Keeping the refrigerator, lights, internet equipment, and selected outlets powered requires a different plan than backing up every circuit in the house. The right standby generator size depends on the loads you intend to use when utility power fails, not square footage alone.
Your main breaker rating doesn’t determine which generator to buy. It shows the maximum capacity of the home’s electrical service, while generator sizing depends on the equipment operating at one time and the extra power motors need at startup.
Choose What Must Stay on During an Outage
Start by deciding whether you want selected-circuit or whole-home backup. The first option keeps specific necessities powered, while the second accommodates a broader set of household systems and requires careful management of larger loads.
Make a preliminary list that separates items that must run from those that can wait. This prevents you from paying for unused capacity or overlooking a system that matters during an extended loss of power.
Organize your list into three groups:
- Must Stay On: Refrigeration, essential lighting, internet equipment, selected outlets, medical equipment where applicable, and a sump pump.
- Comfort and Safety Loads: Heating or cooling equipment, garage access, security equipment, and hot-water needs.
- High-Demand Loads: Central air conditioning, electric heat, electric water heaters, cooking equipment, clothes dryers, and other major appliances.
Residential standby generators commonly range from 10 kW to 22 kW. A 10 to 14 kW unit often supports selected necessities in a mid-sized home, while a 20 to 22 kW generator can support a larger home with central air conditioning operating. These are preliminary ranges, not substitutes for evaluating the equipment in your home.
Whole-home backup doesn’t necessarily mean every large appliance should operate simultaneously. A clear plan identifies which heavy loads must remain available and which can stay off during a storm.
Estimate Operating Demand, Startup Demand & Headroom
Running watts measure the power an appliance or system uses while operating. Starting watts, also called surge watts, measure the higher demand some motor-driven equipment creates briefly at startup. Air conditioners, pumps, refrigerators, and some heating equipment can produce this surge.
For a preliminary estimate, record each intended load’s operating wattage from its nameplate, owner documentation, or manufacturer specifications. Then identify the highest startup figure among the motor-driven items you expect to use.
A common planning method uses three steps:
- Add the running watts of all intended loads.
- Add the single highest starting-watts figure.
- Multiply the result by at least 1.25 to provide capacity headroom.
For example, a plan with 8,000 watts of operating demand and one motor requiring 3,000 watts at startup totals 11,000 watts. Multiplying 11,000 by 1.25 produces a preliminary minimum capacity of 13,750 watts, or 13.75 kW. Final equipment selection still depends on the generator’s rated output, the home’s electrical configuration, and the management of major loads.
This method is more useful than sizing by the main breaker because it focuses on the largest combined demand. A written worksheet also highlights practical choices, such as delaying an electric water heater or cooking appliance while the cooling system starts.
Account for Alabama Weather & Home Systems
Alabama storm readiness involves more than powering lights and a refrigerator. Summer heat and humidity can make cooling a priority, while winter conditions change heating needs. The systems your household relies on in these conditions should guide the generator plan.
Air conditioning, electric heat, well pumps, electric water heating, and cooking equipment can substantially change the required capacity. An air-cooled generator in the 18 to 26 kW range can typically serve a 200-amp service when heavy loads are managed, but that service rating doesn’t automatically require a generator of this size.
Fuel planning also matters. A natural gas generator needs an available fuel supply and output rating suited to the planned electrical load. Site conditions, humidity, seasonal storms, and applicable building requirements also affect equipment selection and placement.
Keep the backup goal in view when comparing models. A smaller unit that reliably carries the systems you have identified is often more practical than assuming every electrical load must operate throughout a power interruption.
Plan for Safe Connection, Placement & Approval
Capacity is only one part of a safe standby-power system. A transfer switch isolates generator power from utility power when service is interrupted, helping prevent electricity from feeding back into utility lines.
Alabama Power requires customers to obtain approval from the inspecting city or county authority. It also prohibits operating a generator in parallel with its circuit without written authorization. The electrical connection, transfer equipment, and approval process should be planned together before equipment is selected.
Placement requires the same care. The Centers for Disease Control and Prevention advises operating generators outdoors at least 20 feet from the home, with exhaust directed away from doors, windows, and vents. A generator should never operate inside a home or garage, even with doors and windows open.
Where Jefferson County has jurisdiction, its Electrical Code is based on the 2017 National Electrical Code and groups generator permit applications by capacity: up to 10 kW, 10.1 to 25 kW, 25.1 to 50 kW, and above 50 kW. The county requires a licensed electrical contractor to perform electrical installations and maintenance. Permitting, inspection, site access, and manufacturer requirements should all be addressed before a unit is finalized.
Confirm the Load & Maintain the Generator
A useful generator consultation begins with the household’s backup priorities, not a model number. As an Authorized Cummins Generator Dealer, we review critical loads, motor startup demands, available fuel options, site conditions, and the electrical work required for a safe connection.
Our process includes generator selection, site preparation, delivery and installation, fuel and electrical line connections, pressure testing, and coordination with gas and power companies. We also guide customers through applicable site-selection and permitting requirements.
Maintenance remains important after installation. Routine inspections, oil changes, battery checks, and load testing confirm that the system is prepared to operate when storm conditions interrupt utility power. Our generator and electrical maintenance programs include priority service and waived dispatch service fees.
Bring a list of critical systems, high-demand equipment, and comfort priorities when comparing options rather than relying on square footage or a breaker label. For personalized load planning, installation, and generator service in Birmingham, Shepherd Electric Company provides support from selection through maintenance. Call us at (205) 479-5673 to discuss your backup-power needs.