The right generator size depends on one main question: how much of your home do you want to power during an outage? Some homeowners want to keep just the essentials running, while others want the whole house to operate as if nothing happened. Your answer, combined with your home’s actual electrical loads, determines the size, which is why a proper load calculation is the reliable way to get it right.

Here is how to figure out what size generator you need.

Essential circuits versus whole-home

Generator sizing usually comes down to two approaches:

• Essential or partial coverage. A smaller generator powers the things you care most about during an outage, such as the furnace, refrigerator, sump pump, some lighting, and key outlets. This is more affordable and often uses a smaller unit.
• Whole-home coverage. A larger generator powers the entire home, including central air conditioning, electric appliances, and everything else, so life continues normally during an outage.

Deciding between these is the first step, because it has the biggest effect on the size and cost.

Home standby generator sizes

Air-cooled home standby generators commonly range from around 10 kW up to about 26 kW, with larger liquid-cooled units available for big homes. As a general sense:

• Smaller units cover essential circuits and modest homes.
• Mid-size units can run essentials plus some larger loads, often with load management.
• Larger units power whole homes, including central air, well pumps, and major appliances.

For example, a popular whole-home size can run a typical mid-size home with central air, a well pump, and major appliances together. Your specific loads determine where you land.

Why a load calculation matters

Rather than guessing, an electrician performs a load calculation to size your generator accurately. This adds up the loads you want to power, accounting for large draws like air conditioning, electric heat, well pumps, ranges, and any EV charging, and factors in that not everything runs at once. The result is a generator sized to actually meet your needs, so you neither run short during an outage nor overpay for capacity you will not use.

Load management can reduce the size you need

Modern standby systems often include load management, which intelligently prioritizes and sheds loads so a smaller generator can cover more of your home. For example, it might briefly reduce power to one large appliance while another runs, avoiding the need for a larger, more expensive unit. This can be a smart way to get the coverage you want at a lower cost.

Factors that affect your size

Several things influence the right size for your home:

• Square footage and overall electrical demand
• Central air conditioning and heating type
• A well pump or sump pump
• Major appliances like an electric range, dryer, or water heater
• EV charging
• Whether you want essential or whole-home coverage

The size generator you need depends on whether you want to power essential circuits or your whole home, combined with your actual electrical loads. Home standby units commonly range from about 10 to 26 kW, and the reliable way to choose is a load calculation that sizes the generator to your specific needs, sometimes with load management to reduce the required size. An electrician can assess your home and recommend the right size.

Stella Electric sizes and installs standby generators for homeowners across the Baltimore area and throughout Maryland, with flat-rate pricing and no overtime charges. We will run the numbers and recommend the right generator for your home. Financing is available on qualifying projects.