When the power goes out in Aiken, it is not just an inconvenience. Summer temperatures routinely exceed 95 degrees, and without air conditioning a home can become dangerously hot within hours. Winter ice storms can knock out power for days. A standby generator solves this problem, but only if it is sized correctly. Too small and it cannot handle your essential loads. Too large and you have overspent on equipment you will never fully use. This guide walks you through how generator sizing works so you can make an informed decision before you buy.
How Generator Sizing Works: The Load Calculation
Generator size is measured in kilowatts (kW), which represents how much electrical power the unit can produce continuously. To determine what size you need, you perform a load calculation: adding up the wattage of every appliance and system you want the generator to power, then accounting for startup surges that temporarily draw more power when motors kick on.
Every electrical device in your home has two power ratings that matter for generator sizing. The running watts (also called rated watts) is the continuous power the device consumes during normal operation. The starting watts (also called surge watts) is the brief spike of power required when a motor-driven device first turns on. Air conditioners, refrigerators, well pumps, and sump pumps all have significant starting surges that can be two to three times their running wattage.
A proper load calculation accounts for both values and ensures the generator can handle the worst-case scenario: multiple devices starting simultaneously during a power outage. Your electrician performs this calculation using your actual panel schedule and equipment specifications, not generic estimates from a website calculator.
Essential Coverage vs Whole-Home Coverage
The first decision you need to make is how much of your home you want to power during an outage. This choice has the biggest impact on generator size and cost.
Essential coverage powers only the circuits you designate as critical. A typical essential coverage setup includes the refrigerator, a few lighting circuits, the well pump (if applicable), the HVAC system, the garage door opener, and a few outlets for charging phones and running a computer. Essential coverage for most Aiken homes requires a generator in the 10 to 16 kW range. This approach uses a load management panel or transfer switch that connects only the selected circuits to the generator.
Whole-home coverage powers every circuit in your panel. When the power goes out, you may not even notice because everything in the house continues to operate normally: every light, every outlet, every appliance. Whole-home coverage for a typical Aiken home with central air conditioning requires a generator in the 20 to 26 kW range. Larger homes with multiple HVAC zones, electric water heaters, or high-demand appliances like electric ranges may need 30 kW or more.
Common Appliance Wattage for Aiken Homes
To give you a sense of how loads add up, here are the approximate wattages for common household equipment:
- Central air conditioner (3-ton) — 3,500 watts running, 7,000 watts starting
- Central air conditioner (5-ton) — 5,000 watts running, 10,000 watts starting
- Electric water heater — 4,500 watts running (no significant surge)
- Refrigerator — 150 watts running, 400 watts starting
- Well pump (1/2 HP) — 500 watts running, 1,500 watts starting
- Sump pump (1/3 HP) — 350 watts running, 1,000 watts starting
- Electric range/oven — 3,000 to 5,000 watts running
- Clothes dryer (electric) — 5,000 watts running
- Lighting (whole house LED) — 500 to 1,500 watts
- Garage door opener — 550 watts running, 1,100 watts starting
- Television and electronics — 200 to 500 watts
Notice that air conditioning dominates the load calculation. In Aiken's climate, the ability to run the AC during a summer power outage is typically the primary reason homeowners invest in a generator. If your home has a heat pump system, which most newer Aiken homes do, the wattage requirements are similar to a conventional AC system of the same tonnage.
Understanding kW Ratings
Standby generators are marketed with specific kW ratings, and understanding what those numbers mean helps you compare options. Most residential standby generators come in standard sizes: 10 kW, 14 kW, 16 kW, 20 kW, 22 kW, 24 kW, and 26 kW, with some manufacturers offering units up to 48 kW for large homes.
The kW rating represents the generator's continuous output capacity. A 22 kW generator can produce 22,000 watts of power on an ongoing basis. Most generators can also produce a brief surge above their rated capacity to handle motor startup loads, but you should not rely on surge capacity for sizing decisions.
Here is a general sizing guide for Aiken homes:
- 10 to 14 kW — Essential circuits only. Powers the AC, refrigerator, lights, well pump, and a few outlets. Good for smaller homes or budget-conscious buyers who want the basics covered.
- 16 to 20 kW — Essential circuits plus additional coverage. Can handle AC, kitchen appliances, multiple lighting circuits, and more outlets. A good middle ground for most Aiken homes under 2,500 square feet.
- 22 to 26 kW — Whole-home coverage for most homes. Powers everything including AC, electric water heater, kitchen appliances, lighting, and all outlets. The most popular range for homes between 2,000 and 4,000 square feet.
- 30 kW and above — Large homes with multiple AC zones, electric heating, pools, hot tubs, or workshops. Required when the total connected load exceeds what a 26 kW unit can handle.
Fuel Types: Natural Gas, Propane, and Diesel
Standby generators run on one of three fuel types, and your fuel choice affects sizing, cost, and convenience.
Natural gas is the most convenient option if your home is connected to a gas line. The fuel supply is unlimited since it flows through underground pipes that are rarely affected by storms. Natural gas generators never need refueling. The downside is that natural gas provides slightly less energy per unit of volume than propane, so a natural gas generator produces about 10 percent less power than the same unit running on propane. A generator rated at 22 kW on propane may produce about 20 kW on natural gas. Always check the rating for your specific fuel type.
Propane (LP gas) is the most common fuel choice in Aiken because many homes in the area are not connected to natural gas. Propane is stored in a tank on your property and delivers reliable performance. A 500-gallon propane tank can run a 22 kW generator for 5 to 8 days at 50 percent load, which covers most power outage scenarios in our area. The main consideration is ensuring your tank is large enough and scheduling regular propane deliveries.
Diesel generators are less common in residential applications but offer the highest fuel efficiency and longest engine life. They are more expensive upfront and require a dedicated fuel tank with secondary containment. Diesel generators make the most sense for very large homes or rural properties where fuel efficiency over extended outages is a priority.
Power Outages in the Aiken Area
Aiken County experiences power outages from several sources. Summer thunderstorms are the most frequent cause, typically producing outages lasting a few hours to a day. Ice storms, while less common, can cause extended outages of three to seven days as utility crews work to repair downed lines and damaged poles. Hurricane remnants that track inland through South Carolina can also cause multi-day outages, as Aiken experienced with several storms in recent years.
The frequency and duration of outages should factor into your sizing decision. If you experience multiple outages per year, a whole-home generator that lets life continue normally during every event may be worth the additional investment. If outages are rare and brief in your specific neighborhood, an essential-coverage unit may be perfectly adequate.
The Professional Load Calculation
Online generator sizing calculators provide rough estimates, but they cannot account for the specific equipment in your home, the age and efficiency of your HVAC system, the length of electrical runs from the generator to your panel, or local code requirements. A professional load calculation performed by a licensed electrician examines your actual panel schedule, identifies every circuit and its connected load, measures the starting and running requirements of your specific equipment, and produces an accurate sizing recommendation.
At Unity Power and Light, we perform load calculations for Aiken homeowners as part of every generator consultation. We will walk through your home, identify your priorities for power during an outage, calculate the exact load, and recommend a generator size that covers your needs without overspending on capacity you will never use. We handle the complete installation including the transfer switch, fuel connections, electrical tie-in, and all required permits and inspections.