What size commercial AC do you need for a 3,000 sq ft Office? An office of this size carries a moderate internal heat load (standard office lighting and computers), so it typically needs about 9.2 tons of cooling — best installed as 2 × 5-Ton RTUs for redundancy — plus about 480 CFM of fresh air (ASHRAE 62.1). The calculator below is pre-set to this space.
Commercial Cooling Loads for a Office
Sizing an air conditioning system for a Office is drastically different from residential Manual J calculations. A Office introduces specific, high-intensity internal heat gains—from specialized equipment, concentrated lighting, changing occupancy densities, and strict ventilation codes requiring fresh outside air. You cannot use a generic square-footage rule of thumb. Use the commercial calculator below to account for these heavy sensible and latent heat loads to ensure your facility maintains a comfortable, safe, and code-compliant environment.
🏢 Commercial Cooling Tonnage, RTU Staging & CFM
Size commercial HVAC for offices, retail, restaurants, server rooms and warehouses. Get the required cooling tonnage, a recommended rooftop unit (RTU) staging combination, and the fresh-air ventilation CFM — factoring business type, occupancy, internal heat loads, ceilings and climate.
🏢1. Building Type
Each building type carries a different internal heat load — a restaurant kitchen or server room runs far hotter than an office or warehouse.
📐2. Floor Area & Ceiling
Range: 500 – 50,000 sq ft
👥3. Occupancy & Internal Loads
Auto-set from building type & area — adjust to your peak headcount.
🌍4. Climate & Unit Staging
Multiple staged RTUs give redundancy (if one fails, the building stays partly cooled) and better part-load efficiency — the commercial standard.
3,000 Sq Ft Office Cooling Load by Climate
The same 3,000 sq ft Office needs more cooling in a hotter climate. Recommended tonnage and RTU staging:
| Climate | Cooling Load | Recommended RTUs |
|---|---|---|
| Northern / Mild | 9.2 tons | 2 × 5-Ton RTUs |
| Humid South | 10.1 tons | 2 × 6-Ton RTUs |
| Sunbelt / Desert | 10.6 tons | 2 × 6-Ton RTUs |
Why a 3,000 Sq Ft Office Needs 9.2 Tons
Commercial cooling load comes from four sources: the building envelope (3,000 sq ft × a per-square-foot factor × ceiling height), occupancy (about 20 people here at 400 BTU/hr each), equipment & lighting, and sun/climate. For an office, the moderate internal load from standard office lighting and computers is the deciding factor — which is why it needs far more cooling than an office of the same size. Commercial installs almost always use staged rooftop units (2 × 5-Ton RTUs) so the building stays partly cooled if one unit fails. Fresh-air ventilation adds 480 CFM (ASHRAE 62.1), and total supply airflow is about 3,690 CFM.
Frequently Asked Questions
What size AC does a 3,000 sq ft Office need? About 9.2 tons of cooling in a moderate climate — roughly 325 sq ft per ton — typically installed as 2 × 5-Ton RTUs. Hotter climates push this higher.
How many rooftop units for a 3,000 sq ft Office? We recommend 2 × 5-Ton RTUs (10 tons installed). Multiple staged RTUs give redundancy and better part-load efficiency than one large unit.
How much fresh air (CFM) does a 3,000 sq ft Office need? About 480 CFM of outdoor air under ASHRAE 62.1, based on ~20 occupants plus floor area. Total supply airflow is around 3,690 CFM.
Background: how industrial refrigeration systems are built.
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Figures are reviewed by the Refcon HVAC engineering team using U.S. DOE, ENERGY STAR & ACCA Manual J data. Estimates only — confirm with a licensed pro.