What Size Generator Do I Need?

As natural disasters and storms become more prevalent across America, homeowners are deciding to purchase a generator to power their homes when local power fails. The big question is, “What size generator do I need?”

Many people with recreational vehicles also choose to add generators for backup power in campgrounds or on primitive campsites. Generators are popular for contractors working on sites without electricity, too.

How to Choose a Generator Size

There are many considerations when deciding on a generator for your home. The foremost should be its wattage output and if it can power the necessary elements in your home.

Understanding the wattage needs is vital in deciding the size generator for your home or RV. A generator is rated based on the watts needed to start an appliance, run the device, or operate through a surge of multiple devices that start simultaneously. The surge is the maximum the generator can produce. Starting a device requires more watts, which reduces the running rate after beginning. It is best to turn items on one at a time to reduce the risk of damage to the generator.

Home use generators come in different styles, including standby and portable styles. Standby generators are permanently installed outside the home [or business] and, via a sensor, start and run automatically when other power ceases. Standby generators can power the whole house.

Move portable generators to run as needed or placed them in a shelter for semi-permanent use. Portable generators come in a range of wattages, styles, and types. The smallest wattage generators can power electric needs with minimal power draw, while the larger units can power HVAC, refrigerators, lights, and appliances.

Will you be running an extension cord from the portable generator to power a few appliances, or will you install a transfer switch and outside receptacle in your home? Installing a transfer switch is the safest option.

Most home standby generators operate by natural gas, propane, diesel, and newer models can run on solar power. Portable generators operate on gas, propane, diesel, or solar, and some new generators run on hydrogen. Since they are new to the market, the current price is high. How you want to fuel your generator will be another consideration.

Choosing the Right Size Generator

Make a list of the appliances in your home that you will want to power via a generator to determine the wattage requirements. Consider your family’s necessities [to be comfortable] during an extended power outage.

Household Appliance Wattage Requirements

ApplianceWattage Needed
Central air conditioning2,000–4,000 watts
Window air conditioning unit600–1,500 watts
Electric furnace5,000–25,000 watts
Water heater3,000–4,500 watts
Sump pump1,500 watts
Radiant heater1,300 watts
Outdoor lighting500–1,000 watts
Coffee maker400–800 watts
Microwave1,200 watts
Refrigerator/freezer600–800 watts
Space heater1,250 watts
Toaster1,100–1,700 watts
Electric oven5,000 watts
Personal computer500–2,000 watts
Television100–350 watts
Table lamp150 watts
Hair dryer1,200–1,500 watts
Cell phone battery charger10 watts
Video game console200 watts
Washing machine750 watts

If you want everything in your home powered during an outage, then you should consider installing a home standby generator. A portable generator may best fit your needs if you only need a few appliances or comfort items, although you can buy one up to 15,000 watts.

2 Types of Generator Options

  1.  Standby generator – A standby generator will be the highest-priced option, but once installed, it will provide the least hands-on work for you. As a permanent feature outside your home, it provides security by turning on automatically during a power outage. Standby units run on natural gas, propane, diesel, and solar.
  2. Portable generator – Portable generators are compact and relatively easy to carry or roll around.  The range in weight is from a few pounds to under 200 pounds. Fuel sources are mainly gasoline, propane, or solar energy. Gas is available from a gas station, and propane can be found at a gas station and most home improvement-type stores, while solar energy comes directly from the sun. Some portable generators come in a dual-fuel model that can run on either gas or propane.

A portable generator can be stored in your garage or shed until it is needed. Many homeowners choose to install a small shed for the generator close to the home or business and adapt the shelter with exhaust and power cords. See Portable Generator Shelter for more information.

