Rescheck, Comcheck, and Manual J/S Reports
The Complete Guide to Building Energy Code Compliance
Everything builders, architects, homeowners, designers, engineers, and contractors need to know about REScheck, Manual J, Manual S, COMcheck, IECC requirements, and avoiding permit delays.
Last updated: October 2026 | By Brad Buzzell, M.Ed., RESNET-certified HERS Rater, Certified Energy Raters, LLC
Executive Summary
Building energy code compliance is the process of proving, before and during construction, that a building's insulation, windows, air sealing, ductwork, mechanical equipment, and lighting meet the minimum efficiency standards set by the International Energy Conservation Code (IECC) or, for many commercial buildings, ASHRAE 90.1. Residential compliance is most often documented with a REScheck report; commercial compliance with COMcheck; correct HVAC design with a Manual J load calculation and Manual S equipment selection. This guide explains what each of these documents does, why energy code review is the most common source of permit delay, and how to get every one of these reports right the first time.
Quick Answer: REScheck proves a home's building envelope (insulation, windows, air sealing) meets the IECC. Manual J calculates how much heating and cooling a building actually needs. Manual S selects HVAC equipment that matches that calculated load. COMcheck is the commercial equivalent of REScheck, covering envelope, lighting, and mechanical systems for commercial buildings. Most residential permits require REScheck plus Manual J/Manual S; most commercial permits require COMcheck.
Key Takeaways
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Energy code compliance is proven with different documents depending on building type: REScheck for most homes, COMcheck for commercial buildings, and Manual J/Manual S for HVAC design on both.
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Most permit delays tied to energy code happen because compliance documents are prepared after design instead of alongside it.
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REScheck and COMcheck prove the building envelope meets code. Manual J and Manual S are entirely separate calculations that size HVAC equipment correctly — a passing envelope report says nothing about equipment size.
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Window U-factor is the single most common cause of REScheck and COMcheck rejection.
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Climate zone, assigned by county, drives nearly every numeric requirement in the code — R-values, U-factors, SHGC limits, and lighting power density all vary by zone.
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Commercial buildings may need to comply under the IECC Commercial Provisions or ASHRAE 90.1, depending on jurisdiction, and the correct path should be confirmed before design, not after.
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The single most reliable way to prevent an energy-code-driven permit delay is to run these reports during design development, before materials are ordered and construction documents are finalized.
Introduction: Why Energy Code Compliance Decides Whether Your Permit Moves or Stalls
A building permit rarely gets rejected because of framing, plumbing, or electrical layout. Those trades are familiar, predictable, and reviewed the same way in almost every jurisdiction. Energy code compliance is different. It is one of the most common reasons residential and commercial permits get bounced back for correction, and in nearly every case, it is avoidable.
Every state that has adopted the International Energy Conservation Code (IECC) — and virtually all of them have adopted some version of it — requires proof, before a single stud goes up, that the proposed building will meet minimum energy efficiency standards. That proof takes different forms depending on the building: a REScheck report for most homes, a COMcheck report for commercial and many multifamily buildings, and a Manual J load calculation paired with a Manual S equipment selection wherever HVAC design is part of the permit package.
The problem is that most builders, and even many designers, treat these steps as paperwork to file after the design is finished rather than design constraints to plan around from day one. That single decision — treating energy code as an afterthought instead of a design input — is responsible for more permit delays than any other single factor in construction today.
This guide is built to be the single resource a builder, architect, homeowner, HVAC contractor, permit expediter, or code official needs to understand every part of this process: what each report does, why permit delays happen, what the IECC actually requires, why window U-factor causes so many rejections, and how REScheck, Manual J, Manual S, and COMcheck relate to — and differ from — one another.
What Is Building Energy Code Compliance?
Building energy code compliance is the documented demonstration that a building's design and construction meet the minimum energy efficiency requirements adopted by the jurisdiction where it is built. It is not a single document or a single test — it is a category that includes several distinct deliverables, each covering a different part of the building.
Important: "Energy code compliance" is often used loosely to mean "the REScheck report," but the term actually covers building envelope compliance (REScheck/COMcheck), mechanical load calculations (Manual J), equipment selection (Manual S), duct design (Manual D), air sealing verification (blower-door testing), and duct leakage testing — all of which may be required on the same project.
At its core, energy code compliance answers four separate questions:
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Does the building envelope meet code? — Answered by REScheck (residential) or COMcheck (commercial).
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How much heating and cooling does the building need? — Answered by Manual J.
