- NRT Exam Structure at a Glance
- All 11 NRT Content Domains Explained
- Domain Weights and Testing Strategy
- High-Priority Domains: Where the Points Are
- Medium-Priority Domains: Solid Secondary Focus
- Lower-Weight Domains: Don't Ignore Them
- How to Sequence Your Domain Study
- Leveraging Open-Book Format Across Domains
- Frequently Asked Questions
- The NRT covers exactly 11 content domains across 55 multiple-choice questions; you need 40 correct to pass.
- Air Leakage (Domain 8) carries the highest weight at 10.7% - roughly 6 questions on the actual exam.
- Five domains are tied at 9.7% each: Building Science, Insulation, HVAC, Conditioned Air Distribution, and RESNET Rating System.
- The exam is open-book; knowing where to find answers quickly is as important as memorization.
NRT Exam Structure at a Glance
The RESNET National Rater Test (NRT) is the standardized knowledge exam that sits at the heart of the HERS Rater certification pathway. Administered online through RESNET-accredited Rater Training Providers, the exam costs $125, presents 55 multiple-choice questions, and gives candidates 2 hours to complete it. A passing score requires getting at least 40 questions correct - that's a 72.7% threshold.
One of the most important structural facts: the NRT is an open-book exam. You can reference materials during the test, which fundamentally changes how you should prepare. Rather than pure memorization, the goal is deep enough understanding to apply concepts quickly while being able to look up specific code values, table entries, or thresholds efficiently.
Results are provided immediately after submission. If you don't pass, the retake waiting periods escalate: 7 days after a first failure, 14 days after a second, and 45 days after a third. That escalating timeline is one of the strongest arguments for thorough domain-by-domain preparation before sitting for the first time.
For a broader look at what makes this exam challenging, see our guide on How Hard Is the NRT Exam? Complete Difficulty Guide 2026.
All 11 NRT Content Domains Explained
The NRT content outline organizes the exam's 55 questions into 11 named domains. Below is a complete summary of each domain, its official weight, and the core competencies it tests.
Domain 1: General (7.7%)
Covers foundational knowledge that underpins the entire HERS rating process - terminology, the role of the HERS Rater, RESNET standards structure, and documentation requirements.
- RESNET definitions and standard hierarchy
- Rater roles, responsibilities, and ethics
- Rating documentation and report requirements
Domain 2: Health and Safety (10.0%)
One of the highest-weighted domains, covering combustion safety testing, carbon monoxide risks, pressure diagnostics, and protocols that protect occupant health during and after rating inspections.
- Combustion appliance zone (CAZ) testing procedures
- Carbon monoxide and backdrafting risks
- Pressure differential measurements and thresholds
- Moisture, mold, and indoor air quality considerations
Domain 3: Building Science Topics (9.7%)
Tests the physical principles that explain how heat, moisture, and air move through building assemblies - the theoretical foundation for almost every other domain.
- Heat transfer modes: conduction, convection, radiation
- Psychrometrics and moisture dynamics
- Stack effect, wind effect, and mechanical pressure drivers
- Thermal bridging and R-value vs. U-factor relationships
Domain 4: Insulation (9.7%)
Covers how insulation is graded, installed, and verified - including RESNET Grade I, II, and III definitions and common installation defects that affect the HERS score.
- Insulation grades and grading criteria
- R-value requirements by assembly type and climate zone
- Common defects: voids, compression, gaps, and bypasses
- Insulation types: batts, blown, rigid, spray foam
Domain 5: Heating and Cooling Systems (9.7%)
Addresses HVAC equipment ratings, efficiency metrics (AFUE, SEER, HSPF, COP), and how system performance data is entered into rating software.
- Efficiency ratings by equipment type
- Default vs. confirmed efficiency values in HERS software
- Equipment age, capacity, and fuel type documentation
- Heat pumps, furnaces, boilers, and packaged systems
Domain 6: Domestic Water Heating Systems (7.7%)
Focuses on water heater types, efficiency factors (EF, UEF), pipe insulation requirements, and how water heating contributes to the overall HERS Index.
