Generators provide power to spaces and devices during blackouts or in areas where standard electrical service isn't available. Generators range from 800 watts to over 500,000 watts, and there are different types of generators for every need. When the question "What size generator do I need?" comes up, this guide will help you choose the best generator size for you.
How Much Generator Power Do You Need?
If you’re wondering “how big of a generator do I need?” what you really want to know is how much generator power or total wattage you need. To determine the best generators for home use, refer to the list and select which appliances and systems you want to power. For an exact wattage number, consult your appliance and systems manuals.
Remember that if an appliance has a motor, you will need to calculate the total wattage using the formula:
Running wattage (R) + Starting wattage (R x 3) = Total wattage needed
With this formula, you can figure out the approximate total wattage needs for each appliance with a motor. Items like light bulbs and coffeemakers, however, don’t need an extra boost of power when they’re turned on. For these items, you only need to be concerned about the running wattage.
Once you have those, a list of items you want to power and the wattages they need, add the numbers together to figure out what size generator would be right for you. The more appliances you want to use, the bigger generator you will need.
- Below is a list of approximate running wattage for various household appliances and technology:
Refrigerator/Freezer: 600 - 800
- Electric Range (one element): 2500
- Toaster: 1100 - 1700
- Microwave: 1200
- Hot Plate: 1250
- Coffeemaker: 400 - 800
- Electric Oven: 5000
- Television: 100 - 350
- Personal Computer: 500 - 2000
- Hair Dryer: 1200 - 1500
- Vacuum: 700 - 1400
- Space Heater: 1250
- Table Lamp: 150
Below is a list of approximate HVAC and system wattage needs:
Electric Furnace: 5000 - 25000
- Heater (radiant): 1300
- Central Air Conditioning: 2000 - 4000
- Water Heater: 3000 - 4500
- Water Pump: 1000 - 2000
- Window Air Conditioner: 600 - 1500
- Outdoor Lighting: 500 - 1000
- Sump Pump: 1500
Note: The power requirements in this guide are general examples and should not be used to calculate specific requirements. Refer to the user manuals that came with your appliances and tools for manufacturer-provided power requirements.
Understanding Starting, Running and Surge Wattage
The wattage or power your generator needs to produce will depend on the quantity and type of items or equipment you want to run. Before you can calculate your needs, you need to understand what starting wattage, running wattage and surge wattage are.
Your running wattage is the amount of electricity you need to keep the device running. As the name implies, your starting wattage is the amount of electricity you need to start the device. On average, the amount of power you need to start a device is usually three times the amount you need to keep it running. Surge wattage is the most power you can get from your generator. Now that you understand how wattage works, you can figure out how to choose the best generator size for your needs.
Safety Tip: Protect your generator and your home with a circuit breaker. If a generator is not using a circuit breaker, it will eventually overload and overheat. If the generator is not shut off once overheated, it could catch fire.
Mathematics of Calculating Generator Sizing
The owner's manuals for most generators include examples of what kinds of structures and devices they can provide power for. However, here is an example of calculating generator sizing yourself.
For example, assume you want a generator that will power a small refrigerator. You consult the refrigerator owner’s manual and find that the running wattage for the device is 350 watts.
- Running Wattage (R) = 350 watts
- Starting Wattage (S) = 350 x 3 = 1,050 watts
- Total Wattage (R + S) = 350 + 1,050 = 1400 watts
The total wattage you need to run a small refrigerator would be 1400 watts, so you would need a generator that provided at least that many watts.
Tip: For best results, always use a generator that can comfortably handle all your power needs while using no more than 90 percent of its capacity.
Types of Generators
Generators come in several different wattage sizes. Although there are solar generators and battery generators, most are gas generators, using propane, natural gas and diesel fuels. There are basically three kinds of generators to choose from.
Portable generators are powerful enough to provide electricity for outdoor activities such as camping, tailgating and other events. They’re easy to take just about anywhere and relatively affordable. They can also provide emergency power in the event of a blackout or storm.
Inverter generators provide electricity but with less noise and more fuel efficiency than other generators. Inverters also convert their AC power to DC power, making them ideal for RVs and battery-operated devices.
Whole house generators provide a backup for your home’s power needs in case of a blackout or storm. They are hardwired to your home. They can quickly provide the power your home needs in case of an interruption to your regular power grid, whether through automatic generator transfer switches or manual generator transfer switches.
Safety Tip: Never use any generator inside your garage, home or other structure, even with the windows or doors open. Carbon monoxide is extremely dangerous and virtually undetectable.
With a little math and a look at what you need to keep your life running, you can easily answer the question “what size generator do I need?” The best thing is to make sure you have an answer before an emergency demands one.
When it comes to choosing the right size generator, determine the usage and wattage your lifestyle or project will require. Ready to find the generator you need? We have options to deliver online orders when and where you need them. You can also rent a generator from your local Home Depot.