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What equipment should be installed? — Answered by Manual S.
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Is the building actually built as tight and as documented as designed? — Answered by blower-door and duct-leakage testing at inspection.
Understanding the IECC
The International Energy Conservation Code (IECC) is a model energy code published by the International Code Council (ICC) on a three-year revision cycle — the 2018, 2021, and 2024 editions are all currently in active use somewhere in the United States. States and local jurisdictions each adopt a specific edition, often with local amendments, as their legally enforceable minimum energy standard.
Did you know? The IECC is split into two largely separate sets of provisions: the Residential Provisions (covering one- and two-family dwellings and low-rise multifamily buildings) and the Commercial Provisions (covering everything else, including larger multifamily buildings). Many commercial projects can also elect to comply with ASHRAE 90.1 instead of the IECC Commercial Provisions, depending on what the jurisdiction allows.
Why code editions vary by location
Adoption is a local legislative decision, not an automatic update. A jurisdiction can legally continue enforcing the 2018 IECC years after the 2021 or 2024 edition has been published, and a neighboring county can be enforcing a newer edition at the same time. This is why confirming the exact adopted edition — and any local amendments — for the specific county or city is a non-negotiable first step on every project.
Real-world example: A regional builder using a standard floor plan across three counties in the same state assumed identical code requirements everywhere. Two counties had adopted the 2021 IECC; the third was still enforcing the 2018 IECC with a local amendment reducing the required ceiling R-value. The REScheck report built for the 2021-compliant counties was rejected in the third county because it referenced the wrong code edition entirely — not because the building was non-compliant, but because the report didn't match the adopted code.
Residential Energy Code Compliance
Residential energy code compliance applies to one- and two-family dwellings, townhouses, and (in most editions) multifamily buildings three stories or fewer. It is governed by the IECC's Residential Provisions and is documented primarily through REScheck, supported by Manual J and Manual S for HVAC design, and verified at inspection through blower-door and duct-leakage testing.
Residential compliance regulates: ceiling, wall, floor, and foundation insulation R-values; window and door U-factor and SHGC; whole-building air leakage rate; duct insulation and leakage; and, in many editions, mechanical ventilation for indoor air quality.
Commercial Energy Code Compliance
Commercial energy code compliance applies to office buildings, retail spaces, restaurants, warehouses, schools, churches, and multifamily buildings above the residential height/story threshold. It is governed by either the IECC's Commercial Provisions or ASHRAE 90.1, and is documented primarily through COMcheck.
Commercial compliance regulates the same envelope categories as residential compliance, plus two categories residential code doesn't address in the same way: lighting power density (the maximum wattage of lighting per square foot, by space type) and more detailed mechanical system efficiency and controls requirements, reflecting the larger and more complex HVAC systems typical of commercial buildings.
Expert insight: Small-to-medium commercial projects — a single-tenant retail buildout, a small office renovation, a restaurant shell — are exactly the kind of project where COMcheck's prescriptive path is most useful, since a full energy model isn't required and the prescriptive lighting and envelope tables can typically be met with standard, off-the-shelf specifications.
REScheck: The Complete Explanation
What REScheck is
REScheck is free compliance software published by the U.S. Department of Energy that verifies a residential building's envelope — insulation, windows, doors, and air sealing — meets the minimum requirements of the adopted IECC edition for its climate zone. It produces a report that plan reviewers use to confirm code compliance at permit submission.
Why REScheck exists
Before compliance software existed, plan reviewers had to manually check dozens of individual component values against code tables for every submitted design — a slow, error-prone process. REScheck standardizes this into a single calculation that either passes or fails against the applicable code requirements, giving both the design team and the reviewer a consistent, auditable result.
When REScheck is required
REScheck (or an equivalent residential energy compliance path) is required for new home construction, additions, and in many jurisdictions substantial renovations, wherever the local jurisdiction has adopted the IECC Residential Provisions. It is typically submitted alongside the rest of the construction document set at permit application.
How REScheck works
The software takes as inputs the climate zone, the proposed R-values for each envelope assembly (ceiling, wall, floor, foundation), and the U-factor and SHGC for each window and door type. It then compares the design either component-by-component against a prescriptive table (Prescriptive Path) or as a whole-building heat-loss/gain calculation (UA Trade-off / Performance Path), and outputs a pass/fail compliance certificate.
