Sump Pump (1/3 HP) Wattage for Generator Sizing
About the Sump Pump (1/3 HP)
A basement sump pump rated at 1/3 horsepower, the most common residential size for managing groundwater infiltration. Sump pumps are critical loads during storms and flooding events, which are often the same conditions that cause power outages. Without a sump pump running, basements can flood within hours during heavy rain, causing thousands of dollars in damage. The starting surge is significant relative to the running wattage. Many homeowners prioritize their sump pump as the single most important generator load during severe weather.
Generator Sizing for a Sump Pump (1/3 HP)
Running a sump pump (1/3 hp) by itself requires a generator with at least 1,625 W of capacity (2 kW), which includes a 25% safety margin. However, you rarely run a single appliance on a generator. When combined with other appliances, the sump pump (1/3 hp) contributes 800 W to the continuous running load and adds a potential 500 W starting surge gap when its motor starts.
The sump pump (1/3 hp) is an inductive (motor-driven) load with a starting surge of 1,300 W, which is 1.6 times its running wattage. This starting surge occurs for a fraction of a second when the motor first engages and must overcome inertia to begin rotating. Your generator must be capable of delivering this peak wattage even though it only lasts briefly. If the sump pump (1/3 hp) has the largest starting surge gap of any appliance in your generator load, its surge gap of 500 W will be the primary driver of your peak demand calculation. Avoid starting the sump pump (1/3 hp) at the same time as other large motor loads to prevent generator overload.
To determine the total generator size you need, use our interactive calculator to combine the sump pump (1/3 hp) with your other appliances. The calculator automatically handles the starting surge calculation and applies the 25% safety margin to give you an accurate recommendation. Alternatively, browse the scenarios below to see common generator setups that include the sump pump (1/3 hp).
Scenarios That Include Sump Pump (1/3 HP)
The following pre-calculated generator scenarios include the sump pump (1/3 hp) in their appliance list. Each scenario shows the total generator size needed for all appliances in the set, not just the sump pump (1/3 hp) alone. Click any scenario to see the full appliance breakdown.
| Scenario | Total Appliances | Running Watts | Recommended Size |
|---|---|---|---|
| Whole House Basic Coverage | 8 | 3,895 W | 7 kW |
| Full Disaster Preparedness Kit | 11 | 4,105 W | 7 kW |
Tips for Running a Sump Pump (1/3 HP) on a Generator
When running the sump pump (1/3 hp) on a generator, the most important consideration is the starting surge. Before starting the sump pump (1/3 hp), check that no other large motor-driven appliances are starting simultaneously. Stagger your startups: let the sump pump (1/3 hp) reach steady-state operation (usually within 1-2 seconds) before starting the next motor load.
If the generator struggles to start the sump pump (1/3 hp) (indicated by the generator bogging down, lights dimming significantly, or the appliance failing to start), it likely means the generator's peak surge capacity is insufficient. Try reducing other loads before attempting to start the sump pump (1/3 hp) again. If the problem persists, you may need a larger generator with more surge capacity.
Modern inverter generators handle motor starting surges particularly well due to their electronic power management. If you are purchasing a new generator specifically for loads that include the sump pump (1/3 hp), verify that the generator's peak (starting) wattage specification meets or exceeds the 1,300 W starting requirement plus the running wattage of all other connected appliances.
Sump Pump (1/3 HP) Wattage Compared to Similar Appliances
The following table compares the sump pump (1/3 hp) to other appliances in the water & plumbing category. Understanding relative power requirements helps you make informed decisions about which appliances to prioritize on your generator and where you might find opportunities to reduce your total load.
| Appliance | Running Watts | Starting Watts |
|---|---|---|
| Sump Pump (1/3 HP) (this appliance) | 800 W | 1,300 W |
| Well Pump (1/2 HP) | 1,000 W | 2,100 W |
| Well Pump (1 HP) | 2,000 W | 4,200 W |
| Sump Pump (1/2 HP) | 1,050 W | 2,150 W |
| Electric Water Heater | 4,500 W | — |
| Hot Water Recirculation Pump | 100 W | 200 W |
| Water Softener | 50 W | 100 W |
Frequently Asked Questions
How many watts does a sump pump (1/3 hp) use?
A sump pump (1/3 hp) uses approximately 800 watts of continuous (running) power during normal operation. It also requires 1300 watts of starting (surge) power when the motor first turns on, which is 1.6 times the running wattage. This starting surge lasts only a fraction of a second but your generator must be capable of delivering it.
What size generator do I need to run a sump pump (1/3 hp)?
To run a sump pump (1/3 hp) by itself, you need a generator rated for at least 1,625 W (2 kW), which includes a 25% safety margin above the starting wattage of 1300W. However, most people run additional appliances alongside the sump pump (1/3 hp), so your actual generator needs will be higher. Use our calculator to add your other appliances and get a comprehensive recommendation.
Can I run a sump pump (1/3 hp) on an inverter generator?
Yes, a sump pump (1/3 hp) can run on an inverter generator as long as the generator's peak (starting) wattage capacity meets or exceeds 1300 watts. Inverter generators handle motor starting surges well and provide clean power that is safe for the electronic controls found in many modern sump pump (1/3 hp) models. Verify the inverter generator's surge rating in the specifications.