- Storage, tankless, heat pump, and solar water heaters
- Energy Factor (EF) and Uniform Energy Factor (UEF)
- Hot water distribution system types and losses
Domain 7: Appliances and Lighting (7.0%)
The lightest-weighted domain. Covers how rated appliances (refrigerators, dishwashers, clothes washers/dryers) and lighting types are accounted for in the HERS rating model.
- ENERGY STAR appliance credits and defaults
- Lighting types and their impact on internal gains
- How appliances are documented in rating software
Domain 8: Air Leakage (10.7%)
The single highest-weighted domain on the NRT. Covers blower door testing procedures, ACH50 and ACHnatural calculations, and how envelope air leakage is measured, reported, and modeled.
- Blower door setup, depressurization, and test protocols
- CFM50, ACH50, and equivalent leakage area calculations
- Air sealing locations and common leakage pathways
- Compliance thresholds and how results feed into the HERS Index
Domain 9: Conditioned Air Distribution Systems (9.7%)
Covers duct leakage testing (total duct leakage, duct leakage to outside), duct location, insulation levels, and how distribution efficiency is modeled in the rating.
- Duct blaster testing setup and procedures
- Leakage metrics: CFM25 total and CFM25 to outside
- Duct insulation R-value requirements by location
- Sealed vs. leaky duct system comparisons
Domain 10: Ventilation (8.7%)
Addresses mechanical ventilation requirements, ASHRAE 62.2 protocols, and how ventilation rates are verified and entered into the rating model.
- ASHRAE 62.2 ventilation rate calculations
- Supply, exhaust, balanced, and energy-recovery ventilation systems
- Fan flow measurement methods and verification
- Infiltration credit and whole-house ventilation interaction
Domain 11: RESNET Rating System (9.7%)
Tests how the HERS Index is calculated, how the reference home is constructed, and how individual components roll up into a final HERS score.
- HERS Index reference home methodology
- How each domain's inputs affect the final HERS score
- Rating software inputs, outputs, and verification steps
- RESNET standards hierarchy and updates
For deep-dive coverage of individual domains, explore our dedicated study guides: NRT Domain 2: Health and Safety (10.0%) - Complete Study Guide 2026 and NRT Domain 8: Air Leakage are particularly high-value starting points given their exam weight.
Domain Weights and Testing Strategy
Because the NRT contains exactly 55 questions and each domain has a stated percentage weight, you can estimate the approximate number of questions per domain. This isn't a guarantee of exact question distribution, but it gives you a practical prioritization framework.
| Domain | Weight | Approx. Questions | Priority Tier |
|---|---|---|---|
| Domain 8: Air Leakage | 10.7% | ~6 | Tier 1 - Highest |
| Domain 2: Health and Safety | 10.0% | ~6 | Tier 1 - Highest |
| Domain 3: Building Science Topics | 9.7% | ~5 | Tier 2 - High |
| Domain 4: Insulation | 9.7% | ~5 | Tier 2 - High |
| Domain 5: Heating and Cooling Systems | 9.7% | ~5 | Tier 2 - High |
| Domain 9: Conditioned Air Distribution Systems | 9.7% | ~5 | Tier 2 - High |
| Domain 11: RESNET Rating System | 9.7% | ~5 | Tier 2 - High |
| Domain 10: Ventilation | 8.7% | ~5 | Tier 2 - High |
| Domain 1: General | 7.7% | ~4 | Tier 3 - Standard |
| Domain 6: Domestic Water Heating Systems | 7.7% | ~4 | Tier 3 - Standard |
| Domain 7: Appliances and Lighting | 7.0% | ~4 | Tier 3 - Standard |
Key Takeaway
The five Tier 2 domains each contribute the same number of questions. Mastering all five equally - rather than obsessing over one - is the most efficient path to clearing the 40-question threshold.
