How to use it

Review the methodology below to make sure it aligns with your project's requirements, then:

Choose US or metric units. Switching converts the values you have entered.
Give the condensate flow: either calculate it from the coil's entering and leaving dry-bulb and wet-bulb temperatures and its airflow, or enter it directly.
Choose the application (the kind of equipment the pump serves) and the voltage available.
Enter the head height: the vertical lift from the pump to the highest point of the discharge line.
The pumps that deliver at least the condensate flow at that head appear in the results, smallest first, with their flow at the head and their largest rated flow.

Use Copy link to these results to save or share the selection.

Methodology

Condensate generated

The condensate is the moisture the coil removes from the air:

Condensate (lb/h) = Airflow (cfm) × 60 ÷ v × (W_entering − W_leaving) ÷ 7000

where v is the specific volume of the entering air (ft³/lb) and W the humidity ratio in grains per pound, each from the dry-bulb and wet-bulb temperatures and the altitude, using the ASHRAE Handbook—Fundamentals psychrometric equations. One gallon of condensate weighs about 8.345 lb, so gph = lb/h × 0.11983. This is the same calculation as our condensate calculator.

Pump selection

A pump suits the job when it is made for the application and the voltage, and its flow at the head height is at least the condensate flow. Manufacturers rate condensate pumps at a few heads only, so between those heads the calculator takes the pump's flow at the next higher listed head, which is conservative. Above a pump's highest listed head it is not rated, and is not listed.

Condensate pumps run on a float switch: the pump starts when the reservoir fills and stops when it empties. A pump with more capacity than the condensate simply runs for shorter periods, so the calculator does not rule out larger pumps. It lists them smallest first, since the smallest pump that does the job is usually the quietest and least expensive.

Example

A coil cooling 1,200 cfm from 80 °F dry bulb, 67 °F wet bulb to 55 °F dry bulb, 54 °F wet bulb, at sea level, makes about 13.2 lb/h, or 1.6 gph, of condensate (the calculator's starting values). For an air conditioner at 115 V with a 10 ft lift, 12 Little Giant pumps qualify, starting with the VCMA-15 models at 25 gph at 10 ft. The VCL-24 models are rated only up to 9 ft, so they drop out at a 10 ft lift.

Notes

The pump data are Little Giant's catalog ratings. Confirm the selection, the reservoir size and any safety-switch wiring with the manufacturer's data.
Size the discharge line and allow for its friction: long or small-diameter tubing adds to the effective head.
Hi-temperature models are for plenum applications and condensing appliances with hot condensate; check the maximum liquid temperature for your equipment.