Commercial · Load estimating
Commercial HVAC load calculator
Commercial cooling is driven by what happens inside the building, not by its volume. An open-plan office runs 300–400 sq ft per ton, a restaurant dining room 150–250, a conditioned warehouse up to 1,500. Use these figures to budget and to sanity-check a quote — then have a Manual N or ASHRAE calculation done for the real design.
Cooling load by building type
| Building type | Sq ft per ton | BTU/h per sq ft | Driver |
|---|---|---|---|
| Office, open plan | 300–400 | 30–40 | Moderate occupancy, high plug load |
| Office, private | 350–450 | 27–34 | Lower density |
| Retail store | 250–350 | 34–48 | Lighting and door traffic |
| Restaurant, dining | 150–250 | 48–80 | High occupancy, makeup air |
| Restaurant, kitchen | 100–150 | 80–120 | Cooking equipment dominates |
| Classroom | 200–300 | 40–60 | Dense occupancy in bursts |
| Medical / dental | 250–350 | 34–48 | Equipment plus ventilation |
| Warehouse, conditioned | 800–1500 | 8–15 | Envelope-driven, low internal gain |
| Gym / studio | 100–200 | 60–120 | Very high metabolic load |
Ranges assume a reasonably modern envelope in a temperate climate. Hot climates, single glazing and west-facing glass all push toward the low end of the sq-ft-per-ton column.
Server rooms are sized differently
IT heat load BTU/h = IT power (kW) × 3,412
tons = IT power (kW) × 0.284
10 kW of racks → 34,120 BTU/h → 2.8 tons, before UPS losses and envelopeNearly all electrical power drawn by IT equipment leaves as heat, so the load follows the meter rather than the floor plan. Add UPS and transformer losses, lighting and any envelope gain, then size for redundancy — that is usually what decides the equipment.
What a full commercial calculation adds
- Outdoor air. ASHRAE 62.1 sets ventilation by occupancy and floor area; conditioning that air is often the largest single load in a dense space.
- Occupancy schedules. Zones peak at different hours, so the plant is sized on a block load that is smaller than the sum of zone peaks.
- Internal gains. Lighting, plug loads, kitchen equipment and process heat, each with its own diversity factor.
- Latent load. Occupancy and outdoor air drive moisture that a sensible-only estimate ignores entirely.
- Zoning and control. How the load is split decides equipment selection as much as its total size.
Our room-by-room load calculator covers none of that — it is a residential-scale estimate. For a single small commercial space it will get you in the right range; for anything you quote from, it will not.
FAQ
- How do you calculate a commercial HVAC load?
- A proper commercial calculation follows ACCA Manual N or ASHRAE procedures: envelope gains hour by hour, occupancy density and schedule, lighting and plug loads, process equipment, and outdoor air per ASHRAE 62.1. The result is a peak load per zone plus a block load for the plant — the two differ, because zones do not peak at the same hour. Rules of thumb per square foot are for budgeting and sanity checks only.
- How many square feet per ton for a commercial building?
- It depends entirely on occupancy. A conditioned warehouse can run 800–1,500 sq ft per ton, an open-plan office 300–400, a restaurant dining room 150–250, and a commercial kitchen 100–150. Quoting a single number across building types is the most common way these estimates go wrong.
- How do I size cooling for a server room?
- By the IT load, not the floor area. Electrical power drawn by the equipment converts almost entirely to heat: 1 kW of IT load is 3,412 BTU/h, so a 10 kW rack needs about 34,000 BTU/h — nearly 3 tons — before adding UPS losses, lighting and envelope gains. Redundancy requirements usually drive the final selection more than the load itself.
- What about clean rooms?
- Clean rooms are sized by air change rate and filtration, not by cooling load alone. ISO class sets the required air changes — anywhere from about 20 per hour at ISO 8 to several hundred at ISO 5 — and the fan energy needed to move that air often becomes a large part of the cooling load itself. That is specialist design work.
- Can I use the room calculator on this site for a commercial job?
- For a first sanity check on a single small space, yes. For anything you will quote or build from, no: it has no model for outdoor air, occupancy schedules or process equipment, and commercial permits generally require a documented Manual N or ASHRAE-based calculation.