How do you size commercial AC for an office? Offices carry a moderate internal heat load from standard office lighting and computers, so they need much more cooling than an equivalent office. A typical 5,000 sq ft Office needs about 15.4 tons (2 × 8.5-Ton RTUs). The calculator below is pre-set to a Office — enter your exact area.
Commercial HVAC Demands for a Office Building
Sizing an HVAC system for a Office Building involves complex variables that far exceed standard residential calculations. A Office Building experiences intense internal heat gains from specialized electronics, high-density lighting, and fluctuating occupancy levels throughout the day. Furthermore, commercial building codes mandate specific fresh air ventilation rates, which drastically increases the latent moisture load the AC must remove. Use our commercial calculator to properly size your rooftop units or CRAC systems to ensure your Office Building remains safe, comfortable, and code-compliant.
🏢 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.
Office AC Size by Floor Area
Typical commercial cooling load and RTU staging for an office in a moderate climate (standard ceilings):
| Floor Area | Cooling Load | Recommended RTUs |
|---|---|---|
| 1,000 sq ft | 3.1 tons | 1 × 4-Ton RTU |
| 2,000 sq ft | 6.1 tons | 1 × 7.5-Ton RTU |
| 3,000 sq ft | 9.2 tons | 2 × 5-Ton RTUs |
| 5,000 sq ft | 15.4 tons | 2 × 8.5-Ton RTUs |
What Drives Office Cooling Load
For an office, the biggest factor is the moderate internal heat from standard office lighting and computers, on top of the building envelope and occupancy. Occupancy density and glazing swing the number most. Commercial systems stage multiple rooftop units for redundancy and part-load efficiency. Confirm the final design with a licensed mechanical engineer.
Frequently Asked Questions
How do you size AC for an office? Start with the floor area and building type, then add occupancy, equipment and climate. Offices run a moderate internal load, so a 5,000 sq ft space needs about 15.4 tons (2 × 8.5-Ton RTUs).
How many tons of AC per square foot for an office? Roughly 1 ton per 325 sq ft for an office at standard conditions — heavier than an office. Use the calculator above for your exact size and climate.
Do Offices need multiple rooftop units? Yes, once the load passes about 7.5 tons — staged RTUs keep the building partly cooled if one fails and run more efficiently at partial load.
For larger plant, see industrial refrigeration system fundamentals.
Estimates vary by contractor. Compare free quotes from licensed local pros before you commit. Request a quote →
High-efficiency systems may qualify for utility rebates and federal or state incentives. Find current programs at ENERGY STAR & DSIRE.
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.