Imagine this: a summer night, the power flickers, and then… darkness. Your fridge hums to a halt, the movie on TV freezes on-screen, and a cold sweat forms as you realize the air conditioner has stopped. Power outages can be disruptive, but a home generator can be your knight in shining armor, ensuring your comfort and safety during these unexpected events.
But before you rush out and buy the first generator you see, choosing the right size is crucial. An undersized generator won’t power your essential appliances, while an oversized one can be a waste of money and fuel. This guide will equip you with the knowledge to select the perfect home generator size for your needs.
Understanding Your Power Needs
The first step is to identify the essential appliances you want to run during a power outage. Here are some common home appliances and their estimated wattages:
- Refrigerator: 600-800 watts
- Freezer: 400-800 watts
- Sump Pump: 750-1500 watts (consider the starting wattage, which can be higher)
- Furnace/Air Conditioner: 3500-5000 watts (startup wattage can be much higher)
- Well Pump: 1000-2000 watts (startup wattage can be much higher)
- Washer/Dryer: 1800-3500 watts (each)
- Microwave: 1000-1500 watts
- Television: 100-300 watts
- Computer: 200-1000 watts
These numbers are only general estimates. Certain appliances, particularly equipment with electric motors, can require significantly more power when they first start than they use while running.
The electrical configuration of your home also matters. Two similarly sized homes can have very different generator requirements depending on whether major appliances use electricity or natural gas, the size of the HVAC equipment, the presence of a well or sump pump, and other electrical loads.
Do the Math: Add Up Your Wattage Requirements
Adding up the wattage of the appliances and equipment you want to operate can provide a rough idea of how much backup power you may need.
It is important to account for both running wattage and startup wattage. Equipment such as air conditioners, pumps, refrigerators, and freezers can briefly draw considerably more electricity when their motors start.
For a permanently installed standby generator, however, appliance wattages should be treated as a starting point rather than the final sizing method. A professional load calculation can determine the electrical demand of your home and help identify the appropriate generator capacity.
Adding a Buffer: Safety Net for Unexpected Needs
It’s wise to add a buffer of 20-30% to your total wattage requirement. This extra capacity ensures your generator can handle unexpected loads or future appliance additions without overloading.
Here’s the Formula:
Total Wattage Requirement = Sum of Appliance Wattages (including surge wattages) x 1.2 (20% buffer)
Example Calculation:
Let’s say you want to run your refrigerator (800 watts), sump pump (1000 watts), and lights (500 watts) during an outage.
Total Wattage Requirement = (800 watts + 1000 watts + 500 watts) x 1.2 = 2300 watts x 1.2 = 2760 watts
Choosing Your Generator Size
Use this table as a starting point when comparing standby generator sizes. The right option for your home depends on how much of the house you want to power, your major electric appliances, and the results of a professional load calculation.
| Generator Size | Output | What It Could Mean for Your Home | Typical Installed Price Range* |
|---|---|---|---|
| 10 kW | 41 amps | A practical option if your main goal is to keep essential circuits running during an outage, such as your furnace, gas water heater, sump pump, well pump, refrigerator, freezer, lights, and general outlets. Load shedding modules can sometimes allow you to power additional circuits as well. | $11,500-$15,000 |
| 14 kW | 58 amps | A good middle-ground option if you want to power more of your home. It can be used for partial- or whole-home backup, often with load shedding modules for larger electric appliances or a transfer panel that limits which circuits are powered. | $14,000-$17,500 |
| 17-18 kW | 70-75 amps | Often a strong fit if you want whole-home backup. If your home is around 2,000 square feet or larger, or you have several high-demand electric appliances, load shedding modules may still be needed. | $16,500-$19,000 |
| 21-22 kW | 87-91 amps | Typically used when you want whole-home backup with enough capacity to avoid load shedding in many homes. Your home’s load calculation determines whether this size is the right fit. | $18,000-$28,000 |
| 22.5-24 kW | 93-100 amps | Typically used for whole-home backup when your electrical demand is higher. In many homes, this size can power the house without load shedding, depending on the results of the load calculation. | $18,000-$28,000 |
| 24-26 kW | 100-108 amps | Designed for homes with greater whole-home power needs. This may be a better fit if you have multiple large electric appliances or other higher-demand equipment. | $18,000-$28,000 |
| 25-28 kW | 104-116 amps | The largest option in this range and generally intended for homes with substantial electrical demand. A load calculation is used to confirm whether this level of capacity is necessary. | $18,000-$28,000 |
How to use this information: The goal is not simply to choose the largest generator. A professional load calculation determines how much power your home actually requires. In some cases, load shedding modules can reduce the generator size you need by temporarily managing selected high-demand appliances.
