How Big Does a Home Generator Actually Need to Be

Ask three contractors about generator sizing and you will get three answers. After collecting quotes for our own install, I found the honest answer is a spreadsheet, not a rule of thumb.

Start with the essential loads: refrigerator, freezer, well or sump pump, furnace blower, internet gear, and lighting for two rooms. That usually lands between 3,000 and 5,000 running watts for an average house. Add the biggest motor's starting surge, which can triple its draw for a second, and you have your floor.

The temptation is to size for everything, including the air conditioner and the electric water heater. That can double the cost of the unit and the fuel line. The compromise most neighbors landed on is a mid-size unit plus a load-shedding transfer switch that prioritizes circuits automatically.

Before you talk to any salesperson, run your own numbers with the worksheets over at Generator for House. Walking in with a load list changes the conversation completely: quotes got tighter and the upsells stopped.

Our final choice was an air-cooled whole house generator at 14 kW with an automatic transfer switch, sized to essentials plus the fridge circuit, and it has carried two outages since without a hiccup.