Formula & worked example
Range=Thot−Tcold; Approach=Tcold−Twb; ε=Range/(Thot−Twb); Q=ṁcpRange.
35°C hot water cooled to 29°C at 25°C wet bulb has 6 K range, 4 K approach and 60% effectiveness.
Heating & HVAC engineering calculator · Updated Sep 17, 2026
Cooling Tower Range & Approach Calculator — Effectiveness and Heat Rejection
Calculate cooling-tower range, approach, effectiveness and water-side heat rejection from hot/cold water and wet-bulb temperatures plus flow.
Inputs
Live result
Range 6 K
Approach 4 K
Tower effectiveness 60%
Water mass flow 27.694444 kg/s
Heat rejection 695.57367 kW (2,373,395.9 BTU/h)
Assumptions & limits
- Wet-bulb temperature must represent entering air conditions.
- Evaporation, drift, blowdown and fan power are outside this water-side energy balance.
Frequently asked questions
What does this Cooling Tower Range & Approach Calculator calculate?
Calculate cooling-tower range, approach, effectiveness and water-side heat rejection from hot/cold water and wet-bulb temperatures plus flow.
What units are supported?
Inputs state their unit basis and results include practical SI and US customary equivalents where useful, so the calculation can be checked against field data and equipment schedules.
Can I use this for final equipment selection?
Use it for transparent first-pass sizing and engineering cross-checks. Final selections should use measured conditions, manufacturer performance data and applicable codes or design standards.