Common COMcheck Mistakes and How to Fix ThemCOMcheck is a widely used compliance software for demonstrating that commercial buildings meet energy code requirements. It simplifies the compliance process, but many users — especially first-timers — make recurring mistakes that can lead to failed inspections, wasted time, or inaccurate results. This article covers the most common COMcheck mistakes, explains why they matter, and provides clear, actionable fixes so your project stays on track.
1) Choosing the Wrong Code, Year, or Jurisdiction
Why it matters
- Using the incorrect code version or jurisdiction can produce a noncompliant report even if your inputs match the building’s design. Energy codes change frequently; jurisdictions may adopt different versions or local amendments.
Common errors
- Selecting a national code year (e.g., ASHRAE 90.1-2019) while the project requires a local amended version.
- Picking the wrong compliance path (e.g., selecting Prescriptive instead of Trade-off or Performance).
How to fix it
- Verify the adopted code and edition with the local building department before starting. Confirm whether the jurisdiction uses the IECC, ASHRAE 90.1, or a local standard and whether any amendments apply.
- In COMcheck, double-check the selected code year and jurisdiction dropdown. If a local amendment isn’t listed, consult the authority having jurisdiction (AHJ) and document the applicable rules in your submittal.
2) Incorrect Building Type or Space Inputs
Why it matters
- COMcheck’s defaults and compliance checks depend on the specified building type and space definitions. Mislabeling spaces can yield incorrect lighting, HVAC, or envelope requirements.
Common errors
- Grouping multiple distinct spaces under one generic space type (e.g., labeling a retail area and a storage room both as “Office”).
- Using gross building area instead of conditioned floor area for certain calculations.
How to fix it
- Break the project into accurate, discrete space types that reflect actual use, schedules, and internal loads.
- Use conditioned floor area where required; check COMcheck’s help for definitions and how it treats semi-conditioned spaces.
- When in doubt, attach explanatory notes or a space-by-space matrix to the submittal to clarify assumptions.
3) Misreporting Envelope Assemblies (U-Factors, SHGC, and Areas)
Why it matters
- Errors in window U-factors, SHGC, wall/Roof R-values, and area inputs directly affect envelope compliance. Small mistakes often have outsized impacts.
Common errors
- Entering gross window area instead of glazed area or vice versa.
- Confusing R-values with RSI or entering U-factor where R-value is required.
- Forgetting to include framing factors or thermal breaks.
How to fix it
- Measure and enter the total glazed area and the correct assembly areas separately (walls, roofs, fenestration).
- Use manufacturer data for U-factors and SHGC; when using default values, note the source.
- Convert units carefully: U = 1/R (ensure units match — ft²·°F·hr/BTU vs. SI).
- For complex assemblies, include a short calculation worksheet in the submittal showing how values were derived.
4) Lighting Power Density (LPD) Mistakes
Why it matters
- Lighting power allowances often determine pass/fail for many projects, and LPD rules vary by space type and control strategies.
Common errors
- Applying the wrong LPD allowance (e.g., using whole-building LPD for a heterogeneous space).
- Omitting exterior lighting, emergency lighting, or incorrectly modeling controls (daylight dimming, occupancy sensors).
How to fix it
- Assign correct LPDs for each space type. If using the space-by-space method, calculate and enter each space’s wattage separately.
- Include exterior lighting and explicitly note which exemptions or control credits are applied.
- Model controls accurately: specify controlled zones, daylight sensor placement, and control types (e.g., stepped vs. continuous dimming).
5) HVAC System Selection and Efficiency Inputs
Why it matters
- HVAC equipment efficiencies, system types, and control strategies heavily influence energy compliance. Mis-specifying equipment or omitting controls can invalidate results.
Common errors
- Picking an incorrect system type (e.g., single-zone packaged instead of VAV).
- Entering nameplate efficiencies improperly (e.g., gross vs. net, rated conditions vs. part-load).
- Failing to include economizers, variable-speed drives, or ventilation controls.
