system rather than refrigerant leaking OUT. For more on low-pressure systems, see this Type III chiller guide.

HVAC System Fundamentals (Tested on All Exams)

These terms appear on the EPA 608, NATE exams, and state licensing tests. They represent the foundation of refrigeration and air conditioning science.

Refrigeration Cycle Components

Compressor — The “heart” of the refrigeration system. It compresses low-pressure refrigerant vapor into high-pressure, high-temperature vapor. The exam tests whether you know where the compressor sits in the cycle (between the evaporator outlet and condenser inlet).

Condenser — The component that rejects heat from the system. High-pressure refrigerant vapor enters, releases heat to the surrounding air (or water), and exits as high-pressure liquid.

Evaporator — The component that absorbs heat into the system. Low-pressure liquid refrigerant enters, absorbs heat from the space being cooled, and exits as low-pressure vapor.

Metering Device — The component that controls refrigerant flow into the evaporator. Creates the pressure drop that allows the refrigerant to expand and cool. Two common types:

• TXV (Thermostatic Expansion Valve) — Adjusts refrigerant flow based on superheat at the evaporator outlet. Used in most residential and commercial systems.

• Capillary Tube — A fixed-length, small-diameter tube that creates a constant restriction. Common in window units and refrigerators. No moving parts.

Measurement Terms

BTU (British Thermal Unit) — The amount of heat needed to raise one pound of water by one degree Fahrenheit. The basic unit of heating and cooling capacity.

Ton of Cooling — Equal to 12,000 BTU per hour. A standard 3-ton residential AC system provides 36,000 BTU/hr of cooling. This conversion shows up on nearly every HVAC exam.

PSI (Pounds per Square Inch) — The standard unit for measuring pressure. On exams, you need to distinguish between PSIG (gauge pressure, relative to atmospheric) and PSIA (absolute pressure, including atmospheric pressure).

Micron — A unit of vacuum measurement. One micron equals 1/1000 of a millimeter of mercury. Systems should be evacuated to 500 microns before charging. A micron gauge is the proper instrument for verifying evacuation depth.

Inches of Mercury (in. Hg) — Another vacuum measurement unit, coarser than microns. Used for initial evacuation. The exam asks which tool to use for final evacuation verification (micron gauge, not a compound gauge reading in. Hg).

Thermodynamic Terms

Latent Heat — Heat energy that changes a substance’s state (liquid to gas, or gas to liquid) without changing its temperature. This is how refrigeration works: the evaporator absorbs latent heat to boil refrigerant.

Sensible Heat — Heat energy that changes a substance’s temperature without changing its state. When you feel warm air, that’s sensible heat.

Saturation Temperature/Pressure — The temperature and pressure at which a refrigerant changes between liquid and vapor states. At saturation, both liquid and vapor exist simultaneously. Every pressure corresponds to a specific saturation temperature for a given refrigerant.

Electrical Terms

Ohm’s Law — The relationship between voltage (V), current (I), and resistance ®: V = I × R. Tested on NATE exams and most state licensing exams. You need to be able to calculate any one value given the other two.

Capacitor — An electrical component that stores energy and provides the extra starting torque for compressor and fan motors. Two types tested: start capacitors (used only during startup, then disconnected) and run capacitors (used continuously during operation).

Contactor — An electrically controlled switch that connects power to the compressor and outdoor fan motor. When the thermostat calls for cooling, it energizes the contactor coil, which pulls in the contacts and completes the circuit.

Relay — Similar to a contactor but used for lower-voltage or lower-amperage circuits. The exam distinguishes between relays (lighter duty) and contactors (heavier duty).

Transformer — A device that steps voltage up or down. In HVAC, transformers typically step 240V line voltage down to 24V for the control circuit. The exam asks about the relationship between primary and secondary windings.

If you’re looking for a broader study plan that covers all these fundamentals, this EPA 608 study schedule breaks the material into manageable daily sessions.

NATE Certification Terms

NATE (North American Technician Excellence) certification is voluntary, but it signals competence to employers and often translates to higher pay.

KATE (Knowledge Areas of Technician Expertise) — The detailed outlines that define what NATE tests. Every NATE exam question traces back to a KATE document. If a topic isn’t in the KATE, it won’t be on the test. This is your study roadmap.

CHP-5 Pathway — NATE’s certification path that requires five separate exams: HVAC Fundamentals, Electrical and Controls, Comfort and Airflow, Installation, and Service. This replaced the older two-exam format.

Ready-to-Work (RTW) Certificate — NATE’s entry-level credential designed for technicians just entering the field with little or no formal training. It costs $60, includes 50 questions, and is taken online without proctoring. NATE provides a downloadable study guide when you order the exam.

HVAC Support Technician — A NATE credential for technicians who assist senior techs but aren’t yet performing independent service work.

ICE Certification — NATE exams are accredited by the Institute for Credentialing Excellence, which verifies that the testing process meets national psychometric standards.

CEU (Continuing Education Unit) — NATE certifications require ongoing education for renewal. NATE Core certification is valid for 5 years, while specialty certifications last 2 years. CEUs keep your credential current.

📝 Exam tip: Unlike EPA 608 certification, NATE certifications do expire. Plan for renewal well in advance.

For a complete walkthrough of NATE pathways and requirements, read this NATE certification guide.

State Licensing and Career Terms

Understanding the difference between certification and licensing is one of the most confused topics in HVAC. This HVAC exam study guide wouldn’t be complete without clearing it up.

