SC By SCWS Team | February 2, 2026 | 11 min read
Backup Generator for Your Well Pump
When the power goes out, so does your water. Unlike homes on municipal water that may still have pressure during outages, well owners lose water the moment electricity stops flowing. No flushing toilets, no showers, no drinking water from the tap. For San Diego County rural homeowners, where PSPS (Public Safety Power Shutoffs) and fire-related outages are increasingly common, a backup generator isn't a luxury—it's a necessity. This guide covers everything you need to know about sizing, selecting, and connecting a generator to keep your well pump running.
⚡ Quick Reference: Generator for Well Pump
- • 1/2 HP pump: 4,000-5,000 watt generator minimum
- • 1 HP pump: 5,000-7,500 watt generator minimum
- • 1.5-2 HP pump: 7,500-10,000 watt generator
- • Transfer switch: Required for safe operation
- • Soft-start device: Can reduce generator size by 50%+
Understanding Well Pump Power Requirements
The biggest mistake people make when buying a generator for their well pump is underestimating the startup power requirement. Here's what you need to know:
Running Watts vs. Starting Watts
Well pumps use induction motors that need 3-5 times their running wattage to start. This "surge" or "starting wattage" only lasts 1-2 seconds, but your generator must handle it or risk:
- Voltage drops that prevent the pump from starting
- Generator overload and shutdown
- Damage to the pump motor from low voltage
- Tripping breakers or damaging the generator
Typical Well Pump Power Requirements
| Pump Size | Running Watts | Starting Watts | Min Generator Size |
|---|---|---|---|
| 1/3 HP | 800-1,000 | 2,400-3,000 | 3,500-4,000W |
| 1/2 HP | 1,000-1,400 | 3,000-4,200 | 4,500-5,000W |
| 3/4 HP | 1,400-1,800 | 4,200-5,400 | 5,500-6,500W |
| 1 HP | 1,800-2,400 | 5,400-7,200 | 7,000-8,000W |
| 1.5 HP | 2,400-3,000 | 7,200-9,000 | 9,000-10,000W |
| 2 HP | 3,000-3,600 | 9,000-10,800 | 10,000-12,000W |
💡 How to Find Your Pump's HP
Check the label on your pressure tank control box, the pump itself (if accessible), or your installation documentation. You can also check the pump's circuit breaker size—a 15-amp 240V breaker typically indicates a 1 HP pump or smaller.
Generator Types for Well Pumps
Portable Generators
Portable Generator Overview
✅ Advantages
- • Lower cost ($500-2,500)
- • Can be used for multiple purposes
- • Easy to move/store
- • No professional installation required
❌ Disadvantages
- • Manual setup required each time
- • Runs on gasoline (storage, refueling)
- • Louder operation
- • Must be started within hours of outage
Best for: Occasional outages (a few times per year), budget-conscious homeowners, those who travel frequently.
Standby (Permanent) Generators
Standby Generator Overview
✅ Advantages
- • Automatic operation (starts within seconds)
- • Runs on natural gas or propane (no refueling)
- • Quieter, more powerful options
- • Can power entire home, not just well
- • Increases property value
❌ Disadvantages
- • Higher cost ($3,000-15,000+ installed)
- • Requires professional installation
- • Permit may be required
- • Annual maintenance needed
Best for: Frequent outages, PSPS areas, those away from home often, properties without cell service for outage alerts.
Inverter Generators
Inverter Generator Overview
✅ Advantages
- • Clean, stable power (safe for electronics)
- • Quieter than conventional generators
- • More fuel-efficient
- • Lightweight and portable
❌ Disadvantages
- • Limited surge capacity (problematic for motors)
- • Higher cost per watt than conventional
- • May need soft-start device for well pump
Best for: Smaller pumps, those who also need to power sensitive electronics, noise-sensitive areas (with soft-start device for pump).
Connecting Your Generator Safely
Proper connection is critical for safety and protecting your equipment. Never attempt to backfeed power by plugging a generator into a wall outlet—this is illegal, dangerous, and can kill utility workers.