High-Priority Domains: Where the Points Are
Domain 8: Air Leakage - The Single Biggest Domain
At 10.7%, Air Leakage is the NRT's most heavily weighted content area. Questions in this domain test both procedural knowledge (how to set up and conduct a blower door test) and computational understanding (converting CFM50 to ACH50, calculating natural air change rates, determining compliance with code thresholds). Candidates who can fluently work through air leakage calculations - and know where to find conversion factors quickly in their reference materials - have a meaningful advantage. See our individual domain guides for focused preparation on each area.
Domain 2: Health and Safety - High Stakes, High Weight
Health and Safety carries 10.0% of the exam and reflects real-world liability for Raters. Combustion safety testing - particularly CAZ (Combustion Appliance Zone) depressurization testing - is a cornerstone topic. Questions often involve interpreting pressure measurements, identifying backdrafting risks, and determining when a home fails safety thresholds. This domain rewards candidates who understand the "why" behind each protocol, not just the steps.
Medium-Priority Domains: Solid Secondary Focus
Five domains are tied at 9.7% each, and a sixth (Ventilation at 8.7%) is close behind. These six domains collectively account for approximately 57.2% of the exam. No single one of them will make or break your score, but collectively they represent the bulk of the test.
Building Science (Domain 3) as the Foundation
Building Science deserves early attention in your study schedule because its concepts underpin virtually every other domain. If you understand heat transfer, moisture dynamics, and pressure relationships, questions in Insulation, HVAC, Air Leakage, and Ventilation become significantly more intuitive. Study this domain first, not just for its own 9.7% weight but for the multiplier effect it has on your comprehension elsewhere. Explore our NRT Domain 3: Building Science Topics (9.7%) - Complete Study Guide 2026 for full coverage.
RESNET Rating System (Domain 11) - The Integration Domain
Domain 11 tests how all other inputs combine into a HERS Index. Questions here often require understanding the reference home construction methodology and how changes to individual components (envelope, HVAC, water heating) shift the final score. Candidates who study this domain last - after absorbing the others - often find it the most logical to master because it synthesizes everything else.
Conditioned Air Distribution (Domain 9) - The Sister Domain to Air Leakage
Domain 9 mirrors Domain 8 in several ways: both involve diagnostic testing (duct blaster vs. blower door), both produce leakage metrics that feed directly into the HERS model, and both require understanding pressure relationships. Candidates who struggle with Domain 8 often struggle here too - and vice versa. Study these domains together for efficiency. See our NRT Domain 5: Heating and Cooling Systems (9.7%) - Complete Study Guide 2026 for HVAC-specific preparation.
Lower-Weight Domains: Don't Ignore Them
Domains 1, 6, and 7 carry 7.7%, 7.7%, and 7.0% respectively. Together they represent roughly 22.4% of the exam - that's approximately 12 questions. You cannot afford to skip them. At the 40/55 passing threshold, every question counts.
Domain 1 (General) is often underestimated. Its questions about RESNET standard structure, Rater roles, and documentation requirements are straightforward if you've reviewed the relevant RESNET standards - but easy to miss if you haven't. Domain 7 (Appliances and Lighting) is the lightest domain but covers material that's quick to learn, making it a good efficiency play late in your prep cycle. Dive into the details with our NRT Domain 7: Appliances and Lighting (7.0%) - Complete Study Guide 2026.
How to Sequence Your Domain Study
Given the domain weights and conceptual relationships, here is a research-backed sequencing approach. This is not a generic weekly template - each phase maps directly to specific NRT content logic.