How to fix it
- Match the modeled HVAC system to the design documents and equipment schedules.
- Use realistic, tested efficiency values from AHRI or manufacturer data, and note whether values are rated or tested.
- Model controls and efficiency-enhancing features explicitly; if using default or baseline allowances, document the rationale.
6) Improper Use of Compliance Paths (Prescriptive vs. Performance/Trade-off)
Why it matters
- Each path has different inputs, constraints, and benefits. Choosing the wrong path or mixing methods improperly leads to errors.
Common errors
- Attempting to mix prescriptive elements with performance trade-offs in ways not allowed by the chosen code.
- Running a performance path but leaving out mandatory prescriptive requirements that must still be met.
How to fix it
- Read the applicable code’s rules for allowable combinations. COMcheck usually enforces path restrictions but verify manually.
- If using Performance, ensure mandatory prescriptive provisions (like controls or certain envelope minima) are still satisfied.
- Keep separate documentation for prescriptive items and performance trade-offs.
7) Unit and Conversion Errors
Why it matters
- COMcheck accepts inputs in U.S. customary or SI units. Unit mistakes produce incorrect results that are hard to trace.
Common errors
- Entering SI values into a field expecting IP units without converting.
- Misunderstanding area units (ft² vs. m²) or heat transfer units (Btu/hr·ft²·°F vs. W/m²·K).
How to fix it
- Set COMcheck to the desired unit system at the start and stick to it.
- Use a reliable converter and double-check conversions for U-factors, areas, and power ratings.
- Where possible, copy values directly from manufacturer datasheets that list the same units.
8) Overlooking Envelope Thermal Bridging and Framing Fractions
Why it matters
- Ignoring framing fractions, edge thermal effects, or thermal bridges can make an assembly perform worse than modeled, causing noncompliance during field verification.
Common errors
- Using idealized R-values without accounting for continuous framing or thermal breaks.
- Not including area reductions for framing when calculating effective R-values.
How to fix it
- Apply framing fractions where applicable or use adjusted U-factors that account for framing.
- For metal-framed walls/roofs, include corrections for thermal bridging or use manufacturer-adjusted U-values.
- Document assumptions and calculations in the submittal for inspector review.
9) Incomplete or Inaccurate Supporting Documentation
Why it matters
- A COMcheck report alone may not satisfy inspectors — they expect supporting documentation (schedules, calculations, product cut sheets).
Common errors
- Submitting COMcheck without equipment schedules, lighting cut sheets, or glazed product data.
- Failing to tie COMcheck inputs to contract drawings or specifications.
How to fix it
- Include equipment schedules, lighting fixture cut sheets, glazing NFRC/SHGC/U-factor data, and any calculation worksheets used.
- Add a cross-reference table linking COMcheck inputs to drawing sheet numbers or spec sections.
10) Not Preparing for Field Verification and Testing
Why it matters
- Inspectors perform field verification; differences between the built project and the COMcheck model can cause failures.
Common errors
- Assuming modeled controls, sensor locations, or commissioning steps will be implemented without coordination.
- Not scheduling testing for building envelope, HVAC commissioning, or lighting controls.
How to fix it
- Coordinate with contractors and commissioning agents to ensure installed systems match modeled controls and equipment.
- Keep an “as-built” COMcheck and update the report if changes occur during construction.
- Prepare checklists and measurement records (sensor locations, commissioning reports, equipment nameplates).
Quick troubleshooting checklist (short)
- Confirm code year and jurisdiction.
- Break project into correct space types and areas.
- Verify U-factors/SHGC and R-values against manufacturer data.
- Accurately model lighting and controls per space.
- Match HVAC system type and efficiencies to design docs.
- Use correct units and conversions.
- Attach supporting documents and calculations.
- Maintain an as-built COMcheck for field verification.
If you want, I can review a COMcheck report or your project spreadsheet and flag likely issues — upload the files or paste the key inputs.
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