When purchasing backup power, deciding what size generator you need to power your house during a power outage is an important consideration. The size of the generator will determine how many appliances and electronics you can run at the same time. Follow this guide to determine the right size generator for your home’s needs.
Calculate Your Power Requirements
The first step is calculating your home’s running wattage requirements. Make a list of essential appliances and devices you want to be able to run during an outage. For each one, determine the startup and running wattage typically listed on the device nameplate.
Add up the running wattage for all devices that could potentially be on at the same time. This is the minimum wattage your generator will need to handle. Remember to include major appliances like refrigerators, freezers, furnaces, and water heaters, which cycle on and off.
Allow for about 30% more capacity as a safety factor for motor startup loads. This ensures the generator won’t become overloaded when multiple devices turn on simultaneously.
Consider Your Fuel Source
Once you know the wattage you need, the next decision is which type of fuel to use – gasoline, diesel, propane, or natural gas. Smaller portable generators, up to about 10,000 watts, typically use gasoline. Larger standby whole home units run on diesel, natural gas, or propane.
Gasoline and diesel offer more portability and independence since the fuel is self-contained. However, refueling requires periodic trips to the gas station, which may be impossible during long outages. Propane and natural gas generators integrate into your existing household fuel supply lines, meaning you don’t have to refill fuel tanks manually.
Choose Between Portable and Standby Generators
Portable generators range in size from about 1,000 to 5,000 watts. They can be moved in and out of storage as needed and transported for use in other locations. Home standby generators permanently mount outside and connect to your existing electrical panel and fuel line. Sizes range from about 10,000 to 150,000 watts for very large homes.
Consider a standby whole home generator if you want backup power for your entire home without having to plug in appliances individually. Standby generators also have auto-start features. This means your house will only be without power for a minute or two. Get a portable if you only need to run a few essential devices.
Allow for Startup Wattage
When sizing your generator, be sure to account for startup wattage. Appliances require momentary bursts of extra power for starting motors, compressors, and pumps, which exceeds their continuous running wattage.
For example, a 5,000 watt generator can handle a 4,000 watt load. But during startup, that load may temporarily spike to 6,000 watts, which can overload the generator. Size your generator 30% higher than your total running wattage to allow for startups.
Calculate Your Total Running Wattage
Add up the maximum wattages of all essential devices that could realistically run simultaneously during an outage. This determines the minimum generator size needed. Here are some typical wattages for common household devices:
- Refrigerator – 700 watts
- Furnace fan – 800 watts
- Sump pump – 800 watts
- Microwave – 1000 watts
- Window AC – 1500 watts
- Clothes washer – 500 watts
- LED lights – 10 watts each
- TV and electronics – 100 to 400 watts
Don’t forget essentials like phone chargers, internet modems, coffee makers, and computers. Make a master list of all devices you want to be powered.
Consider Future Load Increases
When choosing your generator, think about potential load increases down the road. You may end up adding larger appliances or more electronic devices over time.
Spending a little more now for extra capacity leaves room for expansion later. Otherwise, you risk overloading a generator that was properly sized at the time of purchase.
Choose the Right Type of Generator
- Portable generators – Best for small backup loads up to about 5,000 watts. Easy to move and store. Run on gasoline.
- Inverter generators – Portable generators that produce clean, stable power for sensitive electronics. More fuel efficient and quieter.
- Standby whole home generators – Permanently installed units that power your entire electrical system. Connected to natural gas/propane lines or large exterior fuel tanks. Sizes from 10,000 to 150,000 watts. Provide automatic backup power to the whole home.
- RV generators – For use in RVs. Very compact and portable. Have RV-plug outlets built in. Not ideal for home use.
Allow for Voltage Drop
Voltage drop happens when electrical current passes through wires. It increases with higher wattages and longer wire runs from the generator to the devices. After a certain distance, a voltage drop can cause appliances to perform poorly or not start up.
When sizing your generator, factor in about 10% extra capacity to account for voltage drop if your generator will be located far from the devices it powers. A soft start feature also helps reduce voltage drop during motor startup.
Get Help Choosing What Size Generator You Need
Determining your home’s generator requirements can get complicated with multiple appliances, motor loads, and expanded future needs. Consult with a generator expert for help choosing the right size unit and have it professionally installed. This ensures your generator is adequately sized, installed properly, and ready to provide automatic backup power when you need it.
In summary, calculating your generator size involves:
- Making a list of essential devices and their wattages
- Totaling the running and starting wattages
- Choosing a fuel type – gasoline, natural gas, etc
- Allowing for future expansion
- Picking between portable and whole home standby units
- Considering voltage drop over long wire runs
- Getting professional help choosing and installing the right system
Take the time to size your generator properly. This ensures you get clean, uninterrupted backup power to run your home’s essentials when you need it most.