Foundation: Domain 3 (Building Science) + Domain 1 (General)
- Master heat transfer principles, psychrometrics, and pressure drivers - these will accelerate comprehension in every subsequent domain
- Review RESNET standards structure, Rater role definitions, and documentation requirements for Domain 1
- Take a full-length NRT practice test at baseline to identify weakest domains before deep study
Testing Domains: Domains 8 and 9 (Air Leakage + Conditioned Air Distribution)
- Study blower door and duct blaster testing protocols together - they share diagnostic logic
- Practice CFM50-to-ACH50 conversions and duct leakage metric calculations until they're automatic
- Build your reference material tab/bookmark system for quick lookup during the open-book exam
Systems: Domains 2, 4, and 5 (Health/Safety, Insulation, HVAC)
- Focus CAZ testing procedures and combustion safety thresholds for Domain 2
- Study RESNET insulation grading criteria (Grade I, II, III) and common installation defects for Domain 4
- Review efficiency metric definitions (AFUE, SEER2, HSPF2, COP) and default vs. confirmed values for Domain 5
Integration: Domains 6, 7, 10, and 11 + Full Review
- Complete Domains 6 (Water Heating), 7 (Appliances/Lighting), and 10 (Ventilation) - focus on ASHRAE 62.2 calculation logic for Domain 10
- Study Domain 11 (RESNET Rating System) last, since it synthesizes all prior domains into the HERS Index model
- Take two additional full-length practice exams and review every missed question by domain
For a complete preparation roadmap beyond domain sequencing, see our NRT Study Guide 2026: How to Pass on Your First Attempt.
Leveraging Open-Book Format Across Domains
The NRT's open-book format is both an advantage and a trap. Candidates who over-rely on looking things up often run out of the 2-hour time limit. The optimal strategy differs by domain type.
Calculation-heavy domains (Air Leakage, Conditioned Air Distribution, Building Science): Know the formulas conceptually but have a cheat sheet with conversion factors and threshold values ready. You shouldn't be deriving CFM50-to-ACH50 conversions from scratch under time pressure.
Protocol-heavy domains (Health and Safety, Ventilation): Understand the sequence and logic of each test procedure well enough to answer without looking up. Use reference materials only to confirm specific numeric thresholds you've forgotten.
Standards-heavy domains (General, RESNET Rating System): These are the domains where tabbed references pay off most. RESNET standard section numbers, definition citations, and rating software input defaults are all legitimately look-up-able.
Practicing with realistic NRT practice questions under timed conditions - with your reference materials present - is the only way to calibrate how long look-ups actually take and where you need deeper memorization.
Key Takeaway
Open-book doesn't mean open-ended. Aim to answer at least 70% of questions from knowledge, reserving reference lookups for specific numeric thresholds you know exist but need to confirm.
Understanding the full domain breakdown is just one piece of exam preparation. For context on the broader certification investment, our NRT Certification Cost 2026: Complete Pricing Breakdown covers all fees associated with becoming a certified HERS Rater beyond just the $125 NRT exam fee.
Frequently Asked Questions
The NRT has 55 total questions distributed across 11 domains according to their stated percentage weights. Domain 8 (Air Leakage) at 10.7% yields approximately 6 questions, while Domain 7 (Appliances and Lighting) at 7.0% yields approximately 4. Exact question counts per domain can vary slightly, but the percentages give you a reliable planning framework.
Candidates with limited field experience often find Domain 8 (Air Leakage) and Domain 9 (Conditioned Air Distribution) most challenging because both require procedural knowledge of diagnostic testing and comfort with pressure-based calculations. Domain 2 (Health and Safety) can also be difficult due to the specificity of CAZ testing thresholds and pressure differential criteria.
Not fully, but deep conceptual understanding is still essential. Open-book access helps with specific numbers and table lookups, but you won't have time to research unfamiliar concepts from scratch within the 2-hour window. Aim to understand each domain well enough to answer most questions without references, using your materials only to verify specific values.
No. Even if you scored perfectly on the two highest domains (Air Leakage and Health and Safety), those would account for only about 12 questions - far short of the 40 needed to pass. All 11 domains contribute to your total, and the five mid-weight domains at 9.7% each collectively represent the largest portion of the exam.
Study duration varies by background. Candidates already working in building science or HVAC may need only a few weeks to fill gaps in domain-specific knowledge. Those newer to the field typically benefit from four to six weeks of structured domain-by-domain preparation. The four-week sequencing framework above is a reasonable starting point for most candidates.
Ready to Start Practicing?
Now that you understand all 11 NRT domains and how they're weighted, put your knowledge to the test. Our practice exams are built to mirror the real NRT's domain distribution - so you can identify gaps, build confidence, and walk into exam day prepared to clear 40 questions.
Start Free Practice Test