Common REScheck mistakes
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Using the wrong IECC edition or climate zone for the specific county
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Reporting window U-factor from marketing materials instead of the NFRC label
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Averaging U-factors across multiple window types instead of entering each type separately
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Missing air-sealing or duct-leakage testing documentation required by the same code edition
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A mismatch between the drawings' window schedule and the values entered into the report
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The typical REScheck review process
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Design team finalizes (or drafts) envelope specifications: insulation R-values, window/door U-factor and SHGC.
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REScheck report is generated using the correct climate zone and adopted code edition.
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Report is submitted with the rest of the construction document set at permit application.
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An energy code reviewer — sometimes a dedicated specialist separate from the general plans examiner — checks the report against the adopted code.
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At the appropriate construction stage, a blower-door test (and duct-leakage test, if applicable) verifies the building was actually built to the documented performance.
Best practice: Generate a preliminary REScheck report during schematic design — before window orders are placed — so that any gap between the proposed design and code requirements is caught while changes are still inexpensive.
Manual J: The Complete Explanation
What Manual J is
Manual J is a calculation methodology published by the Air Conditioning Contractors of America (ACCA) used to determine a building's actual heating and cooling load — how many BTUs of heating and cooling capacity the space genuinely needs, room by room. It is an entirely separate deliverable from REScheck: REScheck proves the envelope meets minimum code; Manual J calculates the real-world load that envelope produces.
Why rules of thumb fail
A widespread shortcut in residential HVAC is sizing equipment by a rule of thumb — commonly "a ton of cooling per 400–600 square feet" — without any calculation. This approach ignores window area and orientation, insulation levels, air leakage, ceiling height, local design temperatures, and internal heat gains, all of which materially change the actual load. Two identically sized homes in the same climate zone can have meaningfully different loads if one has more south-facing glass or better wall insulation than the other.
Common mistake: An HVAC contractor sizes a furnace and condenser using a square-footage rule of thumb rather than a Manual J calculation. The equipment installed is larger than the home's actual calculated load, and the home experiences short-cycling, poor humidity control, and higher energy bills — despite the building envelope having passed REScheck with no issues.
Heating load vs. cooling load calculations
Manual J calculates heating and cooling loads separately, because they respond to different variables. Heating load calculations are driven primarily by envelope heat loss at winter design temperatures — insulation, air leakage, and window U-factor dominate. Cooling load calculations add solar heat gain (driven by SHGC and window orientation), internal heat gains from occupants and appliances, and humidity/latent load considerations that don't apply to heating.
Room-by-room calculations
Manual J is performed room by room, not just for the building as a whole, because a whole-building load number doesn't tell a contractor how to size and balance the duct system or how many supply registers a given room needs. Room-by-room results feed directly into Manual D duct design, ensuring each room receives the airflow its individual load requires.
Manual J and permit requirements
Requirements vary by jurisdiction, but a Manual J calculation is frequently required by the local mechanical code or the building department's standard permit checklist — independent of whether it's explicitly cited within the energy code itself — specifically to prevent oversized or undersized HVAC equipment.
Common Manual J mistakes
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Using default or assumed insulation/air-leakage values instead of the values actually specified in the REScheck report
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Ignoring window orientation and SHGC when calculating cooling load
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Calculating only a whole-building load instead of room-by-room loads needed for proper duct design
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Using outdated or incorrect outdoor design temperatures for the specific location
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Failing to update the calculation after a late-stage design change (added windows, altered floor plan)
Manual S: The Complete Explanation
What Manual S is
Manual S is the ACCA methodology used to select specific HVAC equipment that matches the load calculated in Manual J. Where Manual J answers "how much heating and cooling capacity does this building need," Manual S answers "which specific piece of equipment, at its actual rated performance, correctly meets that need."
Why Manual S depends on Manual J
Manual S cannot be performed correctly without a Manual J calculation, because equipment selection is only meaningful relative to a known load. Selecting equipment without a Manual J is effectively guessing; performing Manual S is the process of translating a calculated load into an actual model number, using the manufacturer's certified performance data at the specific design conditions for that location.
Using manufacturer performance data correctly
Manual S requires using the manufacturer's extended performance data — capacity at the actual outdoor design temperature, not just the nameplate rating at standard test conditions — because a piece of equipment's real capacity changes with outdoor temperature. Selecting equipment off nameplate tonnage alone, without checking performance at the local design temperature, is one of the most common Manual S errors.