Certification vs. License — Certifications (like EPA 608 and NATE) demonstrate competency in specific knowledge areas. Licenses are legal permissions granted by a state or municipality to perform certain work. You can hold certifications without a license, and some states require both. The key difference: certifications are national, licenses are local.

Journeyman License — A state-issued license that allows a technician to perform HVAC work independently (without direct supervision). Requirements vary wildly. Some states require thousands of hours of supervised experience plus an exam. Seventeen states don’t require an HVAC license at all, and eight more don’t offer statewide licenses.

Master License — A higher-tier license that typically allows a technician to supervise journeymen, pull permits, and operate as a contractor. Usually requires additional years of experience beyond the journeyman level.

Contractor License — A business-level license that authorizes an HVAC company to bid on and perform work. Often requires the business owner (or a designated qualifying agent) to hold a master or contractor-level certification.

Apprentice — A technician working under the supervision of a licensed journeyman or master while gaining the experience hours required for their own license. Many states have formal apprenticeship programs with defined hour requirements (typically 4,000 to 8,000 hours).

OSHA-10 — A 10-hour safety training course developed by the Occupational Safety and Health Administration. While not an HVAC-specific certification, many employers require it. Some states and municipalities mandate OSHA-10 for anyone working on construction sites.

For a broader look at HVAC career paths after you pass your exams, this HVAC technician career guide covers salary expectations, job types, and advancement opportunities.

Study Strategy Terms

These aren’t HVAC terms, but understanding them helps you study smarter.

Proctored Exam — An exam supervised by an approved proctor, either in person or via remote monitoring. EPA 608 Universal certification requires a proctored Core exam. You cannot use an open-book Core score for Universal.

Open-Book Exam — A test where reference materials are allowed. Some EPA-approved testing organizations offer open-book options for individual sections (not Core for Universal). The passing threshold is higher at 84%.

Remote Proctoring — Taking a proctored exam online while being monitored via webcam and screen recording. This format has become common for EPA 608 testing. Learn more about how remote proctoring works.

Diagnostic Quiz — A pre-study assessment that identifies your weak areas before you start focused preparation. Taking a diagnostic quiz first prevents wasting time on topics you already know.

Practice Test — A simulated exam using questions formatted like the real test. The most effective study strategy is cycling between learning terms, taking practice tests, reviewing mistakes, and retesting.

Quick-Reference Table: HVAC Exam Comparison

Putting It All Together

This HVAC exam study guide covered over 80 terms across the EPA 608, NATE, and state licensing exams. But knowing definitions is only the first step. The practitioners who pass on their first attempt combine three things: they understand the concepts behind each term, they take enough practice tests to recognize how questions are phrased, and they focus extra time on high-failure topics like leak rate thresholds, refrigerant classifications, and the three Rs.

Practitioners on Reddit consistently emphasize that the EPA 608 is very passable if you put in focused study time. One technician wrote that passing “is not hard, especially if you can memorize things easily.” But the smarter approach is understanding rather than pure memorization, because different testing organizations rephrase the same concepts in different ways.

If you’re ready to move from studying terms to actually earning your certification, SkillCat offers EPA 608 training and certification entirely on your phone, including interactive lessons, practice tests, and the proctored exam.

Frequently Asked Questions

Does the EPA provide an official study guide for the 608 exam?

No. The EPA does not provide a study guide. This is confirmed on the EPA’s own Q&A page. The agency sets the rules and approves testing organizations, but study materials come from third-party providers, training platforms, and community resources.

What score do you need to pass the EPA 608 exam?

You need at least 72% on each section when taking the exam as a closed-book, proctored test. If you take an open-book version, the passing score is 84%. Each section has 25 questions, so 72% means you need at least 18 correct answers per section.

Does EPA 608 certification expire?

No. Once you earn your EPA Section 608 certification, it is valid for life. There are no renewal requirements or continuing education obligations. This is different from NATE certifications, which expire after 2 to 5 years depending on the credential type.

What is the difference between recovery, recycling, and reclaiming?

Recovery means removing refrigerant from a system into an external container. Recycling means cleaning recovered refrigerant using basic filtration and reusing it in the same owner’s equipment. Reclaiming means processing refrigerant to meet ARI-700 purity standards, which must be done by an EPA-certified reclaimer. Only reclaimed refrigerant can be resold.

How many questions are in the EPA 608 question pool?

Practitioners on Reddit and HVAC forums consistently report that the exam draws from a pool of approximately 350 questions. Each section randomly selects 25 from this pool, meaning you’ll get a different mix each time you take the test.

What is the difference between HVAC certification and a license?

Certifications (like EPA 608 and NATE) are credentials that prove your knowledge in specific areas and are recognized nationally. Licenses are legal permissions granted by state or local governments that authorize you to perform HVAC work in a specific jurisdiction. Seventeen states don’t require an HVAC license, but EPA 608 is required everywhere in the United States.

Which HVAC exam should I take first?

Start with the EPA 608. It’s the only federally required certification, and you can’t legally work with refrigerants without it. After that, consider NATE’s Ready-to-Work certificate if you’re new to the field, or pursue your state’s licensing exam if your state requires one. For a step-by-step roadmap, check out this guide on how to get HVAC certified.

Can I study for the EPA 608 on my phone?

Yes. Mobile-friendly study guides, flashcard apps, and training platforms have made phone-based studying the norm. Many technicians on Reddit report studying and even completing their EPA 608 certification entirely from their phones during breaks or downtime.