Stop using 400 ft²/ton (which equals ~85 W/m²). That ignores windows, people, and latitude.
Let’s look at how to use the cooling load check figures to validate your model in under 10 minutes.
Open your ASHRAE Handbook—Fundamentals. In the current edition (2021/2025), Chapter 18 (Nonresidential Cooling and Heating Load) contains the gold mine: Table 9 & 10 , typically titled “Cooling Load Check Figures for Typical Commercial Buildings.” cooling load check figures ashrae pdf
“ASHRAE Cooling Load Check Sheet (PDF)” – A one-page checklist comparing W/m² for 12 building types. (Note: Create this as a lead magnet or internal tool.) Author Note: Always refer to the current ASHRAE Handbook—Fundamentals for official tables. Values cited here are for educational illustration of the methodology.
Let’s say you modeled a 2,000 m² (21,500 ft²) mid-rise office building (perimeter zones). Your software says total cooling load = 280 kW . Stop using 400 ft²/ton (which equals ~85 W/m²)
Find your building type. Calculate your W/m². Compare. Adjust. Only then do you have an engineering judgement you can defend.
We’ve all been there. You’ve spent three hours inputting walls, windows, roofs, and internal loads into your HAP, Trace, or IESVE model. The software spits out a number: 124.7 kW (35.6 tons) . Open your ASHRAE Handbook—Fundamentals
These tables provide (or Btu/h·ft²) ranges for total cooling loads based on building type and glazing percentage.
But does that feel right?
The 400 sq ft/ton Rule is Dead: How to Use ASHRAE Fundamentals to Sanity Check Your Cooling Loads
Blindly trusting the output is dangerous. Before you size a chiller or select an AHU, you need a rapid, engineering-based sanity check. While many engineers still whisper the old rule of thumb (400 sq. ft. per ton), ASHRAE Handbook—Fundamentals provides a much more accurate, albeit often overlooked, method for spot-checking results.