Design Sanity Checker

Paste in your design numbers — CFM, tons, SF, GPM, MBH — and get instant high/normal/low flags against industry rule-of-thumb ranges.

📋 Your Design Numbers

🔍 Sanity Check Results

Run this for your whole project — free →
Start a free 14-day trial. No credit card.

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

Cooling densityft²/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

Each ratio is compared to a typical range for the chosen building type. A value below 80% of the low end fails; a value above 120% of the high end, or otherwise outside the range, warns; in-range passes. The benchmark ranges and the 350–500 CFM/ton coil rule reflect common HVAC rule-of-thumb practice and ASHRAE guidance — they are screening values, not code minimums, and never replace a room-by-room load calculation.

❓ 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. Each metric gets a pass, warn, or fail flag so you can spot an outlier before it reaches a drawing.
How are the pass, warn, and fail flags decided?
A value inside the typical range for the selected building type passes. A value just outside the range, or more than 20 percent above the high end, is flagged as a warning. A value below 80 percent of the low end is flagged as a fail. The bands are intentionally forgiving because rule-of-thumb ranges are 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 offices the tool uses about 200 to 350 square feet per ton. Denser loads like restaurants run lower (roughly 80 to 180), while warehouses run much higher (500 to 1,000). 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
Free 14-Day Trial  ·  No Credit Card

Do the full calculation in AIM Works

This calculator handles one step. AIM Works runs the complete MEP design workflow — thermal load calculations, duct & pipe networks, equipment selection, code compliance, and an AI design assistant — in one tool.

  • ✓  ASHRAE 62.1 ventilation + CLTD/CLF/RTS load methods
  • ✓  Darcy-Weisbach pipe & duct network solvers
  • ✓  ASHRAE 90.1 / IMC / NFPA advisory compliance checks
  • ✓  20 free AI design messages included in trial
Try It Free for 14 Days →
No credit card  ·  Cancel anytime
See plans & pricing →

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.