Transfer Switch Options
| Type | Cost | How It Works | Best For |
|---|---|---|---|
| Interlock Kit | $100-$300 | Slides over main breaker; prevents both being on | Budget option, DIY-friendly |
| Manual Transfer Switch | $200-$500 | Separate panel with switches for selected circuits | Portable generators, specific circuits |
| Automatic Transfer Switch (ATS) | $500-$2,000 | Detects outage, starts generator, switches automatically | Standby generators, seamless backup |
| Dedicated Outlet + Transfer | $300-$600 | Direct connection to well pump circuit only | Well pump-only backup |
⚠️ Critical Safety Warning
All transfer switch installations should be performed by a licensed electrician. Improper installation can result in electrical fires, equipment damage, or electrocution of utility workers. Always follow local codes and permit requirements.
240V vs. 120V Connection
Most residential well pumps operate on 240V power (two-pole breaker). This affects generator selection:
- 240V pumps require a generator with a 240V outlet (typically L14-30 or similar)
- Smaller generators may only have 120V outlets—verify before purchasing
- The transfer switch must be rated for 240V service
- Some older or very small pumps run on 120V—check your breaker panel
Reducing Generator Size with a Soft-Start Device
A soft-start device (also called a "pump saver" or "motor soft starter") can dramatically reduce your well pump's starting surge, allowing you to use a smaller, less expensive generator.
How Soft-Starters Work
Instead of the motor receiving full voltage instantly (causing the surge), a soft-starter ramps up voltage gradually over 2-3 seconds. This reduces starting current by 50-70%.
🔌 Soft-Start Impact Example
1 HP well pump without and with soft-start:
Without Soft-Start
7,200W Starting Surge
Requires 8,000W+ generator
With Soft-Start
2,500-3,000W Starting
4,000-5,000W generator works!
Soft-Start Device Costs
- Device cost: $150-$350 depending on HP rating
- Installation: $100-$200 (or DIY if electrically competent)
- Generator savings: Can save $500-2,000+ on generator size
- Additional benefits: Reduces pump wear, extends motor life, smoother operation
Popular brands include Pumptec, ICM Controls, and Franklin Electric SubStart. Match the device to your pump's HP rating.
Sizing for Whole-House vs. Well-Only Backup
Well Pump Only
If you only need to power your well pump during outages:
- Size generator for pump starting watts plus 20% buffer
- A 5,000-7,500W portable generator handles most residential pumps
- With soft-start: a 3,500-5,000W generator may suffice
- Fuel consumption is minimal since pump only runs when needed
Whole-House Backup
If you want to power more than just the well:
| Load | Running Watts | Starting Watts |
|---|---|---|
| 1 HP Well Pump | 2,000 | 6,000 (or 2,500 w/soft-start) |
| Refrigerator | 150-400 | 600-1,200 |
| Lights (10 LEDs) | 100-150 | Same |
| Sump Pump | 800-1,400 | 1,500-2,800 |
| Furnace Blower | 500-750 | 1,000-1,500 |
| Phone/Laptop Chargers | 50-100 | Same |
| TOTAL (example) | ~4,000 | ~10,000 |
For whole-house backup including well pump, refrigerator, some lights, and essential circuits: 7,500-12,000 watt generator recommended. Add soft-start to the well pump to reduce total starting requirement.
