Generator sizing is not simply a matter of matching the home’s electrical service rating. A useful design identifies what must operate during an outage, how much power those loads require, and which equipment can be delayed or managed. Oversizing adds equipment and fuel demand; undersizing can cause overloads, poor operation, and unreliable starting.
Build an Essential-Load List
Begin with safety and basic operation. Common priorities include the heating system, well or sump pump, refrigerator and freezer, selected lighting and receptacles, internet equipment, medical devices, and garage access. Businesses or home offices may need additional network, security, refrigeration, or process loads.
Separate true essentials from conveniences. Electric ranges, dryers, water heaters, central air conditioning, hot tubs, and EV chargers can change generator size considerably.
Understand Running and Starting Demand
Some equipment draws more power when starting than while running. Pumps, compressors, refrigerators, freezers, and air-conditioning equipment are common examples. A generator must handle both steady demand and the temporary starting demand when motors operate.
Equipment labels and manufacturer data help, but an electrician should evaluate actual circuit and starting requirements. Online wattage tables are estimates and may not represent your equipment.
Decide What Can Run at the Same Time
Sizing every connected load for simultaneous operation may create a larger system than the household needs. A practical outage plan can prevent high-demand appliances from operating together. Automatic load-management controls can also delay selected loads when generator capacity is needed elsewhere.
Ask which circuits are always available, which are managed, and what occupants must do during an outage.
Consider Heating, Cooling, and Water Systems
HVAC and water equipment often drive generator sizing. Identify the heating fuel, blower or pump requirements, air-conditioning equipment, well pump, sump pumps, septic equipment, and electric water heating. A home with gas heat may have very different electrical needs from an all-electric home.
Climate and outage season matter. The priority may be heat during winter, well water year-round, or cooling for health-sensitive occupants.
Account for Fuel and Expected Runtime
Generator output is only one part of resilience. Natural gas availability, propane storage, refueling logistics, fuel-system capacity, and expected outage duration affect the design. A large generator can consume more fuel even when the connected load is modest.
Fuel piping and tank sizing should be coordinated with qualified providers and the generator manufacturer’s requirements.
Review the Electrical Service and Transfer Equipment
The generator connects to the home through transfer equipment that prevents unsafe interaction with utility power. The electrician must review the service configuration, panel condition, grounding and bonding, generator connection, and supported loads.
Older or crowded electrical equipment may require corrective work before a generator can be integrated safely.
Avoid Sizing by Square Footage Alone
Homes of the same size can have completely different electrical loads. Appliance choices, heating fuel, pumps, workshops, EV charging, and occupant priorities matter more than floor area alone. A site-specific load assessment is more reliable than a generic “generator size by house size” chart.
Get a Generator Plan Based on Real Loads
Archimedes Electrical plans backup-power systems across Ulster County and the Hudson Valley. Request an Electrical Upgrade Estimate with your essential-load list, panel photos, fuel information, and outage priorities.