Energy calculation

An energy calculation demonstrates that a building meets the adopted energy code. It accounts for insulation levels, window performance, air leakage, duct location, and the efficiency of heating and cooling equipment, then shows the result is at or better than what the code requires.

Where it applies in the lifecycle

• Preparation. The calculation is run against the design and included in the package.
• Plan review. An energy reviewer checks that the inputs match the drawings. Mismatches between the calculation and the plans are the single most common energy comment.
• Inspections. Insulation and duct inspections verify that what was installed matches what the calculation assumed.

Common forms

• REScheck and COMcheck, the free federal compliance tools
• State-specific forms, such as Florida's energy code compliance forms
• Manual J, Manual S, and Manual D for HVAC load, equipment selection, and duct design, often required alongside the envelope calculation

Where it goes wrong

The calculation is only as good as its inputs, and it is usually run before the design is final. When window sizes change, when the wall assembly changes, or when a different HVAC unit is substituted, the calculation stops matching the drawings. Reviewers check for exactly this, and it is worth re-running the numbers after any design change rather than at the end.