Oversized equipment: the most common and most damaging mistake
Oversized HVAC equipment is extremely common and causes a specific, predictable set of problems:
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Short cycling — the equipment reaches setpoint quickly and shuts off before completing a full dehumidification cycle
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Poor humidity control — especially in cooling mode, since dehumidification requires sustained runtime
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Reduced comfort — larger temperature swings between cycles
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Shorter equipment lifespan — more frequent starts and stops increase wear
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Higher energy costs — despite intuition suggesting "bigger is safer," oversized equipment is measurably less efficient in practice
Undersized equipment
Undersized equipment is less common but equally problematic — it runs continuously during peak load conditions and still fails to reach setpoint, producing comfort complaints during the hottest and coldest days of the year, precisely when the equipment is needed most.
Why many jurisdictions require Manual S
Jurisdictions that require Manual S alongside Manual J do so because a passing Manual J calculation, by itself, doesn't guarantee correctly sized equipment gets installed — a contractor could still select an oversized unit even with an accurate load calculation in hand. Requiring the Manual S selection documentation closes that gap by requiring the actual proposed equipment to be checked against the calculated load before permit issuance.
Warning: A common but incorrect assumption is that a passing REScheck report, combined with "a licensed HVAC contractor installing the system," is sufficient assurance of correct equipment sizing. Neither REScheck nor a contractor's license verifies equipment sizing — only a Manual J plus Manual S package does.
COMcheck: The Complete Explanation
What COMcheck is
COMcheck is free compliance software, also published by the U.S. Department of Energy, used to demonstrate that a commercial building meets the applicable commercial energy code — either the IECC Commercial Provisions or ASHRAE 90.1, depending on what the jurisdiction allows or requires. It is the commercial counterpart to REScheck.
IECC Commercial vs. ASHRAE 90.1
Many jurisdictions allow commercial projects to demonstrate compliance under either the IECC Commercial Provisions or ASHRAE 90.1 — two related but not identical standards. COMcheck supports compliance documentation under both, and the applicable choice is typically set by the adopting jurisdiction rather than left entirely to the design team, though some jurisdictions do allow the design team to choose whichever standard the project can more easily meet.
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COMcheck by building and project type
Office buildings
Typically straightforward prescriptive compliance; lighting power density and window performance are usually the driving factors.
Retail
Higher allowed lighting power density than office space in most tables, but display lighting rules can add complexity.
Restaurants
Kitchen exhaust and makeup air interact with mechanical compliance; envelope compliance is usually standard.
Warehouses
Large envelope area with typically low lighting power density; envelope insulation is often the main compliance driver.
Mixed-use buildings
May require splitting compliance documentation by space type or building section, especially where uses cross the residential/commercial threshold.
Churches and schools
Often use assembly-specific lighting power density allowances and are frequently sensitive to occupancy-based ventilation requirements.
Tenant improvements
Tenant improvement (TI) projects — build-outs within an existing shell — frequently require their own COMcheck submittal, scoped to the improved space rather than the whole building, particularly for lighting compliance. A common oversight is assuming the base building's original COMcheck approval covers a new tenant's fit-out; in most jurisdictions it does not.
Common COMcheck mistakes
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Using the wrong compliance standard (IECC Commercial vs. ASHRAE 90.1) for the jurisdiction
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Missing lighting power density calculations for a tenant improvement scope
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Incorrect space-type classification, which changes the allowed lighting power density
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Envelope U-factor and SHGC errors, identical in nature to the residential mistakes covered above
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Failing to document mechanical system efficiency and controls for larger HVAC equipment
Commercial inspections
Commercial energy code compliance is verified at inspection much like residential compliance, though the specific tests differ: envelope air sealing may be inspected visually rather than with a blower-door test at commercial scale, and lighting inspections typically verify installed fixture wattage and controls match the approved COMcheck report.
Five Costly Energy Code Mistakes Builders Make
1. Treating the energy code report as a paperwork formality instead of a design constraint
Builders often finalize floor plans, window schedules, and insulation specs, then hand the package to whoever is producing the REScheck or COMcheck report as a last step before permit submission. If the design doesn't actually meet code, the report fails, and windows already ordered, framing already drawn, and schedules already set all have to be revisited.
2. Using outdated or incorrect code editions and climate zone data
Two counties in the same state can be enforcing different IECC editions simultaneously. A report generated with the wrong code year or climate zone produces a compliant-looking result the reviewer rejects on sight.
3. Misreporting or mismatching window U-factor and SHGC values
Covered in full detail below — this single category of error is the leading cause of REScheck and COMcheck correction notices nationwide.
