What size generator do I need to run my house

What Size Generator Do I Need to Run My House?

When the lights go out and the power grid fails, having a backup generator can be a true lifesaver. A generator can keep your essential appliances running, provide heat or air conditioning, and keep your home comfortable during extended power outages. But choosing the right generator size for your home can be a daunting task.

In this guide, we will delve into the intricacies of determining the size of the generator you need to effectively power your house during blackouts. Whether you’re considering a standby generator or a portable one, we’ve got you covered.

Why Do You Need a Generator?

Before we dive into the technical details of generator sizing, it’s essential to understand why you need one in the first place. Power outages can occur for various reasons, from natural disasters like hurricanes and snowstorms to equipment failures and grid overloads. Having a generator ensures that you can:

  1. Maintain Essential Functions: Keep your lights, heating, cooling, and refrigeration systems operational.
  2. Protect Your Home: Prevent frozen pipes, mold growth, or food spoilage due to prolonged outages.
  3. Stay Connected: Power your communication devices and stay in touch with loved ones during emergencies.
  4. Ensure Medical Devices: Keep life-saving medical equipment running, if needed.
  5. Enhance Security: Keep security systems and alarms active, deterring potential threats.

Generator Basics: Types and Fuel Sources

Generators come in various types, each suitable for different applications. Common generator types include:

  1. Portable Generators: These are versatile, smaller generators that can be moved around. They’re great for powering specific appliances or providing backup during camping trips or small power outages.
  2. Standby Generators: Also known as whole-house generators, these are permanent fixtures that automatically kick in when the power goes out. They can power your entire home seamlessly.
  3. Inverter Generators: These generators are known for their fuel efficiency and clean power output, making them suitable for sensitive electronics.

Generators also run on different fuel sources:

  1. Gasoline: Portable generators often use gasoline, making them easy to refuel but not the best for long-term outages due to limited fuel storage.
  2. Propane: Propane generators are known for their clean-burning characteristics and extended shelf life.
  3. Diesel: Diesel generators are fuel-efficient and durable, often used for larger generators.
  4. Natural Gas: If you have a natural gas supply, a natural gas generator can provide continuous power without worrying about refueling.

Determining Your Power Needs

One of the most crucial steps in choosing the right generator size is determining your power needs. You’ll need to calculate the total wattage required to run all the appliances and systems you want to power during an outage. Here’s how to do it:

  1. Make a List: Create a comprehensive list of all the appliances, lights, and devices you want to power during an outage. Don’t forget heating or cooling systems, well pumps, and sump pumps if you have them.
  2. Find the Wattage: Locate the power consumption (in watts) of each item on your list. You can usually find this information on the appliance’s label or in the user manual.
  3. Calculate Total Wattage: Add up the wattage of all the items on your list to determine your total power requirements. This will be measured in watts (W) or kilowatts (kW).
  4. Consider Starting Wattage: Some appliances, like refrigerators and air conditioners, require extra power to start up (starting wattage) before settling into their running wattage. Make sure to account for these spikes in your calculations.

Understanding Running and Starting Wattage

Different appliances have both running wattage and starting wattage. Here’s what you need to know:

  • Running Wattage: This is the continuous power a device needs to operate once it’s up and running. For example, a 60-watt light bulb has a running wattage of 60W.
  • Starting Wattage: Some appliances, like refrigerators or air conditioners, require extra power when they start up. This is called starting wattage or surge wattage. It’s usually higher than the running wattage but only lasts for a few seconds.

When sizing your generator, you should consider both running and starting wattage to ensure your generator can handle the initial surge.

Generator Size Guide

Now that you have a list of your power requirements, it’s time to choose the right generator size. Generators are typically rated in watts (W) or kilowatts (kW). Here’s a general guide to help you select the appropriate size:

  • 1,000-5,000W (1-5kW): These generators are suitable for running a few essential appliances or lights. They’re often portable and ideal for camping or small outages.
  • 5,000-10,000W (5-10kW): This range can power more appliances, including refrigerators, sump pumps, and some heating/cooling systems. It’s suitable for small to medium-sized homes.
  • 10,000-20,000W (10-20kW): These generators can power most of your essential appliances and systems, including well pumps, larger HVAC units, and more. They are suitable for medium to large homes.
  • 20,000+W (20kW+): Whole-house generators in this range can power an entire home, including heavy-duty appliances like electric ranges and central air conditioning systems. They are ideal for large homes or properties with high power demands.

Generator Sizing Examples

Let’s explore a couple of scenarios to help you understand generator sizing better:

Scenario 1: Small Homeowner

Suppose you have a small home with the following essentials:

  • Refrigerator (800W)
  • Sump Pump (750W)
  • Lights (300W)
  • Furnace Fan (750W)
  • Total Running Wattage: 2,600W

You’ll need a generator with at least 2,600 running watts plus additional starting wattage for appliances like the refrigerator and sump pump. A 3,000-4,000W portable generator should suffice.

Scenario 2: Medium Homeowner

For a medium-sized home with more appliances:

  • Refrigerator (800W)
  • Sump Pump (750W)
  • Lights (300W)
  • Furnace Fan (750W)
  • Well Pump (1,000W)
  • Central Air Conditioning (3,000W)
  • Total Running Wattage: 6,600W

You’ll need a generator with at least 6,600 running watts and additional starting wattage for appliances like the well pump and central air conditioning. A 7,500-9,000W standby generator would be a suitable choice.


Selecting the right generator size for your home is a critical decision. It ensures that you’ll have reliable backup power during outages, keeping your family safe and comfortable. By understanding your power needs and considering factors like running and starting wattage, you can make an informed choice.

Don’t forget to consult with a licensed electrician or generator installer to ensure proper sizing and installation, providing peace of mind during emergencies.

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