The chiller sizing formula
A process chiller removes heat from a circulating fluid – usually water or a water-glycol mix – that cools equipment such as injection molds, lasers, CNC spindles, fermenters or MRI machines. The heat removed equals the flow rate multiplied by the temperature drop and the fluid's heat-carrying capacity. For water in US units that constant is 500 (8.33 lb per gallon × 60 minutes × specific heat 1.0).
BTU/h = GPM × 500 × ΔT (°F) · Tons = BTU/h ÷ 12,000 · kW = BTU/h ÷ 3,412
Example: 20 GPM of water warmed from 60 °F to 70 °F carries 20 × 500 × 10 = 100,000 BTU/h, or 8.3 tons. With a 20 % safety factor you'd choose a 10-ton chiller.
Corrections that matter
| Factor | Effect |
|---|
| Glycol | Lower specific heat – 30 % propylene glycol carries about 11 % less heat per GPM than water |
| Hot ambient air | Air-cooled chillers lose roughly 1 – 1.5 % capacity per °F above 95 °F |
| Low leaving temperature | Capacity drops about 1.5 – 2 % per °F below 50 °F |
| Future expansion | Add 10 – 25 % safety margin |
Typical applications
- Plastics injection molding: roughly 1 ton per 30 – 40 lb/h of material processed.
- Lasers and welders: chiller capacity at least equal to the equipment's waste heat in kW.
- Breweries: fermentation and crash cooling loads depend on batch size and schedule.
- Machine tools: spindle and coolant cooling, typically small 0.5 – 3 ton units.
Air-cooled or water-cooled?
Air-cooled chillers reject heat to surrounding air; they're simpler and cheaper to install but must be sized for the hottest day and can heat up an indoor plant. Water-cooled chillers reject heat to a cooling tower and are more efficient and compact, but need tower maintenance and water treatment. For large central plants, water-cooled systems usually win on operating cost.
Specifying a chiller
- Required capacity at your leaving temperature and maximum ambient.
- Flow rate and pressure available from the integrated pump.
- Reservoir size for thermal stability with intermittent loads.
- Temperature stability (±0.5 °F or tighter for lasers and medical equipment).
- Refrigerant type, electrical supply and outdoor rating.
Frequently asked questions
How do I calculate chiller tonnage?
Tons = GPM × 500 × ΔT (°F) ÷ 12,000 for water. Add a 10 – 25 % safety factor and corrections for glycol and ambient temperature.
How many kW is one ton of refrigeration?
One ton equals 12,000 BTU/h or about 3.517 kW of cooling.
Do I need glycol in my chiller?
Use glycol if the supply temperature is below about 45 °F or the chiller or piping is outdoors in freezing weather.
What size chiller for a 30 kW heat load?
30 kW is about 8.5 tons; with a 20 % margin choose a 10-ton chiller.
Air-cooled or water-cooled chiller?
Air-cooled is simpler for small and medium loads; water-cooled is more efficient for large central plants with cooling towers.
About ChillerSize
ChillerSize is an independent, free sizing calculator for process and industrial water chillers used in plastics, lasers, machining, breweries, food processing and medical equipment. Confirm final sizing with the chiller manufacturer. We are not affiliated with any chiller brand.
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The methodology combines widely published engineering rules of thumb, manufacturer data sheets and the electrical code practices that installers use every day. We review the assumptions regularly and update the calculator when typical product specifications change.
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Last updated: October 28, 2026
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