  • (Portable) Inverter generator – Inverter generators differ in the way that they produce electricity. Inverter generators deliver electricity in three phases, creating a high-frequency alternating current (AC), which is then inverted to a direct current (DC) and finally inverted once more to a stable AC output. It creates a more reliable current flow for sensitive items like mobile devices and cell phones. An inverter generator may have options for gas, propane, or dual-fuel.
  • (Portable) Gasoline generator – The most common fuel for portable and inverter generators is gasoline. Gas is an easily obtained fuel and can be purchased and transported in approved containers. Generator fuel tanks vary by size, and you will need to monitor how long the generator runs before needing to refill the tank. For safety, allow the engine to cool – never refuel a tank with the generator running.
  • (Portable) Propane generator – Many generators have the option to run on propane. Some are dual-fuel, offering both gas and propane choices. Propane burns cleaner and therefore has fewer emissions. Unlike gasoline or diesel, which degrade over time, propane does not deteriorate. Operating the generator on propane reduces slightly the number of watts produced compared to gasoline.
  • Diesel generator – Most diesel-operated engines are in standby generators, though there are some portable diesel generators. Diesel engines provide a more efficient power output than gasoline, and there can be cost benefits to buying a diesel generator. Diesel and gasoline may deteriorate in about a year, and fuel prices are a consideration for long periods of operation.
  • Natural gas generator – Generators fueled by natural gas will be among the standby generator brands. Some portable generators may be adapted to run on natural gas. Like propane-fueled generators, natural gas generators produce a significantly lower emissions rate, making them an excellent choice for whole-home backup power.

However, natural gas does not operate well in frigid climates, so if you live in Canada or states bordering Canada, check with the generator provider about recommended fuel options.

  • Solar generator – Solar power is becoming a popular option for those wanting to “live off the grid.” The initial cost to install a whole-home solar generator is expensive, although, over time, it saves on fuel because it is renewable and free. Portable solar generators are ideal for camping or keeping in the car as an emergency source of electricity.

The consideration for using solar generators is living in a sunny region, as it creates no power without sunlight. Smaller solar generators do not produce much energy and are generally limited to smaller appliances or lights.

What Causes a Power Outage?

Power outages can result from storms, downed lines, or a failure of the power grid. Blackouts can happen when the national power grid becomes overwhelmed, as in 2003 when heavy use during a heat wave caused our system in the northeast and mid-central states to crash.

Aging infrastructure is another cause of power loss. Older transformers can blow out, poles carrying lines can deteriorate, and the power needs of consumers can overwhelm the local provider’s ability to provide sufficient electricity to meet the requirements. Power outages can be local or regional, and it may take days for crews to restore power.

While it may be a fun experience to live by candlelight for a few hours, we have become creatures of comfort. We want our HVAC systems to work and our food to remain unspoiled. Having running water – powered by electric pumps – and working toilets are essential for our comfort. Medical conditions also need electricity-powered equipment, so you want to prevent life-threatening issues.

Conclusion

You now have an overview of the generators from which to choose. The first step is to decide the wattage needed so you will know the size, then choose between a home standby or portable generator. The brands, models, and types are the next consideration. Once you have chosen a brand, select the model and type of fuel option. Order online or shop at your local home improvement center.

what size generator do i need

FAQ

How do I know what size generator to buy?

You will need to do some homework, but once you know the devices and appliances you need to run, you can add the watts required. Every generator is designed for the number of watts it can produce. You should choose a generator rated at least 1000 to 1500 watts higher than the total watts you have calculated, and this amount covers a potential surge to the generator.

How do I figure out the watts needed for a generator?

There are lists of average wattage draws for devices and appliances that you can use. Most devices and appliances have energy guides (see operator’s manuals or look for energy use stickers). Add the running watts and total to determine the size generator you need. It is best to buy a generator that has at least 1000 to 1500 watts more than you need to allow for potential surges to the generator when starting devices and appliances.

How many watts does it take to run an average-sized home?

If you need to run HVAC in addition to appliances and lights, a 5000 to 7500-watt generator should be sufficient to maintain comfort in an average-sized home. However, it is always best to calculate your home’s energy needs before buying a generator based on a guess.

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