Generator Recommendations by Scenario
Budget Portable: Well Pump Only
Generator: 5,000-6,500W portable ($500-$1,000)
Add: Manual transfer switch or interlock kit ($150-$400 installed)
Optional: Soft-start device ($250-$400 installed) to reduce size to 4,000W
Mid-Range: Well + Essential Circuits
Generator: 7,500-10,000W portable or inverter ($1,000-$2,500)
Add: Manual transfer switch with 6-10 circuits ($400-$800 installed)
Recommended: Soft-start on well pump for headroom
Premium: Automatic Whole-House
Generator: 10-22kW standby ($3,000-$8,000 for unit)
Add: Automatic transfer switch + installation ($2,000-$4,000)
Fuel: Natural gas (if available) or propane tank (250-500 gallon)
Operating Tips for Well Pump Generators
During an Outage
- Start the generator before connecting load — Let it warm up for 2-3 minutes
- Turn off unnecessary circuits — Maximize power available for well pump
- Let the pressure tank fill — Don't run faucets while pump is cycling
- Limit water use — Fewer pump starts = less fuel consumption
- Monitor fuel levels — Never let generator run completely dry
Regular Maintenance
- Run monthly — 15-30 minutes under load keeps seals lubricated and battery charged
- Change oil — Follow manufacturer intervals (typically every 50-100 hours of use)
- Stabilize fuel — Add fuel stabilizer if storing gasoline more than 30 days
- Test transfer switch — Annual test ensures it works when needed
- Check battery — Standby generators have starter batteries that need replacement
Your Pressure Tank Is Your Battery
Here's a tip many well owners don't realize: your pressure tank stores usable water even when the pump isn't running. A larger pressure tank means:
- Fewer pump starts per day (less fuel consumption)
- More water available between generator run cycles
- Reduced wear on pump and generator
If you're upgrading your backup power setup, consider upgrading to a larger pressure tank at the same time. A 50-80 gallon tank provides much more buffer than a standard 20-gallon tank.
Frequently Asked Questions
What size generator do I need to run my well pump?
Most residential well pumps need a generator with 3-5x the pump's running wattage to handle startup surge. A 1 HP pump (around 2,000 running watts) needs a generator capable of 6,000-10,000 starting watts. A 5,000-7,500 watt generator handles most residential well pumps, while a 10,000+ watt unit can run the pump plus other household loads.
Can I run my well pump with a portable generator?
Yes, portable generators can power well pumps if properly sized and connected. You'll need a transfer switch for safe connection—never plug a generator directly into an outlet (backfeeding). Portable generators work well for occasional outages but require manual setup and refueling.
Do I need a transfer switch for my well pump generator?
Yes, a transfer switch is required for safe generator operation. It isolates your home from utility power, preventing dangerous backfeeding that can injure utility workers. Options include manual transfer switches ($200-500), interlock kits ($100-300), and automatic transfer switches ($500-2,000+).
What's the difference between a standby and portable generator for well pumps?
Standby generators are permanently installed, start automatically during outages, and run on natural gas or propane. They cost $3,000-15,000+ installed but provide seamless backup. Portable generators cost $500-2,000, require manual setup, and run on gasoline. Portable works for occasional outages; standby is better for frequent or extended outages.
Why does my well pump need so much starting wattage?
Well pumps use induction motors that require 3-5x their running wattage to start. This startup surge lasts only 1-2 seconds but the generator must handle it. Using too small a generator causes voltage drops that can damage the pump motor. Soft-start devices can reduce startup surge by 60-70%.
Can I use an inverter generator for my well pump?
Yes, inverter generators work well for well pumps and provide cleaner power for sensitive electronics. However, ensure the inverter generator can handle the pump's starting surge—many inverters have limited surge capacity. Look for models specifically rated for motor loads or use a soft-start device on your pump.
How long can I run my well pump on a generator?
You can run your well pump on a generator as long as you have fuel and the generator is properly maintained. The pump itself doesn't run continuously—it cycles on to fill the pressure tank, then shuts off. Most households use the well pump for 1-3 hours total per day, so fuel consumption is manageable.
Will my pressure tank help reduce generator requirements?
Yes! A larger pressure tank reduces how often the pump starts, extending generator run time per tank of fuel. The tank stores pressurized water, so you have water available even when the pump isn't running. Larger tanks (50+ gallons) are especially helpful for generator backup situations.
Need Help With Your Well Pump Backup Power?
From sizing recommendations to soft-start device installation, Southern California Well Service can help you prepare for power outages. We can also upgrade your pressure tank for better generator performance or evaluate your pump's condition before the next outage season. Learn more about our pump services and maintenance programs.
