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Cooling Tower Capacity Calculator

Work out cooling tower capacity instantly with clear inputs, formula shown and shareable results.

About Cooling Tower Capacity Calculator

Tower duty is the water-side heat load, GPM x range x 500. Tower tons are quoted as 15,000 BTU/h rather than 12,000 because a tower also rejects compressor heat. Range is how far the water is cooled; approach is how close the cold water gets to the wet bulb, and it is the approach that governs tower size and cost.

Formulas

Heat rejected

BTU/h = GPM x range x 500, range = hot - cold water temperature

Tower tons

Tower tons = BTU/h / 15000; approach = cold water - wet bulb

Worked example

With the default values below, Cooling Tower Capacity Calculator returns Heat rejection capacity of 300.0. Change any input above and every figure here is recalculated in your browser.

Inputs used

Circulating water flowminimum 1 GPM
900 GPM
Hot water temperature inminimum 1 °F
95 °F
Cold water temperature outminimum 1 °F
85 °F
Design wet bulbminimum 1 °F
78 °F

Results

Heat rejection capacity
300.0 tons
Heat rejected
4,500,000 BTU/h
Cooling range
10.0 °F
Approach to wet bulb
7.0 °F

Step by step

  1. 1Values used
  2. 2Heat rejected
  3. 3Tower tons
  4. 4Heat rejection capacity= 300.0 tons
  5. 5Heat rejected= 4,500,000 BTU/h
  6. 6Cooling range= 10.0 °F
  7. 7Approach to wet bulb= 7.0 °F

Assumptions and limits

  • The result is derived only from the 4 inputs listed above. Anything not among them is not part of the calculation.
  • In particular, this calculator does not take inflation, tax, fees or charges or compounding frequency into account.
  • Figures are rounded for display to 1 decimal place, so totals built from several rounded parts can differ slightly from the unrounded arithmetic.

How these calculators are built and tested is described on the Methodology page. If a figure looks wrong, please report it.

Frequently Asked Questions

How is the Cooling Tower Capacity figure worked out?

BTU/h = GPM x range x 500, range = hot - cold water temperature. Tower duty is the water-side heat load, GPM x range x 500.

Why can a tower never beat the wet bulb?

Evaporative cooling drives water toward the wet bulb temperature asymptotically. A design approach below about 5 °F needs a disproportionately large tower.

What values do I need to enter?

This calculator takes 4 inputs: Circulating water flow, Hot water temperature in, Cold water temperature out, Design wet bulb. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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