To run a typical electric hot water heater, choose a generator with at least 4,000 to 5,000 watts to handle the starting and running wattage requirements.
Choosing the right generator size for your hot water heater is crucial for emergency preparedness. This guide explains how to calculate your power needs and select the best generator.
Generator Size Requirements for Water Heaters
Most standard electric water heaters require 4,500-5,500 watts to operate. Tankless models may need 7,000-10,000 watts. Gas water heaters with electric ignition require less power (1,000-1,500 watts).
Common Water Heater Wattages
| Water Heater Type | Running Watts | Starting Watts |
|---|---|---|
| 40-50 gallon electric | 4,500-5,500 | 5,000-6,000 |
| Tankless electric | 7,000-10,000 | 8,000-12,000 |
| Gas with electric ignition | 1,000-1,500 | 1,500-2,000 |
Calculating Total Power Needs
When sizing a generator, consider all appliances you want to run simultaneously. Follow these steps:
- List all essential appliances (fridge, lights, etc.)
- Add their running wattages together
- Identify the appliance with highest starting watts
- Add starting watts to total running watts
Example Calculation
For a home with:
- Water heater (4,500W running)
- Refrigerator (700W running, 2,100W starting)
- Lights (500W total)
Total = 4,500 + 700 + 500 + (2,100 – 700) = 7,100W minimum generator size
Generator Recommendations
For most homes with electric water heaters, a 7,500-10,000 watt generator is ideal. Consider these options:
Standalone Water Heater Operation
A 5,000-7,500W generator can run a 40-50 gallon water heater alone. The Duraheat portable propane heater is a good alternative for supplemental hot water.
Whole House Backup
For water heater plus other essentials, choose 10,000-12,000W. The built-in gas heater options may provide more efficient alternatives.
Important Installation Considerations
Wiring Requirements
Most generators require professional installation. Key factors:
- Transfer switch vs. interlock kit
- Bonded vs. floating neutral
- Proper grounding
Fuel Efficiency
Larger generators consume more fuel. According to Generac, a 10,000W generator may use 0.75-1.5 gallons per hour under load.
Alternative Solutions
If generator size is impractical, consider:
- Gas tankless water heaters (lower power needs)
- Solar water heating systems
- Point-of-use electric heaters for critical needs
The U.S. Department of Energy provides additional guidance on efficient water heating options.
Maintenance Tips
To ensure reliable operation:
- Test generator monthly
- Rotate fuel supply
- Keep water heater elements clean
- Consider a generator maintenance contract