4. Missing or incomplete duct and envelope air-sealing documentation
Modern energy codes regulate airtightness as well as insulation levels. Builders sometimes assume meeting R-values is sufficient and are surprised when a certificate of occupancy is held up pending a blower-door or duct test that was never scheduled.
5. Confusing envelope compliance with HVAC sizing — or skipping Manual J/Manual S altogether
A REScheck or COMcheck report can pass while the HVAC contractor sizes equipment using a rule of thumb. Many jurisdictions require Manual J and Manual S as separate submittals, and builders who assume envelope compliance covers the mechanical side are frequently caught off guard by a second correction notice.
Why Permit Delays Happen
Energy code is reviewed by a specialist, not the general plans examiner
In many jurisdictions, a general plans examiner checks structural and life-safety items, while a separate energy code reviewer checks the REScheck or COMcheck submittal against the adopted code edition — often on its own timeline, resetting the clock on the entire permit.
Energy code requirements are numeric and non-negotiable
Unlike code sections that allow engineering judgment, energy code compliance is usually a pass/fail numeric comparison, leaving little room for reviewer discretion.
Small, overlooked details cause outsized delays
A missing insulation value, an incomplete window schedule, or ductwork shown without an insulation callout can invalidate an entire report, not just one line item.
Many correction cycles happen not because the building fails to meet code, but because the compliance report doesn't contain enough information for the reviewer to confirm it does. Incomplete documentation and actual non-compliance produce the same rejection letter — but incomplete documentation is entirely preventable.
Best practice: Generate REScheck, COMcheck, or Manual J/Manual S documentation during design development — before window orders are placed, before truss packages are finalized, and before the full construction document set is submitted for permit.
Common Window U-Factor Mistakes
Window U-factor measures the rate of heat transfer through a window assembly, expressed in Btu/(hr·ft²·°F); lower is better. It is, by a wide margin, the single most common source of REScheck and COMcheck correction notices.
Mistake 1: Confusing U-factor with SHGC
The NFRC label lists both U-factor (heat loss) and Solar Heat Gain Coefficient (solar heat gain) — two different measurements that are frequently transposed or reported as one value.
Mistake 2: Using marketing U-factors instead of NFRC-certified values
Marketing materials sometimes advertise a best-case U-factor that doesn't match the specific configuration ordered. Only the NFRC label for the exact unit ordered is acceptable.
Mistake 3: Averaging U-factors across a mixed window order
Different window types in the same order often have different certified U-factors. Reporting one averaged value can mask a window type that wouldn't pass on its own.
Mistake 4: Applying the wrong climate zone's maximum U-factor
A window that easily complies in one climate zone may fail in a colder one. Reusing a window schedule across markets without rechecking it is a common source of this error.
Mistake 5: Leaving U-factor off the window schedule entirely
Reviewers frequently reject submittals where the drawings and compliance report don't independently confirm the same values.
Climate Zones Explained
The IECC divides the United States into eight climate zones (1 through 8, with moist/dry/marine subtypes in several), assigned by county based on heating and cooling degree days. Nearly every numeric requirement in the code — R-values, U-factors, SHGC limits, and commercial lighting power density — is published as a separate figure for each zone.
A climate zone is assigned by county, not by state — meaning a builder working across county lines in the same state can face two different sets of numeric requirements on projects that otherwise look identical.
Prescriptive vs. Performance Path
What Documents Are Required for Permits?
Choosing the Right Report
Which report a project needs depends on building type and scope, not on preference. As a starting framework: if the project is a one- or two-family home or a low-rise multifamily building, REScheck applies to the envelope, and Manual J/Manual S apply to the HVAC design. If the project is a commercial building, a larger multifamily building, or a tenant improvement within one, COMcheck applies. Many projects need more than one of these documents simultaneously — this is normal, not a sign that something has gone wrong.
REScheck vs. Manual J vs. Manual S vs. COMcheck
Builder Best Practices
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Confirm the adopted IECC edition, climate zone, and local amendments for the specific county before finalizing window orders or wall assemblies.
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Run a preliminary REScheck report during schematic design, not after construction documents are complete.
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Require Manual J and Manual S documentation from the HVAC contractor as a standard part of the bid package, not an afterthought.
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Keep window schedules and compliance reports in sync — update both whenever a substitution is made.
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Schedule blower-door and duct-leakage testing early enough in the schedule to allow for retesting if needed.
Architect Best Practices
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Treat envelope performance targets (R-values, U-factor, SHGC) as design inputs at schematic design, not values to reverse-engineer later.
