- What the Professional Written Exam Actually Covers
- How to Read the Eight Domain Lines
- Domain 1: Combustion Theory and Heating Fuels
- Domains 2, 7 and 8: The Carbon Monoxide Cluster
- Domains 3 and 4: Building Pressure
- Domains 5 and 6: Combustion Gas and General Knowledge
- Format, Prerequisites and Fee Labels
- Sequencing the Domains Across Your Prep
- What We Could and Could Not Verify
- Frequently Asked Questions
- The certification is the ESCO Group Professional Level written exam, administered through HVAC Excellence: 100 closed-book questions.
- The catalog lists eight topic phrases; they are unweighted, so do not assume equal or fixed percentages.
- Carbon monoxide appears three separate times in the topic list: safety, general knowledge, and a final standalone entry.
- Building pressure is split into measurements and general knowledge, so expect both hands-on readings and conceptual questions.
What the Professional Written Exam Actually Covers
Before dissecting the content areas, it helps to pin down exactly which credential we are discussing. This guide covers the Combustion Analysis Certification issued by ESCO Group and administered through HVAC Excellence, specifically the Professional Level - Written Combustion Analysis examination. It is the credential listed in the federal career databases under the identifier 6153-A, and it is distinct from the Employment Ready Carbon Monoxide & Combustion Analysis exam and from any Master Specialist hands-on assessment. If you are still orienting yourself, our primer What Is Combustion Analysis Certification? gives the big-picture view, and our main certification overview ties the pieces together.
The examination description in the ESCO Institute - HVAC Excellence 2026 catalog (page 12) lists eight topic phrases. This article reproduces all eight as "domains" for study purposes. One important honesty note up front: these are the issuer's published summary topics. They are not a retrieved detailed blueprint, they carry no published percentage weights, and they should not be mistaken for an official eight-domain allocation of exam questions.
How to Read the Eight Domain Lines
The eight phrases in the catalog read, in order: combustion theory and heating fuels; carbon monoxide safety; building pressure measurements; building pressure general knowledge; combustion gas; combustion general knowledge; carbon monoxide general knowledge; and carbon monoxide. The final entry is listed on its own, and this guide keeps it as written rather than guessing at an extension the source does not provide.
The issuer's current Professional web page compresses the same description into five groups, folding "building pressure measurements" together with "general knowledge" and doing similar with the combustion gas entries. The catalog's more detailed wording is the better study map because it preserves distinctions that the compressed version hides. Here is how the eight lines cluster:
| Domain | Cluster | Likely Question Flavor |
|---|---|---|
| 1. Combustion theory and heating fuels | Foundations | Conceptual: what burns, how, and why |
| 2. Carbon monoxide safety | Carbon monoxide | Applied: hazard recognition and protective action |
| 3. Building pressure measurements | Building pressure | Procedural: taking and interpreting readings |
| 4. Building pressure general knowledge | Building pressure | Conceptual: why pressure behaves as it does |
| 5. Combustion gas | Combustion gas | Analytical: what flue gas readings indicate |
| 6. Combustion general knowledge | Combustion gas | Conceptual: broader combustion principles |
| 7. Carbon monoxide general knowledge | Carbon monoxide | Conceptual: properties, sources, effects |
| 8. Carbon monoxide | Carbon monoxide | Retained as the catalog's final listed entry |
The "likely question flavor" column is a study heuristic derived from the topic names, not an issuer statement about item types. The issuer does confirm that its exams use a multiple-choice format, so expect single-best-answer questions rather than essays or practical demonstrations.
Domain 1: Combustion Theory and Heating Fuels
Combustion Theory and Heating Fuels
This is the conceptual bedrock. Every flue gas reading and every pressure problem later in the exam makes more sense when you understand what combustion needs and what it produces.
- The fuels commonly burned in heating appliances and how their composition affects combustion products
- The relationship among fuel, air, and ignition, and what happens when the balance shifts
- Time, temperature, and turbulence as the factors that govern complete combustion
- Complete versus incomplete combustion and the byproducts of each
The supporting reference ESCO publishes, Combustion Analysis & Fuel Efficiency by Erik Rasmussen (ISBN 978-1-930044-25-8), opens with chapters titled "The Fuels of Combustion," "Combustion," and "Time - Temperature - Turbulence." Those chapter titles are a useful guide to how the subject is taught, though they are supporting curriculum rather than official exam domains. Only the publicly available sample of that manual was reviewed for this guide, so consult the full text yourself rather than assuming this summary captures everything in it.