*Price ranges can vary based on the location and size of the home’s gas and electric utilities. Finished or unfinished basements and garages can also have a significant impact on installation pricing.
What Can a 10 kW Generator Power?
A 10 kW generator is the smallest option in this range and is commonly chosen by homeowners who want to prioritize essential circuits rather than power everything in the home at once.
Essential circuits may include:
- Furnace
- Gas water heater
- Sump pump
- Well pump
- Refrigerator
- Freezer
- Lighting circuits
- General receptacle circuits
With properly designed load shedding modules, a 10 kW generator may also be able to support more than these essential circuits by temporarily limiting power to selected high-demand equipment when necessary.
When Do You Need a Larger Whole-Home Generator?
Generators in the 14-18 kW range provide additional flexibility and may work as partial- or whole-home solutions depending on the home’s electrical demand.
Once you move into the 21-28 kW range, generators are most often used as whole-home systems. These larger capacities can frequently operate without load shedding devices, although the appropriate generator still depends on the home’s calculated load.
A larger generator is not automatically the better choice. A professional load calculation helps determine how much capacity your home actually requires. In some situations, strategically using load shedding modules can allow a homeowner to select a smaller generator while still maintaining the backup power they need.
What Affects Home Generator Installation Cost?
Generator capacity is only one factor that determines the total installation cost.
Pricing can vary depending on:
- Generator size
- Location of the generator
- Existing gas utility size and capacity
- Existing electrical service
- Distance between the generator and utility connections
- Whether the basement is finished or unfinished
- Whether the garage or other installation areas are finished
- Additional electrical or gas work required for installation
- Need for load shedding modules or other load management equipment
Additional Considerations
Fuel Type
Standby generators commonly use natural gas or propane. Available fuel sources and the capacity of the home’s existing gas system can affect both generator selection and installation requirements.
Transfer Switch
A transfer switch connects the generator to your home’s electrical system and safely transfers electrical loads from utility power to generator power during an outage.
Depending on the generator design, a transfer panel may also be used to control which circuits are powered.
Load Shedding Modules
Load shedding modules help manage high-demand electrical equipment. If the generator begins approaching its available capacity, selected loads can temporarily be disconnected so priority equipment continues receiving power.
This can sometimes allow a smaller generator to provide effective whole-home backup power without requiring homeowners to move to the next generator size.
Professional Load Calculation and Installation
Online wattage estimates can give you a general idea of your electrical needs, but proper standby generator sizing requires more than adding together appliance wattages.
A professional can evaluate your home’s electrical service, major appliances, HVAC equipment, pumps, and other loads before completing a load calculation. This helps determine which generator size and load-management strategy best fit your home.
Professional installation is also important to ensure the generator, transfer equipment, electrical connections, and fuel supply are properly configured.
Find the Right Generator for Your Home
The right home generator should provide the backup power you need without paying for unnecessary capacity. Whether you want to keep a few essential circuits operating or provide backup power throughout your home, generator sizing should be based on your home’s actual electrical demand.
The experts at All Comfort Services are here for all your electrical needs throughout Dane County. We offer repair and replacement of Generac generators and can help determine the appropriate generator size for your home.
For generator and electrical services you can trust in Dane County, contact the experts at All Comfort Services today.
