This cooling tower calculator computes heat rejection, range, approach, and the full water balance from operating conditions. Enter the hot and cold water temperatures, entering wet-bulb temperature, circulating flow, cycles of concentration, and drift loss; the tool returns cooling range, approach, heat rejected in tons and MBH, and the evaporation, drift, blowdown, and total make-up flows in GPM.
It also screens for common operating concerns — a tight approach below 5°F, a leaving water temperature above 95°F, and the Legionella growth band between 68°F and 113°F — so you can flag tower selection and water-treatment issues early.
| Range | HWT − CWT (°F) |
| Approach | CWT − WBT (°F) |
| Heat rejected | Tons = GPM × Range ÷ 24 · MBH = Tons × 12 |
| Evaporation | GPM × 0.0085 × (Range ÷ 10) |
| Blowdown | Evaporation ÷ (CoC − 1) |
| Make-up | Evaporation + Drift + Blowdown |
These follow standard cooling-tower and CTI practice. The factor 24 converts GPM and range to tons (one ton = 12,000 BTU/hr, and water heat transfer is GPM × ΔT × 500 BTU/hr, so 12,000 ÷ 500 = 24). Evaporation is approximated at ≈0.85% of circulating flow per 10°F of range, the common rule of thumb — actual evaporation varies with fill type and ambient conditions. Blowdown controls dissolved-solids buildup through the cycles of concentration.