Selecting a pump when building a new system is crucial. Without the right size pump your system will not perform correctly. Here is an easy way to figure out what size pump you will need. Different types of systems have different methods for determining the size of the pump needed.

In determining the size of the pump need you will need to know two things. One is how much water is needed to be pumped each watering cycle. Two is how high the water has to be pumped. All pumps are rated for flow at a designated "head height", or how high the water needs to be pumped. A pump trated at 275 gph is usually will pump 275 gph to a heigth of 1 foot. That same pump may only pump 40 gallons of water to a heigth of four feet.

Ebb and Flow
First we will determine the size pump needed for an ebb and flow system. In this example the tray is 4 feet long x 2 feet wide and the desired depth of the nutrient is 4 inches. The water need to be pumped up 4 feet (48" head height).

To figure out how much water the ebb and flow tray holds:
4' long x 2' high = 48" long x 24" wide x 4" deep = 4608 cubic inches

Divide 4608 by 231 (231 is the number of cubic inches per gallon) = 19.9 gallons. This is what the tray will hold when filled to the desired depth with nutrient solution. This does not take into account the amount of nutrient solution displaced by the growing media, which may be as high as 50% or more.

Add 30% so that you have a leaching effect on excess nutrients in the media, and you come up with 25 gallons per cycle. Usually you want each ebb and flow cycle to last less than 30 minutes, 30 minutes or less filling, 15 minutes (or less, less is better) draining. So your pump must be capable of pumping around 50 gallons of water per hour at a head height of 48", if you figure that it has to pump around 25 gallons in 30 minutes. In this application a Maxijet 1000 or a Mag Drive 250 would work.

Drip/ trickle feed
Determining pump size for a trickle drip feed system is a little different. First you need to figure out how much water you want each plant to receive. A full size tomato plant could use as large as a 4 gph dripper, while smaller plants could use as low as 1/2 gph emitters. Since ( in my experience) you want each water cycle to be under 30 minutes, use an emmiter that is rated at twice the gallons per hour as you want the plant to recieve. If you want each plant to recieve 1 gallon of water per 1/2 hour water cycle, use 2 gph emitters.

Then multiply:
number of drip emitters you have x the rated output of the emitters per hour
This will tell you how much water needs to be pumped per hour.
Use a pump that will supply that much water at the head height designated

For example if you have 20 - 2 gph drippers you need 40 gallons of water pumped per hour or 20 gallons of water pumped every 1/2 hour to the desired head height.