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Coordinate window selection with the compliance path chosen (prescriptive vs. UA Trade-off) before finalizing glazing area.
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Specify NFRC-certified U-factor and SHGC values directly on the window schedule, matching the compliance report.
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Confirm which commercial standard (IECC Commercial vs. ASHRAE 90.1) governs the project before finalizing lighting design.
Homeowner Guide
If you're building or substantially renovating a home, it's reasonable to ask your builder directly whether a REScheck report, a Manual J calculation, and a Manual S equipment selection have been completed — and to ask to see the results. A REScheck pass tells you the envelope meets minimum code; it does not tell you your HVAC equipment is correctly sized. Those are two separate questions, and a diligent builder should be able to answer both.
Commercial Contractor Guide
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Confirm early whether the jurisdiction requires IECC Commercial Provisions or allows ASHRAE 90.1 compliance, since lighting and envelope tables differ between the two.
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For tenant improvement work, confirm whether a new COMcheck submittal is required for the improved space, even if the base building already has an approved report.
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Classify space types correctly on the lighting compliance worksheet — allowed lighting power density varies significantly by space type.
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Document mechanical system efficiency and controls completely; incomplete mechanical documentation is a common source of commercial correction notices.
Glossary: Key Energy Code Terms Defined
IECC (International Energy Conservation Code)
A model energy code published by the International Code Council, updated on a three-year cycle, and adopted (often with local amendments) by most U.S. states as the legal minimum energy efficiency standard for new construction.
ASHRAE 90.1
A commercial building energy standard published by ASHRAE, used as an alternative or companion compliance path to the IECC Commercial Provisions in many jurisdictions.
REScheck
Free compliance software from the U.S. Department of Energy used to demonstrate that a residential building's envelope meets the requirements of the adopted IECC edition.
COMcheck
The commercial-building counterpart to REScheck, used to demonstrate commercial energy code compliance covering envelope, lighting, and mechanical systems.
Manual J
An ACCA-published calculation methodology used to determine the precise heating and cooling load of a building, room by room, for the purpose of correctly sizing HVAC equipment.
Manual S
The ACCA methodology used to select specific HVAC equipment that matches the load calculated by Manual J, ensuring equipment capacity is neither oversized nor undersized.
Manual D
The ACCA methodology used to design residential duct systems based on the room-by-room loads calculated in Manual J.
U-factor
A measurement of the rate of heat transfer through a window, door, or skylight assembly, expressed in Btu/(hr·ft²·°F). Lower values indicate better insulating performance.
SHGC (Solar Heat Gain Coefficient)
A measurement of how much solar radiant heat passes through a window or door, expressed as a fraction between 0 and 1. Lower values block more solar heat.
Conditioned space
Any enclosed space within a building that is directly heated or cooled, or indirectly conditioned by being connected to a heated/cooled space without a thermal boundary between them.
Climate zone
One of eight IECC-defined geographic zones assigned by county, based on heating and cooling degree days. Nearly every numeric code requirement is published separately for each climate zone.
HERS Rating (Home Energy Rating System)
A scoring system, administered by RESNET-certified raters, that rates a home's energy efficiency relative to a reference home, used both voluntarily and as an alternative (ERI) compliance path.
Blower door test
A diagnostic test using a calibrated fan to measure a building's air leakage rate, verifying compliance with the code's maximum allowable air changes per hour.
Duct leakage testing
A test measuring how much conditioned air escapes a duct system, required in many code editions when ducts run through unconditioned space.
UA Trade-off
A performance-path compliance method that allows a weaker-performing component to be offset by a stronger one elsewhere in the building, as long as total heat loss/gain equals or betters a fully prescriptive design.
Lighting power density
The maximum allowed lighting wattage per square foot for a given commercial space type, regulated under COMcheck's lighting compliance path.
Frequently Asked Questions
What is REScheck?
REScheck is free compliance software published by the U.S. Department of Energy that verifies a residential building's insulation, window performance, and air sealing meet the minimum requirements of the adopted IECC edition for its climate zone.
What is COMcheck used for?
COMcheck is the commercial-building counterpart to REScheck. It demonstrates that a commercial building's envelope, lighting power density, and mechanical systems meet the applicable commercial energy code.
Do I need both REScheck and Manual J?
In most jurisdictions, yes. REScheck demonstrates the building envelope meets minimum energy code. Manual J is a separate calculation that sizes HVAC equipment correctly. Many building departments require both.
What is Manual S and why is it required alongside Manual J?
