Estimate the cooling tonnage your office, retail, restaurant, warehouse, or light-industrial space actually needs — accounting for square footage, ceiling height, occupant density, equipment heat load, and sun exposure on Alabama-summer peak days.
Enter building square footage to calculate.
The short version: commercial buildings get sized by use-type heuristics, then adjusted for ceiling volume, occupant density, internal equipment heat, and solar gain. This calculator runs that math in your browser using the per-ton baselines published in ACCA Manual N and ASHRAE 90.1 commercial-load methodology.
The Air Conditioning Contractors of America (ACCA) publishes Manual N — Commercial Load Calculation as the industry standard for sizing commercial HVAC equipment. It is the commercial counterpart to Manual J (residential). Manual N starts from envelope load — wall, roof, glass, and infiltration heat gain calculated against the local design temperature. For Birmingham, ASHRAE design day is approximately 96°F dry-bulb, 77°F wet-bulb at the 1% cooling load condition. Manual N then layers internal gains: people, lighting, plug load, cooking equipment, motors.
The square-foot-per-ton heuristics this calculator uses are the field-grade simplification of that methodology. For commercial buyers running sanity checks before calling a contractor, or building owners budgeting capital for an HVAC replacement, the heuristic approach gets you within 10-15% of a permit-grade Manual N number. The places it falls short are buildings with unusual envelope characteristics — heavily glazed atrium designs, extremely tall ceilings, deep tenant-space build-outs with unusual internal latent gains. For those, run a real Manual N.
The American Society of Heating, Refrigerating and Air-Conditioning Engineers — ASHRAE Standard 90.1 — sets the energy-efficiency framework that commercial equipment is sized against, including the economizer requirements that influence cooling-load math for RTUs above specified size thresholds. The Air-Conditioning, Heating, and Refrigeration Institute (AHRI) certifies the BTU/hour ratings on commercial equipment.
Why use type matters so much: a 4,000 sq ft restaurant kitchen carries 16 tons of cooling load, while a 4,000 sq ft office carries 8 tons. The cooking-line equipment, dishwasher exhaust, hood-vented heat, and make-up air handling more than double the load. Restaurants in Birmingham routinely fail HVAC sizing because someone scaled up a residential heuristic instead of running the commercial number.
Why sun exposure matters: a west-facing storefront on Birmingham's Highway 280 corridor takes direct afternoon sun load through plate glass on the worst possible day — 4 PM in July when ambient temperature is also peaking. That building runs 10-15% over the calculated baseline. Conversely, a north-facing tenant suite with shade from neighboring buildings can run 10% under baseline. ACCA Manual N handles this in the solar-gain coefficient; this calculator handles it as a multiplier on the total.
If you are sizing equipment for a permit-grade application — new construction, full HVAC replacement going through the City of Birmingham permitting office, or a tenant build-out subject to mechanical inspection — get a licensed commercial mechanical engineer to run a full Manual N calculation. The cost is modest compared to the cost of oversizing or undersizing the equipment. Call (205) 206-6606 and we will route you to a coordinator who can walk the building or refer the engineering scope.
Submit a dispatch request or call the line for a Birmingham commercial site walk. We do not quote on heuristics — we walk the building.
Call (205) 206-6606 Request dispatchCommercial HVAC only. Submit the form and a dispatch coordinator follows up by email. For active outages, call (205) 206-6606.
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