If you are new to the vocabulary, our explainer on what a combustion analysis is walks through the basics in plain language before you tackle the exam-level material.
Domains 2, 7 and 8: The Carbon Monoxide Cluster
Carbon monoxide is the most heavily repeated subject in the topic list. It appears as "carbon monoxide safety," as "carbon monoxide general knowledge," and as a final standalone "carbon monoxide" entry. Whatever the reason for the repetition, the practical takeaway is clear: a candidate who treats CO as a single chapter to skim is taking an unnecessary risk.
Carbon Monoxide Safety (Domain 2)
This line points to the protective side of the work: recognizing hazardous conditions and responding correctly.
- How CO is produced in fuel-burning appliances and the conditions that raise production
- Safe testing practices when measuring in occupied spaces
- Appropriate response when readings indicate a hazard
- Communicating risk to occupants and documenting findings
Carbon Monoxide General Knowledge (Domain 7)
Expect background and principles rather than step-by-step procedures.
- Properties of carbon monoxide and why it is difficult to detect without instruments
- Common sources inside and outside the appliance
- The difference between ambient-air readings and flue-gas readings, and why each matters
- Why instrument selection and calibration affect the trustworthiness of results
Carbon Monoxide (Domain 8)
The catalog lists this as its closing entry without further elaboration. The safest preparation is to review CO across every angle: sources, measurement, interpretation, and safety response. Do not assume this line duplicates Domains 2 and 7 exactly.
The supporting manual's final chapter is titled "Carbon Monoxide Safety," which reinforces how central the topic is to the discipline. For a broader look at the field this knowledge feeds into, see our overview of combustion analysis jobs.
Domains 3 and 4: Building Pressure
Building pressure is split into two entries in the catalog: measurements and general knowledge. That split is meaningful. One is about the act of measuring; the other is about understanding why buildings behave the way they do.
Building Pressure Measurements (Domain 3)
Think of this as the procedural half: how readings are taken and what they mean once you have them.
- How pressure differences between spaces and the outdoors are measured
- Reading and interpreting manometer-style results correctly, including sign and magnitude
- Recognizing when a measurement setup is flawed or misleading
- Relating a pressure reading to the likelihood of spillage or backdrafting
Building Pressure General Knowledge (Domain 4)
This is the explanatory half, covering the causes behind the readings.
- How exhaust fans, duct leakage, and stack effect influence pressure inside a structure
- Why a tight building changes how combustion appliances draw air and vent
- The interaction between building pressure and draft
- Why pressure problems can create carbon monoxide hazards even when an appliance is properly adjusted
One source caveat is worth flagging here. ESCO's undated Combustion Analysis & Fuel Efficiency training page describes 50-question Employment Ready and Professional examinations built around building-pressure and CAZ (combustion appliance zone) topics. The exam-specific Professional table and the September 2026 catalog support a 100-question count, which is the figure this guide uses. If you see 50 questions quoted elsewhere, that is the conflicting description, not a different version of this exam. Our difficulty guide discusses how the length of the exam affects pacing.
Domains 5 and 6: Combustion Gas and General Knowledge
Combustion Gas (Domain 5)
This is where analyzer data becomes diagnostic information.
- Reading and interpreting flue gas constituents such as oxygen, carbon dioxide, and carbon monoxide
- How stack temperature relates to efficiency and what unusual readings suggest
- Using readings to judge whether an appliance is burning cleanly and efficiently
- Where and how to sample so that results represent the actual flue gas
Combustion General Knowledge (Domain 6)
This line is the broad conceptual companion to the gas readings.
- Draft and its role in moving combustion products out of the building
- Adjustment and verification: what to change, and how to confirm the result
- How air supply, venting, and appliance condition combine to affect safe operation
- Efficiency concepts and what they imply for fuel use
The supporting manual's chapter titles include "Combustion Testing," "Testing, Adjustment and Verification," "Draft," and "Stack Temperature & Efficiency." These align well with the practical content of Domains 5 and 6, but again they are study aids, not official exam categories.