Manual S is the equipment-selection step that matches actual HVAC equipment to the load calculated by Manual J. It's required alongside Manual J because an accurate load calculation doesn't guarantee correctly sized equipment gets installed.
What is a U-factor on a window?
U-factor measures the rate of heat transfer through a window assembly, expressed in Btu/(hr·ft²·°F). Lower U-factor means better insulating performance, and the IECC caps the maximum allowable value by climate zone.
What is SHGC and how is it different from U-factor?
SHGC measures how much solar radiant heat passes through a window, while U-factor measures conductive heat loss. Both appear on the same NFRC label but govern different physical properties.
Why did my REScheck report get rejected?
Common reasons include an incorrect IECC edition or climate zone, incorrect window U-factor or SHGC values, mismatches between drawings and the compliance report, or missing air-sealing and duct-testing documentation.
Why did my COMcheck report get rejected?
Common reasons include using the wrong compliance standard for the jurisdiction, incorrect space-type classification affecting lighting power density, and envelope U-factor or SHGC errors similar to residential submittals.
What climate zone am I in?
Climate zone is assigned by county under the IECC, based on heating and cooling degree days, ranging from Zone 1 (hot) to Zone 8 (very cold).
What IECC edition does my state use?
It depends on the state and often the specific county, since jurisdictions adopt IECC editions and local amendments on their own timeline.
What is Manual J used for?
Manual J is an ACCA calculation methodology used to determine a building's actual heating and cooling load, room by room, so HVAC equipment can be sized correctly rather than estimated with a rule of thumb.
Can oversized HVAC equipment still pass REScheck?
Yes. REScheck evaluates the building envelope, not equipment sizing. A building can have a fully compliant envelope and still have oversized HVAC equipment if Manual J and Manual S weren't performed.
What problems does oversized HVAC equipment cause?
Oversized equipment tends to short-cycle, dehumidify poorly, produce larger temperature swings, wear out faster, and use more energy than correctly sized equipment despite intuition suggesting otherwise.
What is conditioned space under the energy code?
Conditioned space is any enclosed area that is directly heated or cooled, or indirectly conditioned through an open connection to a heated or cooled space with no thermal boundary between them.
Why do window U-factor mistakes delay so many permits?
Because U-factor values are often pulled from marketing materials instead of NFRC-certified labels, averaged incorrectly across window types, or matched to the wrong climate zone.
Where do I find the certified U-factor for my windows?
The NFRC label affixed to the window, or the manufacturer's official NFRC certification documentation for the specific ordered configuration, is the only acceptable source.
What is a blower door test and is it required?
A blower door test measures a building's air leakage rate using a calibrated fan. Most current IECC editions require it to verify compliance with maximum air leakage limits.
What is duct leakage testing?
Duct leakage testing measures how much conditioned air escapes a duct system, and is required in many IECC editions when ducts run through unconditioned space.
What is the UA Trade-off method in REScheck?
UA Trade-off is a performance-path compliance option allowing a weaker component to be offset by stronger performance elsewhere, provided total building heat loss/gain equals or betters a fully prescriptive design.
What is a HERS rating and how does it relate to code compliance?
A HERS rating scores a home's efficiency relative to a reference home. In jurisdictions allowing the Energy Rating Index path, a sufficiently low HERS score can serve as an alternative to prescriptive compliance.
Does a home addition or renovation need to meet the energy code?
In most jurisdictions, yes — additions and substantial renovations typically must meet current energy code requirements for the new or altered portions, depending on local amendments and scope of work.
Who reviews energy code compliance during plan review?
In many jurisdictions, a dedicated energy code reviewer checks the REScheck or COMcheck submittal separately from the general plans examiner who checks structural and life-safety items.
Can I use the same window schedule on a repeat floor plan in a different location?
Not without rechecking it. Climate zone requirements for U-factor and SHGC vary by location, so a window schedule that complies in one zone may not comply in another.
What information does a plan reviewer need to see on a window schedule?
At minimum, the certified U-factor and SHGC for each unique window type used in the design, matching the values entered into the compliance report.
What's the difference between R-value and U-factor?
R-value measures resistance to heat flow (higher is better) and is typically used for insulation. U-factor measures the rate of heat transfer (lower is better) and is typically used for windows, doors, and skylights.
Is a Manual J calculation required by code, or is it a best practice?
Requirements vary by jurisdiction, but Manual J is frequently required by the local mechanical code or permit checklist specifically to prevent oversized or undersized HVAC equipment.
What causes the most delay: envelope compliance or mechanical compliance?
