Three constraints, in order
Almost every generator on the market fails at least one of these, which is why the shortlist is short.
1. It must produce 240V. Residential well pumps are almost always 240V. A generator with 120V household sockets and a TT-30 RV outlet cannot supply one regardless of its wattage rating, and this is the single commonest mismatch people discover after buying.
2. It must reach a hardwired circuit. A well pump has no plug. Getting generator power to it means a transfer switch or an interlock, wired by an electrician — the comparison page covers the two legal routes.
3. It must survive the starting surge. A submersible pump motor starting under load is one of the hardest transient demands in a normal house, and it is the requirement that sets the size.
How much pump you actually have
Pump sizing varies enormously and rules of thumb are unreliable. The plate is the answer, and these are the ranges the plates typically fall into.
| Pump | Typical running | Generator to plan for |
|---|
| 1/2 HP jet or shallow well | Around 800-1,000 W | 5,000W class, with the rest of the list |
|---|
| 1/2 HP submersible | Around 1,000 W | 5,000-7,500W class |
|---|
| 1 HP submersible | Around 2,000 W | 7,500W class or above |
|---|
| 1.5 HP or a deep lift | Higher again | 9,500W and up |
|---|
Running figures are typical ranges for residential pumps. Starting draw is several times these numbers for a fraction of a second, which is what the generator has to absorb — read the plate on your own pump or its control box.
The margin rule that applies elsewhere on this site applies doubly here: add at least 20% to whatever your list totals, because pump plates are optimistic and old pumps draw more than new ones. The starting watts page has the underlying arithmetic.
What losing a well pump actually costs you
People underestimate this until it happens. On a well, an outage takes away drinking water, washing, dishes and flushing simultaneously — a pressure tank holds only a few minutes of use.
That makes water the most urgent thing on a rural outage list, ahead of the refrigerator. The water storage page covers the interim answer, and the rural property page works through what else fails at the same time.
The soft-start option
Worth knowing about before buying a much larger machine. Soft starters and pump control boxes that ramp the motor rather than slamming it on can substantially reduce the starting surge, which is the whole reason people oversize.
This is a job for the well contractor rather than a generic accessory, because it involves the pump control rather than the generator. But asking the question can be considerably cheaper than the next size up of machine.
Running pattern on a well
A well pump is an intermittent load — it runs to refill the pressure tank and then stops. That means it costs very little energy over a day and a great deal of surge capability at unpredictable moments.
The practical approach is to run the generator in blocks and fill containers during them, rather than trying to keep the system pressurized continuously. A couple of hours in the morning and evening covers a household comfortably and keeps fuel use sane — the well pump backup guide goes through the whole routine.
The short version
- 240V outlet or nothing. Check the control panel before the wattage.
- Read the pump plate. Half-horse and one-horse are different purchases.
- Budget the transfer switch. A well pump has no plug.
- Run in blocks and fill containers. The pump costs surge, not energy.
