The size whole house generator you need depends on the electrical loads you want to power, not just your home’s square footage. Generator sizing should account for the running watts of your appliances and systems, the extra power required to start large motors such as an air conditioner, and which loads may operate at the same time.
There is no single generator size for every 1,500-, 2,000-, or 3,000-square-foot house. Two homes of the same size can have very different backup power needs based on their HVAC systems, appliances, fuel types, and electrical usage.
Quick Takeaways
• Whole house generators are sized in kilowatts (kW).
• Generator size should be based primarily on electrical load, not square footage alone.
• Decide whether you want to power the entire home or only selected circuits.
• Central air conditioning, heat pumps, electric heat, well pumps, and other large loads can significantly affect generator sizing.
• Starting watts can be much higher than running watts for motor-driven equipment.
• Load management may allow some homes to use a smaller generator.
• A professional load calculation should determine the final generator size.
What Size Generator Do I Need for My House?
The right generator size depends on what you want to keep running during a power outage. A home that only needs essential circuits will require less generator capacity than a home that needs central air conditioning, cooking appliances, laundry equipment, and other high-demand appliances.
Your backup goal is a good place to start:
Home generator size should not be selected from this table alone. A load calculation provides a much more accurate answer because it looks at the actual equipment in your home.
How Do You Calculate Whole House Generator Size?
Whole house generator sizing starts by identifying the electrical loads the generator must support. The calculation should account for running wattage, motor starting requirements, and which electrical loads could operate at the same time.
1. List What You Want to Power
Start by deciding what needs backup power during an outage.
Common loads include:
Refrigerator and freezer- Lights and outlets
- Central air conditioning
- Heat pumps
- Electric water heater
- Well or sump pump
- Electric range
- Clothes dryer
- Internet equipment
- Medical equipment
- EV charger
You may want home backup for only essential circuits, or you may want a standby generator capable of supporting most normal household loads.
2. Find the Running Wattage
Running watts are the continuous power an appliance or electrical system needs while operating. Equipment nameplates and manufacturer specifications can provide voltage, amperage, or wattage information.
When voltage and amperage are known, basic electrical power can be calculated as:
Amps × Volts = Watts
For example, a 10-amp load operating at 240 volts represents 2,400 watts, or 2.4 kW.
3. Account for Starting Watts
Motor-driven equipment can require extra power for a few seconds when it starts. Air conditioners, refrigerators, pumps, and similar equipment can therefore require more generator capacity than their running wattage alone suggests.
Starting requirements matter because the generator must be able to handle that brief increase without being overloaded.
4. Determine the Maximum Expected Load
The final calculation should consider which loads are likely to operate at the same time. Simply adding the maximum wattage of every electrical device in the house can produce an unrealistic estimate.
A generator sizing calculation should instead consider total running watts, motor starting requirements, expected simultaneous loads, and any load-management equipment included in the system.
Running Watts vs. Starting Watts: What’s the Difference?
Running watts are the continuous watts an appliance needs while operating. Starting watts are the additional watts some motor-driven equipment needs briefly when starting.
Air conditioners, refrigerators, well pumps, and other equipment with motors can require more power at startup than during normal operation. A whole house generator must have enough power to handle the home’s running load and short starting loads.
For accurate generator sizing, use the electrical ratings or manufacturer specs for your home equipment. Do not rely on generic appliance wattage estimates.
What Appliances Use the Most Generator Power?
HVAC equipment and other large electrical appliances usually have the greatest effect on whole house generator size. The exact running and starting wattage depends on the specific equipment installed in the home.
High-demand loads commonly include:
The actual equipment ratings should be used when sizing a standby generator. Generic appliance wattage charts are useful for rough planning but should not replace the specifications of the equipment in your home.
How Does Air Conditioning Affect Generator Size?
Central air conditioning can affect generator size. This is because AC units have two loads. One is the running load. The other is the compressor starting load.
Homes with larger or multiple air conditioners may need considerably more generator capacity.
Air conditioning is especially important when sizing home generators in Houston. Losing central air conditioning during a long summer power outage can quickly make a home uncomfortable.
Generator sizing for central air conditioning should consider:
- AC running load
- Compressor starting requirements
- Number of AC systems
- Size and specifications of each system
- Soft-start equipment, when appropriate
- Load-management equipment
A standby generator does not necessarily need enough capacity to start every air conditioner and high-demand appliance at the exact same moment. Proper load management can control when some of those loads operate.
Whole-House Backup vs. Essential-Circuit Backup
You do not necessarily need to power every circuit in your home during an outage. Choosing between whole-home backup and selected essential circuits can significantly affect the generator capacity you need.
Essential-circuit backup might prioritize refrigeration, lighting, outlets, internet equipment, and selected HVAC equipment.
Whole-home backup provides more flexibility. However, whole-home backup does not necessarily mean every high-demand appliance must run simultaneously without any form of load management.
Can Load Management Reduce the Generator Size You Need?
Yes. Load management can sometimes lower the generator size needed. It does this by keeping high-demand appliances from running at the same time.
A load-management system can temporarily shed or delay selected electrical loads when generator demand becomes too high. Once enough capacity becomes available, the system can allow those loads to operate again.
Load management is very useful in homes with several large electrical loads. These loads do not need to run at the same time.
Is Generator Size Based on Square Footage?