Key Takeaway
Do not memorize flue gas numbers in isolation. Build the habit of asking what each reading says about air supply, fuel quality, venting, and safety. Questions in this area typically reward interpretation over recall.
Format, Prerequisites and Fee Labels
Knowing the content is only half the battle; you also need to qualify and register correctly. According to the issuer's Professional page and catalog, the examination is a 100-question, closed-book written test in multiple-choice format. Candidates must have at least two years of verified field experience and must hold the separate Principles of Electrical and Refrigeration Theory CORE examination as a prerequisite. Passing candidates receive a Certificate of Achievement. For a deeper walk-through of eligibility, see our requirements guide.
Delivery is described in the catalog's testing-options section as proctored online or paper-based. You arrange your chosen route through an approved proctor. The catalog's page 12 lists three distinct price labels for Professional examinations:
| Catalog Label | Amount (USD) |
|---|---|
| Retail | $130 |
| Online Exam | $40 |
| Paper Exam | $50 |
Several items were not verified from the issuer sources reviewed: a Professional Combustion Analysis timer, a passing threshold, and a renewal rule. This guide therefore makes no claims about them. If you want to see what is and is not published, our article on the passing score addresses the gap candidly, and the exam dates guide covers scheduling considerations.
Sequencing the Domains Across Your Prep
Since the exam is unweighted as published, a sensible plan builds knowledge in dependency order rather than guessing at emphasis. Here is one way to stage the eight domains over four weeks, tied to how the topics build on each other.
Foundations: Domains 1 and 6
- Fuels, the fuel-air-ignition relationship, and time-temperature-turbulence
- Draft, adjustment, and verification concepts
Gas Analysis: Domain 5
- Flue gas constituents and what each indicates
- Stack temperature and efficiency interpretation
Building Pressure: Domains 3 and 4
- Measurement procedure and reading interpretation
- Causes of pressure imbalance and their effect on venting
Carbon Monoxide: Domains 2, 7 and 8
- Safety response, sources, and measurement
- Full-length practice under closed-book conditions
The reasoning: carbon monoxide questions often depend on understanding combustion, gas readings, and pressure, so placing that cluster last lets it draw on everything before it. Because CO appears three times in the topic list, give it the longest review block and revisit it briefly in the final days. For a fuller preparation framework, see our study guide, and keep our cheat sheet handy for last-minute review. When you are ready to test yourself against exam-style questions, try the Combustion Analysis practice tests.
What We Could and Could Not Verify
Responsible exam prep means knowing the limits of your sources. Here is where this guide's information comes from and where it stops:
- Topic list: Taken from the ESCO Institute - HVAC Excellence 2026 catalog, page 12. It is a summary of examination topics, not an itemized blueprint.
- Detailed objectives: The issuer links a Competency and Task List workbook, but its contents could not be retrieved, so no unseen objectives or percentages have been reconstructed here.
- Question count: 100 questions, supported by the exam-specific table and the catalog, in contrast to an undated training page that describes 50.
- Not verified: Timer, passing threshold, and renewal rules.
- Supporting manual: Only the public sample of the Rasmussen text was inspected, not the complete paid manual.
Sources were checked on October 5, 2026. Because issuers update catalogs, confirm details on the official Professional Technician Certifications page before you register. Curious how the credential translates to the job market? Our ROI analysis weighs the investment, and our look at combustion analysis training covers ways to build the underlying skills. To check your readiness against realistic questions, visit our practice test site.
Frequently Asked Questions
No weights were published in the sources reviewed. The eight phrases come from the catalog's examination description as unweighted topics, so avoid study plans that assume fixed percentages for any domain.
The catalog lists carbon monoxide safety, carbon monoxide general knowledge, and a final standalone carbon monoxide entry. The reason for the repetition is not explained, so prepare thoroughly across sources, measurement, interpretation, and safety response.
The issuer's Professional page and catalog specify 100 questions in a closed-book written format, using multiple choice. An undated training page mentions 50 questions, but the exam-specific sources support 100.
You need at least two years of verified field experience and the separate Principles of Electrical and Refrigeration Theory CORE examination. Passing candidates receive a Certificate of Achievement.
Not necessarily. The catalog lists Retail $130, Online Exam $40, and Paper Exam $50 as distinct price labels, not interchangeable totals. The CORE prerequisite and preparation materials are separate, so confirm your full cost with an approved proctor.