Condensate Drain Sizing Calculator

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

About Condensate Drain Sizing Calculator

A cooling coil condenses roughly 1.5 to 3 pints of water per ton per hour depending on how humid the entering air is. Eight pints make a gallon, so daily volume follows from run hours. Drain diameter is set by code band rather than flow: three-quarter inch up to 20 tons, one inch beyond that.

Formula

Condensate volume

gal/day = tons x pints per ton-hour x run hours / 8

Worked example

With the default values below, Condensate Drain Sizing Calculator returns Condensate produced of 15.00. Change any input above and every figure here is recalculated in your browser.

Inputs used

Cooling capacityminimum 0.5 tons: 5 tons
Condensate rateminimum 0.2 pints/ton·h: 2 pints/ton·h
Run hours per dayminimum 1 h: 12 h

Results

Condensate produced: 15.00 gal/day
Condensate in litres: 56.8 L/day
Peak condensate rate: 10.00 pints/h
Minimum drain size: 0.75 in

Step by step

1Values used
2Condensate volume
3Condensate produced= 15.00 gal/day
4Condensate in litres= 56.8 L/day
5Peak condensate rate= 10.00 pints/h
6Minimum drain size= 0.75 in

Assumptions and limits

The result is derived only from the 3 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 2 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 Condensate Drain Sizing figure worked out?

gal/day = tons x pints per ton-hour x run hours / 8. A cooling coil condenses roughly 1.5 to 3 pints of water per ton per hour depending on how humid the entering air is.

Why must the drain have a trap?

Without a trap the drain pan connects the negative-pressure air stream to the drainage system, so the unit pulls sewer gas in and holds condensate in the pan instead of letting it flow.

What values do I need to enter?

This calculator takes 3 inputs: Cooling capacity, Condensate rate, Run hours per day. The pre-filled defaults are a realistic worked example — replace them with your own site or project figures.