Envelope compliance issues tend to cause the earliest delays since they're reviewed at initial submission, while mechanical/Manual J issues often surface later, sometimes not until rough-in inspection.
Do local amendments override the base IECC requirements?
Yes. When a jurisdiction adopts the IECC with local amendments, the amended requirements are the legally enforceable standard, even if they differ from the unamended model code.
What is the difference between the IECC Commercial Provisions and ASHRAE 90.1?
Both are model commercial energy standards; the applicable one depends on jurisdiction adoption. COMcheck supports compliance documentation under either.
Does a commercial tenant improvement need its own COMcheck report?
Typically yes, particularly for lighting compliance, even if the base building already has an approved COMcheck report from original construction.
What is lighting power density?
Lighting power density is the maximum allowed lighting wattage per square foot for a given commercial space type, regulated under COMcheck's lighting compliance path.
How is a restaurant's energy code compliance different from an office's?
Restaurants involve kitchen exhaust and makeup air considerations that interact with mechanical compliance, while envelope and lighting compliance generally follow standard commercial pathways.
Do warehouses need to meet the same energy code as offices?
Yes, under the same commercial provisions, though warehouses typically have lower allowed lighting power density and their envelope insulation is often the main compliance driver given the large envelope area.
What is Manual D?
Manual D is the ACCA methodology for designing residential duct systems based on the room-by-room heating and cooling loads calculated in Manual J.
Why does Manual S depend on Manual J?
Manual S selects equipment relative to a known load; without a Manual J calculation, equipment selection has no accurate load to be matched against.
What manufacturer data does Manual S require?
Manual S requires extended performance data showing equipment capacity at the actual outdoor design temperature for the project location, not just the nameplate rating at standard test conditions.
Can undersized HVAC equipment pass inspection?
It can pass envelope inspection, since REScheck doesn't evaluate equipment sizing, but undersized equipment typically produces comfort complaints during peak load conditions that a Manual J/Manual S package is designed to prevent.
What is the Prescriptive Path in the IECC?
The Prescriptive Path requires every building component to independently meet a fixed minimum or maximum table value for its climate zone, without trade-offs between components.
What is the Performance Path in the IECC?
The Performance Path models the building as a whole system, allowing a weaker-performing component to be offset by a stronger one elsewhere, as long as total performance equals or exceeds the prescriptive standard.
Does multifamily housing use REScheck or COMcheck?
It depends on building height and story count. Low-rise multifamily buildings often use REScheck, while mid- and high-rise multifamily buildings typically fall under commercial provisions and use COMcheck.
What is the fastest way to avoid an energy-code-related permit delay?
Generate REScheck, COMcheck, or Manual J/Manual S documentation during design development, before materials are ordered and before the final construction document set is submitted for permit.
Who performs a HERS rating?
A HERS rating is performed by a RESNET-certified Home Energy Rater, using standardized inspection and testing protocols to score a home's efficiency relative to a reference home.
Conclusion: Build the Compliance Check Into the Design, Not the Punch List
Every mistake covered in this guide traces back to the same root cause: energy code compliance treated as documentation to produce after the design is finished, instead of a set of design constraints applied from the first set of drawings. The IECC's numeric requirements — insulation R-values, window U-factor and SHGC limits, air sealing rates, duct performance, lighting power density — are all known quantities the moment a project's address, climate zone, and building type are established. There's no reason any of them should be a surprise at plan review.
The builders, architects, and contractors who avoid permit delays consistently share one habit: they confirm the applicable code edition, climate zone, and local amendments before finalizing window orders and wall assemblies, and they generate REScheck, COMcheck, Manual J, and Manual S documentation as part of design development rather than as a final step before submission. That single shift in sequencing — compliance first, documentation second — is what separates projects that move smoothly through plan review from projects stuck in repeated correction cycles.
For builders, architects, and design teams who want a second set of eyes on that process — whether it's verifying the correct climate zone and code edition for a specific county, checking a window schedule for U-factor and SHGC accuracy, or producing a full REScheck, COMcheck, or Manual J/Manual S package — RescheckReview.com and Certified Energy Raters, LLC provide RESNET-certified energy code compliance review nationwide, built specifically around catching these issues before they reach a plan reviewer's desk.
Need a compliance report checked before it goes to permit?
Certified Energy Raters, LLC provides REScheck, COMcheck, and Manual J/Manual S reports and reviews for builders, architects, and design-build firms nationwide. Visit RescheckReview.com for state-specific requirement guides and service details.