THE NUMORIX GUIDE
How to use the BTU Calculator
Last reviewed September 14, 2026
What this calculator does
The engine scales heating demand as square feet x the entered climate factor x ceiling height / 8.
Formula and method
The engine scales heating demand as square feet x the entered climate factor x ceiling height / 8. Cooling demand is square feet x 20 x ceiling height / 8, regardless of the climate input. Air-conditioning tons are cooling BTU/hr divided by 12,000, and the displayed heating and cooling values are rounded to whole BTU/hr.
Variables and inputs
Enter floor area in square feet, the positive climate factor shown as 20-50 in the UI, and ceiling height in feet. The height factor is 1.00 at an 8-foot ceiling. The engine accepts any positive climate value even though the label suggests a 20-50 range.
Worked example
For 1,500 sq ft, climate factor 30, and an 8 ft ceiling, the height factor is 8 / 8 = 1. Heating is 1,500 x 30 x 1 = 45,000 BTU/hr. Cooling is 1,500 x 20 x 1 = 30,000 BTU/hr, or 30,000 / 12,000 = 2.50 tons.
How to interpret the result
These are quick heat-load estimates for the entered floor area and ceiling height. The heating and cooling results are separate rule-of-thumb outputs; the heating climate factor does not change the cooling formula.
Common mistakes to avoid
Use the conditioned floor area rather than the lot size, enter ceiling height in feet, and keep climate factor as a number such as 30 rather than 0.30. Do not interpret cooling tons as an exact equipment recommendation.
Assumptions and limitations
The engine does not account for insulation, windows, solar exposure, air leakage, occupancy, duct losses, equipment efficiency, local design temperatures, or room-by-room loads. It also applies a fixed cooling factor of 20 and does not add a safety margin. A contractor should perform a proper load calculation before sizing equipment.