When the power goes out, most homeowners don't want to think about extension cords, portable generators, or deciding which appliance gets power next. A properly sized whole-house standby generator can automatically provide backup power and keep important equipment running during an outage.
The difficult question is deciding what size generator you actually need.
Is 13kW enough? Should you move up to 18kW or 22kW? Would a 26kW generator make more sense?
The answer depends less on the square footage of your home and more on what you expect the generator to power.
Generator Size Is About Electrical Load, Not Just Square Footage
You'll often see generator recommendations based entirely on home size. Square footage can be a useful starting point, but it isn't enough to properly size a standby generator.
Two 2,500-square-foot homes can have completely different electrical requirements.
One might have:
- Natural gas heat
- Gas water heater
- Gas range
- One central air conditioner
The other might have:
- Two heat pumps
- Electric water heater
- Electric range
- Electric dryer
- Well pump
- Pool equipment
Those homes shouldn't automatically receive the same generator simply because they're the same size.
A better approach is to identify the equipment you want available during an outage and calculate both its running and starting requirements.
Running Load vs. Starting Load
This is one of the most important concepts in generator sizing.
An appliance may require a relatively modest amount of electricity while operating but considerably more power for a short period when its motor starts.
Air conditioners, heat pumps, well pumps, refrigeration compressors and other motor-driven equipment are common examples.
That means a generator must do more than handle the home's normal running load. It also needs enough capacity to deal with large loads starting without causing excessive voltage drop or overloading the generator.
This is especially important if maintaining air conditioning is one of your priorities.
What Size Standby Generator Should I Consider?
Residential standby generators are available in numerous capacities. Briggs & Stratton's PowerProtect lineup, for example, includes options in the 13kW, 18kW, 22kW and 26kW range.
Here's a simple way to think about the different sizes.
13kW Standby Generator
A 13kW generator can be an excellent choice when the objective is protecting important household loads rather than operating every electrical appliance simultaneously.
Depending on the home's actual electrical requirements, those loads could include lighting, refrigerators, internet equipment, a gas furnace blower and selected household circuits.
Homes with larger air conditioners, electric heating or numerous high-demand appliances require more careful evaluation.
18kW Standby Generator
An 18kW generator provides additional flexibility and can make sense for homeowners who want to maintain more household equipment during an outage.
The additional capacity becomes particularly useful when central HVAC equipment, pumps or several appliances need to operate.
22kW Standby Generator
Moving into the 22kW range provides considerably more capacity for larger residential loads.
A 22kW generator may be appropriate for homes where maintaining central air conditioning along with normal household appliances is a priority.
However, the electrical specifications of the HVAC equipment still need to be considered. A large compressor can have significant starting requirements even when its normal running demand appears manageable.
26kW Standby Generator
A 26kW residential standby generator provides additional capacity for larger homes and heavier electrical loads.
This size becomes especially interesting for homes with large central air conditioners, multiple HVAC systems, pumps, pools or several major appliances.
Briggs & Stratton's 26kW PowerProtect models are specifically designed with substantial motor-starting capability, making them worth considering for homes with large compressor loads.
What Appliances Do You Want During an Outage?
Before selecting a generator, make a list of what you consider essential.
Start with items such as:
- Refrigerator
- Freezer
- Lights
- Internet equipment
- Central air conditioner
- Heat pump
- Furnace blower
- Well pump
- Sump pump
- Water heater
- Microwave
- Electric range
- Washer
- Dryer
- Pool equipment
Then separate them into two groups.
The first group should contain equipment that absolutely needs to operate.
The second should contain equipment that would be convenient but isn't essential.
This simple exercise can sometimes prevent homeowners from buying considerably more generator than they actually need.
Don't Forget Your Air Conditioner
HVAC equipment deserves special attention when sizing a standby generator.
A central air conditioner contains a compressor motor. When that compressor starts, its electrical demand can briefly be much higher than its normal operating demand.
If you're sizing a generator to operate central air, information from the equipment nameplate becomes important.
Useful specifications can include:
- Voltage
- Minimum Circuit Ampacity (MCA)
- Maximum Overcurrent Protection (MOCP)
- Rated Load Amps (RLA)
- Locked Rotor Amps (LRA)
The exact information available varies by equipment.
If your goal is to keep a 3-ton, 4-ton or 5-ton air conditioner operating during an outage, don't simply assume a particular generator size based on tonnage alone.
Check the electrical characteristics of the actual HVAC equipment.
What About Heat Pumps?
Heat pumps require additional consideration because they provide both cooling and heating.
During cold weather, some systems may also use electric auxiliary or emergency heat.
Electric resistance heat can represent a very large electrical load.
A generator capable of operating the heat pump compressor doesn't automatically mean it can operate every stage of electric backup heat.
This is one reason professional load calculations are particularly important for all-electric homes.
Natural Gas vs. Propane
Many residential standby generators can operate on either natural gas or liquid propane.
However, generator output can differ depending on the fuel being used.
When comparing generator capacities, don't assume the advertised maximum output is identical on both fuels. Review the manufacturer's specifications for the exact model and fuel.
Natural gas is attractive where utility gas service is available because the generator can remain connected to an existing fuel supply.
Propane can be a good solution for properties without natural gas service, but tank capacity and expected runtime need to be considered.
What Does an Automatic Transfer Switch Do?
A standby generator is normally paired with an automatic transfer switch.
When utility power fails, the system detects the outage, starts the generator and transfers selected electrical loads from utility power to generator power.
When utility service returns, the system transfers the home back to utility power and shuts down the generator.
Transfer-switch configuration is another part of generator selection that should be evaluated along with generator capacity.
Should I Buy a Larger Generator Than I Need?
Some reserve capacity can be useful, particularly if you expect to add electrical loads in the future.
But bigger isn't automatically better.
An oversized generator can cost more to purchase and install, while an undersized generator may not reliably support the equipment you expect it to operate.
The objective is to select a generator with enough running and motor-starting capacity for the loads you actually intend to use.
Choosing Between 13kW, 18kW, 22kW and 26kW
Think about generator sizing as a progression.
A 13kW system may work well when you're primarily protecting essential loads.
An 18kW system provides more flexibility.
A 22kW system moves further toward whole-home coverage and larger HVAC loads.
A 26kW system provides additional capacity for larger homes, substantial HVAC equipment and multiple major loads.
Those are general descriptions—not substitutes for a load calculation.
Need Help Choosing a Briggs & Stratton Standby Generator?
ACUnitsForLess carries Briggs & Stratton residential standby generators for a range of home backup-power applications.
If you're unsure which size is appropriate, gather the electrical specifications from your HVAC equipment and make a list of the appliances you want available during an outage.
That information provides a much better starting point than square footage alone.
A properly selected standby generator isn't about buying the biggest generator available. It's about having the right amount of power available when your home needs it most.
Shop Briggs & Stratton Standby Generators at ACUnitsForLess.
Generator sizing, electrical connections, fuel-system requirements, placement and installation should be verified by qualified professionals and must comply with manufacturer instructions and applicable codes.
