Generator Sizing and Wattage Requirements Guide: What Size Generator Do I Need?

Josh Miller

Josh is a contributing writer to the site and former HVAC specialist.

Last Updated on May 26, 2021

When buying a generator, it’s essential to know the wattage requirements you’ll need for operating. Generators come in different sizes and models, and it’s important to choose the correct one.

You’ll need to make a list of the amount of energy your devices and home appliances use. This helps you understand your energy needs and ensure you purchase the best generator to meet them.

In case of a power outage, you need a generator that can power basic home appliances and products such as your fridge, house lights, and air conditioner. Some people just want a generator that can power a few devices, while others want one that can provide backup power for the entire house.

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Table of Contents

Why You Should Install a Generator

A generator provides the necessary backup power for your home in case of a power outage. Many Americans experience power outages once or twice a year. There are several reasons for an outage, but it’s not a cause for concern, and the average power outage can last around three hours.

In areas with extreme weather conditions, such as the Gulf coast, power outages can last for days. In these cases, power outages may cause serious problems, including spoiled food, flooded basements, and unbearable living conditions. Essential devices like dehumidifiers and basement sump pumps can also stop working, adding to the damage in your home. A backup generator can help avoid these occurrences by supporting the critical appliances in your house through the outage period.

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Three Main Types of Generators

When choosing the right size generator, it’s important to consider three different types. These are standby, inverter, and portable generators. Standby generators are generally larger than the other two, and they are the most common generator for homes.

1. Standby Generators

A standby generator is the most convenient for homeowners in case of an outage because it’s installed right outside the house and automatically starts working when the power goes out. This means you won’t have to go outside with a flashlight and manually start your generator. The only downside of standby generators is they aren’t portable. 

2. Portable Generators

These are smaller generators that are easy to carry. You can take them camping or traveling and use them to power any type of electronic device. You can also use a portable generator to power your home, although they are usually smaller than standby generators. The downside of portable generators is that you have to turn them on when a power outage occurs manually.

3. Inverter Generators

Inverter generators are similar to portable generators, but they also include an inverter. They are usually compact, light, and are convenient for camping or traveling. An advantage of inverter generators is that they produce cleaner and more sustainable energy.

The downside is that they are significantly more expensive than conventional generators because they use more advanced technology. Also, their maximum power output isn’t as high as that of traditional generators.

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How to Know Which Size Generator is Best for You

There’s a wide variety of generators on the market with different sizes. There are small, medium, and large generators. A generator that’s too small for your home won’t provide enough power. You don’t want to buy a generator that’s too big because you’ll pay for excess energy that you aren’t using.

To choose the right size, you need to learn to calculate the wattage requirements for your home.

How Much Backup Energy Do You Need?

Generator sizing requires knowing the amount of energy your home needs. You must also decide whether you want to power your whole house during a power outage or only essential home appliances and devices. The way to do this is to calculate your total energy requirements and choose a generator that supplies the appropriate wattage.

How Frequently Do You Experience Power Outages?

If you experience power outages very frequently, a larger standby generator might be the best option. Standby generators are the only kind that automatically kicks in when the power goes out.

If you live in an area that rarely experiences power outages, a large inverter generator or a portable generator might be sufficient for your needs. You can have it connected to your house and disconnect it to take with you on the road or camping.

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How to Calculate Total Energy Requirements

Generator sizing involves calculating the energy used by the devices and appliances in your home. You can do this on your own and get a decent approximation. However, many people seek help from a professional electrician to calculate their total energy needs.

1. Understanding Energy Labels

Energy is usually measured in watts or kilowatts. However, some home appliances or devices might have labels with energy consumption stated in amps or volts. Therefore, before calculating your total wattage requirements, you’ll need to understand these different terms and learn to convert them. This is a simple guide:

  • When volts and amps are given separately multiply them together to calculate the wattage: Volts * Amps = Watts
  • Kw or Kilowatts: 1 Kw = 1,000 Watts

2. Calculating Your Energy Needs

Make a list of all the home appliances and devices you want to power. Next to each item on the list, write down the power requirements in watts. Make sure you list both the starting wattage and the running wattage. The starting wattage, also called surge wattage, is the power a device uses to start working. It’s usually about 2-3 times higher than its running wattage.

Adding the starting wattage and running wattage of all devices and home appliances should give you an approximation of the energy you need. To be on the safe side, multiply the total amount by 1.25. This adds a safety margin of 25% extra energy to your total amount.

Choosing Your Generator

With more generator knowledge, you can make an educated choice and pick the perfect generator for your home. When in doubt, seek advice from professionals. A generator company can help you decide on the best type of generator for your home.

Consider the different types of generators before making a final choice. Solar generators have no running costs and are environmentally friendly. Unless you live on states that gets a lot of sun, the big concern is they rely on weather conditions to accumulate energy. However, a small solar generator can be a great investment in addition to a larger gasoline or propane generator for prolonged outages.

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