What HP pump for 12,000 s.f. lawn sprinkler system

[HoneyDo]

Hi. A totally do-it-yourselfer here. Planning a sprinkler system install. Running from a well. Need to know if a 1 1/2 HP pump is enough or if 2HP is overkill. We have no idea how deep the well is. The house used to run off well-water. Currently there's a 1 1/4" line from 2" well/head to 1 HP Flotec pump. We're running a new 2" intake from the well. There's never been a sprinkler system here. Husband is very skilled in his profession (Electrical Contractor) and has done/can do most everything he's attempted. We have a water-guy charging $100 to draw up the plan from the scale-model we gave of the house/lawn. He said "must know GPM and it must be a minimum of 30." Right now we are getting 21 GPM. Need to water approx. 12,000 s.f. Will a 1 1/2 HP pump (new Wayne WLS150) be enough and give us the 30 GPM that the guy charging us $100 says we need? Will 2HP be too much? Please advise.

[speedbump]

First of all, you don't buy pumps by horsepower. A two inch well may or may not do 30 gpm. A lot depends on the water level in that well. It has to be less than 25 feet or you can forget 30 gpm. You said your getting 21 gpm. What kind of Flotec pump do you have? A jet or a centrifugal? How are you doing this flow test? Are you testing the flow right out of the pump with no smaller than 1" pipe? Into a 5 gallon bucket maybe?

When you design a sprinkler system, you design it to the well, not the well to it. The system can be changed, the well can't. So before you spend the $100.00 on the drawing, do your pump test first. If that Flotec is a jet pump, 21 gpm may be all it can do. With a different pump, you may easily get the 30 gpm needed.