How commercial sizing differs from residential
Homes are sized with ACCA Manual J; commercial buildings use ACCA Manual N (light commercial) or ASHRAE methods. Commercial loads are driven less by the walls and roof and more by internal heat gain - people, lighting, computers, and kitchen or refrigeration equipment - plus the outdoor ventilation air required by ASHRAE 62.1. Equipment is usually one or more packaged rooftop units (RTUs), often with variable air volume (VAV) zoning and a building automation system so each area can be controlled on its own.
Square feet per ton by building type
The fastest ballpark divides floor area by a square-feet-per-ton figure that reflects how much heat the space generates. The denser and hotter the use, the fewer square feet each ton can cover.
| Building type | Sq ft per ton | What drives the load |
|---|---|---|
| Office | 300 - 400 | Workstations, lighting, plug loads |
| Retail store | 250 - 350 | Display lighting, foot traffic, door cycling |
| Restaurant / bar | 100 - 200 | Kitchen heat, occupancy, hood exhaust |
| Medical / dental | 250 - 350 | Equipment, ventilation, tight comfort control |
| School / classroom | 250 - 350 | High occupant density during class hours |
| Church / assembly / gym | 150 - 250 | Crowd-driven peaks, high ceilings |
| Warehouse / storage | 500 - 1,000 | Low occupancy, ventilation, ceiling height |
| Server / data room | 200 - 300 | Equipment heat running 24/7 |
Planning ranges only. Hot inland climates like Sacramento lean toward the denser end of each range.
The factors that move the number
Beyond square footage, the load rises with occupant density, internal heat gain from lighting and equipment, kitchen exhaust and makeup air, ceiling height and cubic volume, building orientation and glazing, and climate. It falls with better insulation and a tighter envelope, and a diversity factor trims the total because not every zone peaks at the same moment. Restaurants land lowest on square-feet-per-ton because kitchen heat, packed dining rooms, and hood exhaust stack up. Oversizing hurts too: a too-large commercial unit short-cycles, controls humidity poorly, and wastes energy.
Sacramento example. A 6,000 sq ft office at roughly 350 sq ft per ton needs about 17 tons - usually two rooftop units rather than one, so zones can be controlled separately. Most commercial permits require a stamped ACCA Manual N or ASHRAE load calculation, which we provide with a written equipment proposal.
Commercial Sizing Questions, Answered
How many tons of HVAC do I need per square foot of commercial space?
A common commercial rule of thumb is about one ton of cooling for every 300 to 600 square feet, but it varies sharply by building type. Offices run roughly 300 to 400 sq ft per ton, retail 250 to 350, and restaurants just 100 to 200 because of kitchen heat and high occupancy. Hot inland climates like Sacramento lean toward the denser end of each range. Use the calculator above for a starting point, then confirm with a Manual N load calculation.
How do you size a commercial HVAC system?
Commercial systems are sized with ACCA Manual N or ASHRAE methods, not the residential Manual J. The calculation weighs internal heat gain from people, lighting, and equipment, the outdoor ventilation air required by ASHRAE 62.1, the building envelope and climate, and a diversity factor for zones that do not all peak at once. A square-feet-per-ton rule of thumb gives a planning estimate; the stamped calculation gives the number you build to.
How many square feet will one ton cool in an office, restaurant, or warehouse?
Roughly: an office about 300 to 400 sq ft per ton, a restaurant only 100 to 200 sq ft per ton because of kitchen and occupancy heat, and a warehouse 500 to 1,000 sq ft per ton thanks to low occupancy. The denser the heat load, the fewer square feet each ton can cover.
Why do restaurants need more cooling than offices?
Restaurants combine three heavy loads: cooking equipment that throws off large amounts of heat, packed dining rooms full of people, and kitchen hood exhaust that pulls conditioned air out of the building. The makeup air replacing that exhaust also has to be cooled. Together these push restaurants to the densest sizing, often 100 to 150 sq ft per ton.
What is a rooftop unit (RTU)?
A rooftop unit, or RTU, is a packaged commercial HVAC system that houses the compressor, coils, and blower in one cabinet installed on the roof. Most light-commercial buildings use one or more RTUs, commonly from 2 to 30 tons, often paired with variable air volume (VAV) zoning so different areas can be controlled separately.
Do I need an engineer or permit to size a commercial HVAC system?
For most commercial installations and replacements, yes. Jurisdictions typically require a stamped mechanical design and a permit, especially when new equipment, ductwork, or makeup air is involved. Use this calculator to plan and budget, then have a licensed contractor or mechanical engineer produce the Manual N or ASHRAE design for the permit.
Sizing a Commercial System?
We run a full commercial load calculation - ACCA Manual N or ASHRAE - and spec rooftop or split equipment to match, with a written proposal and no obligation.