Well & Sump Pump FAQs

If you’re new to generator sizing overall, you may want to start with the Home Generator Sizing Guide or the General Generator FAQs, then come back here to dial in your pump loads.

What size generator do I need to run a well pump?

The required generator size depends on the horsepower (HP) of your pump, the motor type (2-wire vs. 3-wire), and what else is running at the same time. Typical residential well pumps range from 1/2 HP to 1 HP.

General estimates:

• 1/2 HP well pump: ~1,000 W running, 2,000–4,000 W starting
• 3/4 HP well pump: ~1,500 W running, 3,000–5,000 W starting
• 1 HP well pump: ~2,000 W running, 4,000–6,000 W starting

Pumps often draw 2–3× their running watts at startup. That short surge is what determines whether your generator is large enough.

For a typical 1/2–1 HP well pump, a generator in the 4,000–7,500 W range is often sufficient, depending on what else is running at the same time. Larger homes, higher HP pumps, or longer wire runs may require a 7,500–10,000 W portable or a standby system.

To see how your well pump fits into the bigger picture, plug it into the generator sizing calculator along with your other loads.

Can a portable generator run a well pump?

Yes—most portable generators in the 4,000–7,500 W class can run a typical residential well pump, as long as:

• You’re not simultaneously starting other big motor loads.
• The generator has adequate surge capacity.
• The pump’s electrical circuit is connected via a transfer switch or interlock.

If you have a larger 1 HP pump, older equipment, or long wire runs (which increase starting demand), a larger 7,500–12,000 W portable may be more reliable.

How many watts does a typical well pump use?

It varies by motor type and HP rating, but these ranges cover most homes:

• Running watts: ~700–2,000 W
• Starting watts: ~2,000–6,000 W

The best way to know for sure is to check the pump’s nameplate or control box. If it lists FLA (full-load amps) and LRA (locked-rotor amps), you can convert to watts:

Watts = Amps × Volts

Example: a pump with 8 A FLA at 240 V uses roughly 1,920 W running.

Can a sump pump and well pump run on the same generator?

Yes, but only if the generator can handle the combined starting load. Sump pumps also have significant inrush currents, although typically lower than well pumps.

Typical sump pump ranges:

• 1/3 HP: 600–800 W running, 1,300–2,500 W starting
• 1/2 HP: 800–1,200 W running, 2,000–3,500 W starting

If both pumps start at the same time, the generator must handle:

• Well pump surge (2,000–6,000 W)
• Plus sump pump surge (1,300–3,500 W)

This is why many homes rely on a 7,500–12,000 W portable or a right-sized standby unit when both pumps are mission-critical.

What size generator do I need for a well pump, sump pump, and fridge?

A very common “essentials-only” setup is:

• 1/2–1 HP well pump
• 1/3–1/2 HP sump pump
• Refrigerator/freezer

In many cases, a generator in the 7,500–10,000 W range works well for this combination, as long as:

• The pumps don’t start at the exact same moment.
• You’re not adding a major load (like a large AC or electric water heater).
• Your transfer switch wiring keeps these circuits isolated and safe.

Can I run a well pump directly off an extension cord?

No. Well pumps are hard-wired appliances and should not be connected with an extension cord.

To run a well pump from a generator, you need a transfer switch or interlock so the pump circuit can be powered safely without backfeeding the utility lines. For an overview of your options, see Transfer Switch vs. Interlock.

Your electrician will make sure the neutral, grounding, and bonding requirements are correct for your generator type. For broader generator safety guidance, including carbon monoxide precautions, see the U.S. Consumer Product Safety Commission’s portable generator safety information .

Does starting surge increase with pump age or wiring distance?

Yes—both can increase the current required at startup.

• Aging pumps often draw higher inrush current as bearings wear and efficiency declines.
• Longer wire runs to deep-well pumps add resistance, which can increase the starting VA the generator must supply.

If your well pump is older than about a decade or has a very long wiring run, lean toward the higher end of generator sizing ranges or ask an electrician to confirm the load.

What about jet pumps?

Jet pumps (commonly used in shallow wells) tend to have similar wattage requirements to submersible pumps of the same horsepower. A standard 3/4 HP jet pump often needs:

• 1,000–1,600 W running
• 3,000–4,500 W starting

If your home uses a jet pump for both water supply and pressure boosting, factor that load into your generator plan just like a submersible well pump.

To estimate total household load—including your well pump—try the generator sizing calculator.

← Back to all FAQ topics