Well pump size by depth / 100 ft
Well pump size with water 100 feet down
With the pumping water level 100 feet below the wellhead, the pump lifts 100 feet and then pushes up to the switch's cut-out pressure: 239 feet of head at 40/60 psi, 216 at 30/50, before pipe friction. In Goulds' 10GS series the smallest motor that meets a 7 gpm one-bathroom demand at 40/60 is ¾ hp; at 30/50 it is ¾ hp.
At 100 feet the ½ hp pumps start to run short at higher pressure: the 10GS05 gives 7.5 gpm at 40 psi and is not rated at all at 60.
A ¾ hp 10GS07 covers a one or one-and-a-half bathroom house on either switch setting; two bathrooms on 40/60 call for the 1 hp model.
Which 10GS model meets each household demand
| Bathrooms | Pump flow needed | At 30/50 psi | At 40/60 psi |
|---|---|---|---|
| 1 | 7 gpm | 10GS07, ¾ hp (13.9 gpm at 30 psi) | 10GS07, ¾ hp (13.9 gpm at 40 psi) |
| 1½ | 10 gpm | 10GS07, ¾ hp (13.9 gpm at 30 psi) | 10GS07, ¾ hp (13.9 gpm at 40 psi) |
| 2–2½ | 14 gpm | 10GS07, ¾ hp (13.9 gpm at 30 psi) | 10GS07, ¾ hp (13.9 gpm at 40 psi) |
| 3–4 | 17 gpm | 10GS07, ¾ hp (13.9 gpm at 30 psi) | 10GS07, ¾ hp (13.9 gpm at 40 psi) |
Smallest model that delivers the flow at the cut-in pressure and is still rated at the cut-out pressure, read at the 220 ft column. Demand: Goulds peak-demand table. Pipe friction and any rise to the tank add to the depth — use the calculator for your pipe run.
The chart at 100 feet
Rated gallons per minute for each model at this depth, by the pressure rows of Goulds' chart (labelled PSI). A dash means the model is not rated there — either it cannot lift that far against that pressure, or the depth is shallower than its recommended range.
| Model | HP | 0 psi | 20 psi | 30 psi | 40 psi | 50 psi | 60 psi |
|---|---|---|---|---|---|---|---|
| 10GS05R | ½ | 12.4 | 6 | — | — | — | — |
| 10GS05 | ½ | 15.3 | 12.5 | 10.5 | 7.5 | — | — |
| 10GS07 | ¾ | — | 15 | 13.9 | 12.7 | 11.6 | 10.3 |
| 10GS10 | 1 | — | — | 15.6 | 14.7 | 13.9 | 12.8 |
| 10GS15 | 1½ | — | — | — | — | — | 15.7 |
| 10GS20 | 2 | — | — | — | — | — | 16 |
| 10GS30 | 3 | — | — | — | — | — | 16 |
Ratings: Goulds Water Technology, Model GS 5–25 GPM technical brochure B5-25GS (March 2012) — copy hosted by a retailer; the current Xylem brochure has no ratings tables — "Depth to Water in Feet/Ratings in GPM (Gallons per Minute)". Read at the next listed depth at or below 100 ft.
Reading this for your well
- Use the pumping level, not the static level. Water drops when the pump runs; the well driller's log or a pump test gives the pumping level. If you only know the static level, the difference can be tens of feet.
- Add the rise and friction. A tank uphill of the well adds its height; 14 gpm through 200 feet of 1¼-inch plastic pipe adds 7 feet, through 1-inch pipe 26 feet.
- Check the well's yield. A pump larger than the well can supply will draw it down. New York's health department suggests a well yield of at least 5 gpm for a home; a pressure or storage tank covers peaks above that.
- Match the tank. A 14 gpm pump on 40/60 needs about 54.3 gallons of pressure tank for a one-minute run — see 14 gpm tanks.