Water Chiller Sizing Calculator
Find the BTU/hr and HP rating your reservoir needs from volume and temperature, with optional light and room heat.
Include all water in the system: reservoir, buckets, and plumbing.
Measure at its warmest, during lights on with no chiller.
65 to 68 °F suits most hydro crops.
Leave 0 if the reservoir sits in a separate cooled room.
Minimum chiller size0 BTU/hr with 20% buffer
- Temperature differential
- 0.0 °F
- Base load (water pull-down)
- 0 BTU/hr
- Light heat to water
- 0 BTU/hr
- Ambient adjustment
- 0%
- Total before buffer
- 0 BTU/hr (0.00 tons)
- Size up one tier
A larger chiller runs fewer hours and lasts longer. Sizing up one tier is the usual advice.
Chiller sizes and formula
| Chiller | Capacity | Reservoir range (DWC) | Reservoir range (NFT / drip) |
|---|---|---|---|
| 1/10 HP | about 800 BTU/hr | up to 26 gal | up to 35 gal |
| 1/4 HP | about 2,500 BTU/hr | 26 to 65 gal | 35 to 90 gal |
| 1/2 HP | about 5,500 BTU/hr | 65 to 145 gal | 90 to 190 gal |
| 1 HP | about 10,000 BTU/hr | 145 to 265 gal | 190 to 350 gal |
| 1.5 HP | about 15,000 BTU/hr | 265 to 400 gal | 350 to 525 gal |
| 2 HP | about 20,000 BTU/hr | 400+ gal | 525+ gal |
BTU/hr = gallons × 8.34 × temperature differential × system factor. Advanced adds 10% of light wattage as heat reaching the water (watts × 3.412 × 0.10) and 2% per °F that ambient exceeds 75 °F. Then a 20% safety buffer. Tons = BTU/hr ÷ 12,000.