What Size Generator Do I Need for My Home?
Choosing the right generator size is crucial. Too small and you can't power essential systems. Too large and you waste money on unused capacity. This guide helps you calculate the perfect size for your East County home.
Quick Sizing Recommendations
For most San Diego East County homes, here are general generator size recommendations based on home size and coverage needs:
| Home Size | Essential Only | Whole House |
|---|---|---|
| Under 1,500 sq ft | 10-13 kW | 14-16 kW |
| 1,500–2,500 sq ft | 13-16 kW | 18-22 kW |
| 2,500–3,500 sq ft | 16-18 kW | 22-24 kW |
| Over 3,500 sq ft | 18-22 kW | 24-26 kW |
These are starting points. Your actual needs depend on specific appliances, AC system size, and whether you have high-draw equipment like well pumps. Keep reading for detailed calculations.
Understanding Starting Watts vs Running Watts
This is the most important concept in generator sizing. Many appliances require significantly more power to start than to run continuously:
- •Running Watts: Power required for continuous operation
- •Starting Watts: Extra power surge when appliance first turns on (typically 2-3x running watts)
Your generator must handle the highest possible starting surge while running other appliances. This is why proper sizing matters—an undersized generator trips breakers when your AC compressor kicks on.
Common Appliance Wattage Chart
Use this chart to add up the wattage of appliances you want to power during an outage:
| Appliance | Running Watts | Starting Watts |
|---|---|---|
| Central AC (3 ton) | 3,500 | 7,000 |
| Central AC (4 ton) | 4,500 | 9,000 |
| Central AC (5 ton) | 5,500 | 11,000 |
| Well Pump (1 HP) | 1,000 | 3,000 |
| Well Pump (2 HP) | 2,000 | 6,000 |
| Refrigerator | 200 | 600 |
| Electric Water Heater | 4,500 | 4,500 |
| Electric Range/Oven | 3,000 | 3,000 |
| Electric Dryer | 5,000 | 5,000 |
| Furnace Fan | 500 | 1,500 |
| Sump Pump | 800 | 2,000 |
| Lighting (10 LED bulbs) | 100 | 100 |
| TV & Electronics | 500 | 500 |
| Medical Equipment (varies) | 100-500 | 100-500 |
Air Conditioning: The Critical Factor
For East County homes, air conditioning is typically the largest electrical load. During PSPS shutoffs in summer and fall, you'll want AC capability:
- •2-3 ton AC: Minimum 16 kW generator for whole-house coverage
- •4 ton AC: Minimum 20 kW generator for whole-house coverage
- •5+ ton AC: 22-26 kW generator recommended
Check your AC unit's data plate for tonnage, or look at your monthly SDG&E bills for kWh usage during summer months.
Well Pump Considerations
Many East County properties in Julian, Ramona, and Alpine rely on private wells. Well pumps have high starting surges that affect generator sizing:
Well Pump Sizing Guide
- • 1/2 HP pump: Add 2,000 watts to generator requirement
- • 1 HP pump: Add 3,000 watts to generator requirement
- • 2 HP pump: Add 6,000 watts to generator requirement
- • 3 HP pump: Add 9,000 watts to generator requirement
Soft-start controllers can reduce starting surge by 50-70%. See our well pump generator sizing guide.
Step-by-Step Sizing Calculation
Follow these steps to calculate your minimum generator size:
- 1List all appliances you want to power during an outage
- 2Add up running watts for all appliances
- 3Identify highest starting watts appliance (usually AC or well pump)
- 4Calculate: (Total running watts) + (Highest starting watts) = Minimum generator watts
- 5Add 20% buffer for safety margin and future needs
Example Calculation: 2,500 sq ft East County Home
- • 4-ton central AC: 4,500 running / 9,000 starting
- • 1 HP well pump: 1,000 running / 3,000 starting
- • Refrigerator: 200 running / 600 starting
- • Lights, electronics, furnace: 1,500 running
- • Electric water heater: 4,500 running
Total running: 11,700 watts
Plus AC starting surge: 11,700 + 9,000 = 20,700 watts
Plus 20% buffer: 20,700 × 1.2 = 24,840 watts (25 kW)
Recommendation: 24-26 kW Generac generator
Get Professional Sizing Assistance
While this guide provides a solid starting point, a professional load calculation ensures you get exactly the right generator size. Our free on-site assessment includes detailed analysis of your electrical panel, appliances, and backup power goals.