Generator size is not based on square footage alone. Home size can provide some context, but actual electrical demand provides a more accurate basis for generator sizing.
Consider two 2,000-square-foot homes.
One home might have natural gas heat, a gas water heater, gas cooking, and one central air conditioner. Another could have electric heat, an electric water heater, electric cooking, an EV charger, and multiple HVAC systems.
The second home could have a much higher electrical demand even though both homes have the same square footage.
What Happens If a Whole House Generator Is Too Small?
An undersized whole house generator may not have enough capacity to support the electrical loads you want to run. Problems are most likely when several high-demand appliances operate together or when a large motor starts.
An undersized generator may:
- Become overloaded
- Trip or shed electrical loads
- Struggle with large motor starting loads
- Require you to limit which appliances operate
- Prevent some high-demand equipment from operating as expected
Correct generator sizing provides enough capacity for the planned backup loads without relying on guesswork during every power outage.
Can a Whole House Generator Be Too Big?
Yes. Bigger is not automatically better when choosing a whole house generator. An unnecessarily oversized generator can increase equipment cost without providing useful additional backup capacity.
The goal is not to buy the largest standby generator available. The goal is to choose enough capacity for the home’s expected electrical loads, motor starting requirements, and backup priorities.
Future electrical needs should still be considered. A homeowner planning to add another air conditioner, electric appliance, or other major electrical load may want that future demand included during generator sizing.
What Size Generator Do I Need for a 2,000-Square-Foot House?
You cannot accurately size a generator for a 2,000-square-foot house from square footage alone. The required capacity depends on the home’s HVAC equipment, fuel types, major appliances, electrical loads, and whether you want whole-home or selected-circuit backup.
Published generator size ranges based on square footage can provide a rough starting point. They cannot account for the major differences between individual homes.
A smaller home with electric heat and several high-demand appliances could require more backup power than a larger home that uses natural gas or propane for heating, cooking, and hot water.
A load calculation based on the home’s actual equipment provides a more reliable generator size.
How Does a Licensed Electrician Determine Generator Size?
A licensed electrician determines generator size by evaluating the electrical loads the standby generator will need to support. The electrician can also account for starting loads, simultaneous demand, the electrical panel, transfer switch, and load-management options.
Generator sizing may include reviewing:
- Desired backup loads
- Electrical service and panel
- HVAC equipment
- Motor starting requirements
- Expected simultaneous loads
- Natural gas or propane supply
- Automatic transfer switch
- Load-management equipment
- Planned future electrical loads
The generator itself is only one part of a home backup system. The transfer switch moves the home’s electrical load between utility and generator power. Load-management equipment can control high-demand appliances when generator capacity is limited.
Generator placement also needs to be considered before installation. The unit needs a suitable outdoor location that meets clearance requirements and keeps exhaust away from the home. Learn more about how far a generator needs to be from the house.
Fuel supply also matters. A natural gas or propane system must be capable of supplying the selected generator under the required operating conditions.
FAQs
Is a 22 kW generator enough to power a whole house?
A 22 kW generator may provide whole-home backup for some houses, but 22 kW is not enough for every home. The answer depends on HVAC equipment, major appliances, starting loads, simultaneous electrical demand, and load management.
Is a 24 kW generator enough for a 2,000-square-foot house?
A 24 kW generator may be enough for a 2,000-square-foot house, but square footage alone cannot answer the question. The home’s actual electrical loads and backup goals should determine whether 24 kW is appropriate.
How Many kW Does It Take to Run a Whole House?
There is no single kW rating required to run every whole house. Standby generator capacity depends on the home’s electrical demand, HVAC equipment, appliances, starting loads, and which systems need backup power.
Can a Whole House Generator Run Central Air Conditioning?
Yes. A properly sized whole house generator can run central air conditioning. Generator sizing must account for the AC system’s operating demand and the additional power the compressor may require when starting.
Do I Need a 20 kW or 24 kW Generator?
Choosing between a 20 kW and 24 kW generator requires comparing each generator’s capacity with the home’s calculated backup load. The extra 4 kW is useful only when the home’s electrical demand or future needs justify the additional capacity.
Does a Larger House Always Need a Larger Generator?
No. A larger house does not always need a larger generator. Fuel type, HVAC equipment, major appliances, EV charging, and backup priorities can affect generator size more than square footage alone.
Can Load Shedding Let Me Use a Smaller Generator?
Yes, load shedding may allow a smaller generator to support a home by preventing selected high-demand appliances from operating simultaneously. The load-management system temporarily reduces demand when the generator approaches its available capacity.
Does a Whole House Generator Power Everything at Once?
Not necessarily. A whole house generator may supply the home’s electrical system while load-management equipment controls when certain high-demand appliances operate. The exact setup depends on generator capacity, transfer equipment, electrical loads, and system design.
Need Help Sizing a Whole House Generator in Houston?
The right whole house generator should match your home’s electrical needs. Buying the biggest generator available is not the goal.
Right Touch Electrical can evaluate your electrical panel, HVAC equipment, major appliances, backup priorities, and expected loads before recommending generator capacity. We can then handle the generator installation, transfer equipment, and electrical work needed for dependable home backup power in the Houston and Pasadena area.
It’s how Right Touch Electrical brings quality with a master’s touch to generator installation throughout the Houston area.
