A 0.5HP water pump can be enough for a home, depending on how deep the well is and the required flow rate. Most likely a 0.5HP water pump would work for a home some combination of the following; a smaller residence, with just one or two people living there, and the home is using a relatively shallow well.
A pump is sized based on a calculation of “total dynamic head”. Total dynamic head is a measure of how strong a pump needs to be in order to lift the water up to the top of the well, and in residential cases, push into a pressure tank. The deeper the well, the more powerful the pump is needed.
Total dynamic head = total well depth + feet of head from pressure tank + any vertical lift from well to pressure tank + frictional loss from length of pipe
If you know the static water level in your well, you can substitute that number for total well depth (and most likely fit into a smaller HP pump). But most people only know the total depth.
The PSI rating of a pressure tank is easily translate into feet of head with this equation
2.31 feet of head = 1 psi
So for a typical residential pressure tank setting we’d get…
40 PSI = 92 feet of head
50 PSI = 115 feet of head
60 PSI = 140 feet of head ‘
Vertical lift refers to any elevation change between the top of the well and the next destination, like the pressure tank or storage tank that the pump is pushing water into. If the ground is flat, this number is “0”.
Finally, frictional loss is considered. Frictional loss is always going to occur in any long pipe run, the main goal is to minimize frictional loss. We’ll skip over this for now, as any RPS engineer can do a quick calculation to ensure that the pipe you’re using is big enough in diameter to not cause any issues.
All of the RPS 0.5HP water pumps fall into a total dynamic head range of 0-250 feet of head. Here’s a table of all the available models…
|
0.5HP RPS Water Pump Model |
Total Head Range |
Flow Rate Range |
|
05RPS05 |
Up to 250 feet of head |
4-8GPM |
|
07RPS05 |
Up to 200 feet of head |
8-13GPM |
|
10RPS05 |
Up to 150 feet of head |
11-18GPM |
|
25RPS05 |
Up to 125 feet of head |
20-31GPM |
Most residential well pump owners want their system to produce somewhere in the range of 10-25GPM, just to ensure that multiple bathrooms can operate at the same time.
Here’s an example of a total dynamic head calculation that would work for a 0.5HP water pump…
Well depth: 25 feet
Pressure Tank rating: 50PSI / 115 feet of head
Vertical Lift: 5 feet
25 feet + 115 feet + 5 feet = 145 feet
Usually, pump technicians will stay away from running up against the upper limit of a pumps ability range because the pump works too hard otherwise and pump lifetime may be shortened. For example, 145 feet is a bit too close to the 10RPS05 upper ability range of 150 feet of total head. Instead, we’d suggest a 07RPS05 in this case!
