Design Sanity Checker

Check design numbers against rule-of-thumb ranges for the building type.

Your Design Numbers

Sanity Check Results

Inputs, results, and method — as an Excel workbook or plain CSV.

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ℹ️ About This Tool

The Design Sanity Checker is a fast gut-check for HVAC sizing numbers. Enter floor area, building type, cooling tons, heating MBH, supply CFM, and optionally chilled-water GPM, and it computes the intensity ratios engineers use to judge whether a design is in the right ballpark — then flags each one green, amber, or red against typical ranges.

It is meant to catch the obvious mistakes — a misplaced decimal, a transposed digit, the wrong unit — before they make it onto a schedule. It is a screening aid, not a load calculation; benchmark ranges vary widely with climate, glazing, occupancy, and process loads.

🔬 Formula & Method

Area per tonft²/ton = floor area ÷ cooling tons
Airflow densityCFM/ft² = supply CFM ÷ floor area
Heating densityBTU/hr/ft² = (MBH × 1,000) ÷ floor area
Coil airflowCFM/ton = supply CFM ÷ cooling tons
Chilled waterGPM/ton = chilled-water GPM ÷ cooling tons  ·  implied ΔT = 24 ÷ GPM/ton

Each ratio is compared to a typical range for the chosen building type. In range passes. For ft²/ton, CFM/ft² and heating BTU/hr·ft², the warning zone runs from 0.6× the low end to 1.5× the high end of the load intensity (for ft²/ton that is low ÷ 1.5 to high ÷ 0.6); beyond it fails, high or low. CFM/ton passes at 350–450 and warns at 250–600; GPM/ton passes at 1.5–3.5 (16–7°F ΔT). The ft²/ton, CFM/ft², heating and CFM/ton bands are the ones the AIM Works app uses to benchmark a load calc (restaurants are banded separately here). They are common rule-of-thumb practice, not code minimums, and never replace a room-by-room load calculation. CFM figures assume sea-level air; at 5,000 ft the same load needs about 20% more CFM.

❓ Frequently Asked Questions

What does the Design Sanity Checker actually check?
It computes four core intensity metrics from your numbers and compares each to a typical range for the building type: square feet per ton of cooling, CFM per square foot, heating BTU/hr per square foot, and CFM per ton. If you enter chilled-water GPM, it also checks GPM per ton and shows the chilled-water delta-T it implies. Each metric gets a pass, warn, or fail flag so you can spot an outlier before it reaches a drawing; a ratio whose inputs are blank is shown as not checked.
How are the pass, warn, and fail flags decided?
A value inside the typical range for the selected building type passes. A value moderately outside it warns, and a value far outside it in either direction fails: for the intensity checks, the warning zone runs from 0.6 times the low end to 1.5 times the high end of the load intensity, the same grading the AIM Works app uses. CFM per ton passes at 350 to 450 and warns from 250 to 600. The bands are intentionally broad; a flag is a prompt to double-check, not proof of an error.
What is a typical square feet per ton for an office?
For modern offices the tool uses 300 to 450 square feet per ton, the same band the AIM Works app benchmarks against. Denser loads run lower: hospitals 150 to 350, labs 100 to 350, restaurants 100 to 200. Warehouses run much higher, 400 to 2,500. These are screening ranges; an actual load calculation can land outside them for a specific building with unusual glazing, occupancy, or process loads.
Can I rely on these benchmarks for final design?
No. Rule-of-thumb ratios are a sanity check, not a design method. They catch gross errors such as a transposed digit or wrong unit, but a real project needs a room-by-room load calculation following ASHRAE methods. Use the checker to validate that your detailed results are in a believable range.

🔗 Related Tools

Rule-of-Thumb Checker Quick Load Estimator CFM / Tons / BTU Converter GPM / Tons / ΔT
AIM Works · launches Oct 15, 2026

Connect the calculation to the rest of the project.

AIM Works brings peak loads, ASHRAE 62.1 ventilation, equipment and plant sizing, compliance checks, Design Review, and engineering deliverables into one connected mechanical design workspace.

  • Peak loads (RTS or CLTD/CLF) and ASHRAE 62.1-2019 ventilation
  • Equipment and plant sizing against ASHRAE 90.1-2022 efficiency floors
  • Design Review that cites the check behind every finding
  • An AI co-pilot that drafts changes — you approve each one
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How the calculations work →

Results are design estimates for preliminary sizing. Verify final designs against applicable codes and standards — engineering judgment and a licensed professional engineer’s review are required.