AC for Gym: How Many Ton? Sizing, Fresh Air and Star Ratings

For a gym, size the AC from your peak-hour heat load, not from square feet: people exercising, treadmills and lights, sun on walls and glass, and the fresh air you bring in. One person training hard gives off about 1,800 Btu/h according to ASHRAE's occupant heat-gain values, which is 0.15 ton of refrigeration (TR), so 30 people need about 4.5 TR for themselves alone. In the worked example below, a busy 2,000 sq ft gym comes to roughly 11 to 12 TR, about one ton per 180 sq ft.

The usual mistake is a contractor sizing the room like a shop or office, then the gym is fine at 11 am and miserable at 7 pm. Here's how to check the number yourself before you buy.

Why doesn't a square-foot rule work for gyms?

Area-based rules assume a fairly steady load: a few people sitting, some lights, the sun. A gym's load swings hard with the crowd, and exercising people put out several times the heat of someone at a desk.

These are the per-person values Autodesk reproduces from the ASHRAE Handbook, Fundamentals. Two things stand out. An exercising member gives off about 4.5 times the heat of someone seated doing very light work (1,800 ÷ 400). And about 60% of it is latent heat, meaning moisture from sweat and breath (1,090 ÷ 1,800). That's why an undersized gym AC leaves the room sticky even when the remote says 24°C.

How do you convert heat into tons?

The Bureau of Energy Efficiency defines one ton of refrigeration as 12,000 Btu/h, or 3.516 kW of cooling. Two conversions do all the work:

• Btu/h to TR: divide by 12,000.
• Electrical load to heat: almost every watt a treadmill, light or TV draws ends up as heat in the room. 1 kW = 12,000 ÷ 3.516 = about 3,413 Btu/h.

A worked heat-load example

Hypothetical: a 2,000 sq ft gym, 10 ft ceiling, first floor, some west-facing glass. At the 7 pm peak there are 30 people on the floor.

Round up to about 12 TR, for example six 2-ton units spread across the floor, or a ducted system of similar capacity. That's 2,000 ÷ 11.3 = about 177 sq ft per ton. If a quote for the same room is far below this, ask the contractor how they counted people and fresh air.

The two "contractor's figure" lines need a proper calculation for your building, because a top-floor gym with a bare roof or a wall of west glass can carry much more. Ask the contractor for the written heat-load calculation behind the quote.

Where to place the units

Put the most cooling where the heat is: the cardio row and the functional area, not reception. Several smaller units also mean one breakdown doesn't shut the gym. The gym layout guide has notes on aiming AC throw across the busiest zones.

How much fresh air does a gym need?

A split AC moves the room's own air through a cold coil. It doesn't bring in outdoor air, so on a busy evening the room fills with moisture, odour and CO2 from breathing.

India's National Building Code 2016 has a section on air conditioning, heating and mechanical ventilation, but it's a priced BIS publication we couldn't check for a gym-specific rate. Ask your HVAC designer which rate they're using. An openly published reference is the US mechanical code's ventilation table, shown here as adopted by Washington State:

For the example gym: 30 people × 20 cfm + 2,000 sq ft × 0.06 cfm = 600 + 120 = 720 cfm of outdoor air. The room holds 2,000 × 10 = 20,000 cu ft, so that's 720 × 60 ÷ 20,000 = about 2.2 air changes of outdoor air an hour.

That outdoor air arrives hot and, in coastal or monsoon months, humid, so it adds to the cooling load (the 2 TR line above). This is why fresh air and AC tonnage have to be planned together.

Ways to bring fresh air in

• Inline fresh-air fan with a filter, ducted to the floor. Cheapest; adds load to the splits.
• Treated fresh-air unit that pre-cools and dries outdoor air before it enters. Better in humid cities.
• Energy recovery unit that swaps heat and moisture between outgoing and incoming air. Higher cost, lower running load.
• Exhaust from changing rooms and toilets that runs whenever the gym is open, so smells don't drift to the floor.

Ducted or split: which suits a gym?

Many smaller gyms do well with several splits plus a dedicated fresh-air fan. Larger gyms with ceiling space often find ducted systems easier to keep even across the floor.

What do BEE star labels tell you?

BEE's star label for room ACs covers both fixed-speed and inverter units up to 10,465 W, or 2.97 TR. The rating uses ISEER, a seasonal figure based on hours spent at different outdoor temperatures (the bin hours in ISO 16358), so it reflects how an AC runs across a whole season, not just at full blast. Since 1 January 2020, star-labelled units must ship with a 24°C default.

Bigger non-ducted splits, above 10.5 kW and up to 18 kW, have their own light commercial AC schedule. Ducted systems aren't covered by either, so ask the supplier for rated efficiency and test conditions in writing.

Practical points:

• Compare the ISEER number and the label year, not just the stars. BEE tightens the bands over time, so the same efficiency can earn fewer stars under a newer table.
• Inverter units suit gyms because the load swings from near-empty afternoons to packed evenings; a seasonal rating like ISEER captures part-load running.
• Running costs are where the label pays back. The electricity bill guide covers 24°C settings, filters and the maths.

Using a CO2 monitor as a ventilation check

A desk-top CO2 monitor is a cheap way to see whether fresh air is keeping up with the evening crowd. Two cautions from ASHRAE's position on indoor CO2: CO2 doesn't give an overall indication of air quality, and sensor accuracy, location and calibration are critical for drawing meaningful conclusions. The indoor-outdoor difference can be used to judge ventilation, but only if several assumptions hold.

Exercise also matters. CO2 output depends on body size and physical activity, as Persily's work on occupant generation rates explains, so people training hard produce more CO2 than people sitting, and readings run higher for the same airflow per person. Use the monitor for trends:

1. Note an outdoor reading first.
2. Place the monitor at head height, away from doors, AC vents and the front desk where staff breathe on it.
3. Log it at opening, at the peak hour and an hour after.
4. If the level climbs all evening and barely falls after the crowd leaves, fresh air is short. Fix the supply, then check again.

Quick checklist

• Count your peak-hour crowd, not average attendance (the gym capacity calculator estimates it from floor area)
• Heat load done by the contractor: people (1,800 Btu/h each), equipment, envelope, fresh air
• Tonnage rounded up and split across several units, aimed at cardio and functional zones
• Outdoor air planned: about 20 cfm per person plus 0.06 cfm per sq ft as a reference
• Exhaust in changing rooms and toilets
• BEE label checked for ISEER and label period; inverter units preferred
• Ducted system efficiency and test conditions in writing
• CO2 monitor logged at the evening peak

Useful links

• BEE: energy performance assessment of HVAC systems (ton of refrigeration)
• ASHRAE occupant heat gains, as reproduced by Autodesk
• Ventilation rate table, Washington State mechanical code
• PIB: BEE standards for room air conditioners
• BEE schedule for light commercial ACs
• ASHRAE position document on indoor CO2 (summary by its authors)