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Condenser Sizing Calculator

Work out condenser sizing instantly with clear inputs, formula shown and shareable results.

About Condenser Sizing Calculator

A condenser must reject the evaporator load plus the work the compressor added, so the duty is always larger than the cooling capacity, typically by 15 to 25 percent. Airflow follows from the sensible relation 1.08 x CFM x ΔT and coil area from Q = U x A x ΔT.

Formulas

Heat rejection

Q reject = evaporator load + compressor kW x 3412

Air side

CFM = Q reject / (1.08 x air ΔT); A = Q reject / (U x ΔT)

Worked example

With the default values below, Condenser Sizing Calculator returns Heat rejection duty of 46,919. Change any input above and every figure here is recalculated in your browser.

Inputs used

Evaporator loadminimum 1 BTU/h
36,000 BTU/h
Compressor power inputminimum 0.1 kW
3.2 kW
Air temperature rise across coilminimum 1 °F
15 °F
Coil heat transfer coefficientminimum 1 BTU/h·ft²·°F
30 BTU/h·ft²·°F

Results

Heat rejection duty
46,919 BTU/h
Condenser airflow
2,896 CFM
Coil surface area required
104.3 ft²
Rejection to evaporator load ratio
1.303

Step by step

  1. 1Values used
  2. 2Heat rejection
  3. 3Air side
  4. 4Heat rejection duty= 46,919 BTU/h
  5. 5Condenser airflow= 2,896 CFM
  6. 6Coil surface area required= 104.3 ft²
  7. 7Rejection to evaporator load ratio= 1.303

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 or compounding frequency into account.
  • Figures are rounded for display to 3 decimal places, 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 Condenser Sizing figure worked out?

Q reject = evaporator load + compressor kW x 3412. A condenser must reject the evaporator load plus the work the compressor added, so the duty is always larger than the cooling capacity, typically by 15 to 25 percent.

What happens if the condenser is undersized?

Condensing temperature and pressure climb, which cuts capacity, raises compressor power and shortens compressor life.

What values do I need to enter?

This calculator takes 4 inputs: Evaporator load, Compressor power input, Air temperature rise across coil, Coil heat transfer coefficient. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.

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Condenser Sizing Calculator – Calculate Heat rejection duty