HVAC Methodology & Editorial Standards

Last updated: October 6, 2026

How the calculator works

The room-load function on the calculator is a planning estimate, not a measured result and not a full ACCA Manual J. It starts at 25 BTU/hr per square foot. It multiplies by ceiling height ÷ 8, by a sun factor, and by an insulation factor, then adds 600 BTU/hr for each window. Sun factors are shaded ×0.90, average ×1.00, and very sunny ×1.15. Insulation factors are good ×0.85, average ×1.00, and poor ×1.25. The total is multiplied by 1.10 (a 10% margin) and rounded up to the nearest 500 BTU.

Mini-split heads on this site are 9,000, 12,000, 15,000, 18,000, 24,000, 30,000, and 36,000 BTU/hr. The mini-split tab picks the smallest head at or above that room load.

Duct airflow uses CFM = BTU/hr ÷ (ΔT × 1.08). The duct tab takes the equipment rating in BTU/hr. Electric baseboard watts are BTU/hr ÷ 3.41. The U.S. Department of Energy's Guide to Home Heating and Cooling equates one ton of cooling with 12,000 Btu. That ton figure is a unit conversion, not this calculator's room-load baseline.

Where the numbers come from

Factor tables on the calculator page state the 25 BTU/hr baseline, the sun and insulation multipliers, the window adder, and the 10% margin. Guide pages that quote a government chart link that chart in the sentence and again under Sources.

The mini-split BTU and SEER2 chart copies cooling capacity, SEER2, EER2, and HSPF2 exactly as published. Every row links its ENERGY STAR record and the single-zone source used to keep that family. The access date on that page is October 6, 2026. A blank field would say "not listed". Nothing on that chart is estimated. The same rows are in the CSV.

How pages are written

Page text is drafted with AI agents (Cursor and local models) from those sources.

Built and owned by Jeremy Panasuk, New Auburn, WI.

Affiliate policy

As an Amazon Associate I earn from qualifying purchases. The Amazon links below are affiliate links; they don't change the math.

Amazon links use the Associates tag generatorsi0d-20. The disclosure sits before the first affiliate link. Those links do not change calculator output. There are no paid placements.

Corrections

Spot an error? Email jpanasuk@gmail.com with the page URL.

Safety scope

Not a substitute for a licensed contractor/electrician or the equipment manual. The about page says the same limit in its own words: this is not a Manual J, and the owner is not a licensed HVAC contractor.