What Size Home Generator Do I Need? Find Out in 5 Simple Steps

Champion home standby generator installed in front of a rural cabin at night.

Goldilocks had to choose from three beds: too big, too small, and just right. 

Homeowners buying a generator face the same decision, but more so. 

While Goldilocks could have rested just fine in a too-big or too-small bed, neither was going to cost her more to run (a too-big generator) or make her lose electricity just when she needed it most (a too-small generator.) 

That’s why properly sizing your generator is so important. A too-large generator makes you spend an unnecessary amount both to purchase and to run, but a too-small generator is even worse. If your household puts too much demand on a generator at one time, the generator is in danger of overloading — a process that can shut off your immediate power and ultimately shorten the generator’s lifespan. 

Fortunately, a free, no-pressure generator installation quote can easily help you avoid the inconveniences of a too-small generator. When most installers recommend a generator size for your home, they’ll round up your household’s power needs so that you’re never surprised with cold water in the middle of a shower. 

In fact, we at Duthie specialize in carefully sizing home generators so you’ll enjoy a generator that will easily power all your household’s needs, but not require more upfront and running costs than you actually need to pay. 

Still, it’s always best to be an informed consumer so you can discuss size knowledgeably with your installer. Then you’ll know the process that goes behind the recommended size and gain a deeper understanding of your household’s power needs. 

So here’s a simple 5-step guide to discovering your just-right generator size:


1. How Big is My Home?

Your home’s square footage is an effortless rough estimate of your perfect standby generator size: 

Up to 1,500 sq. ft. with 3-ton AC: 8.5 kW

1,500 – 3,000 sq. ft. with 4-ton AC: 12.5 kW

3,000 – 4,000 sq. ft. with 5-ton AC: 14 kW

But every household and family’s power needs are different, so it’s best to double check this rough estimate. 

So on to Step 2:


2. What Do I Want My Generator to Power? 

Some families don’t want to notice the power’s out. These households can often afford to buy generators that will keep everything running just the way it usually does, blackout or no blackout. 

If you’re one of these families, you can estimate your generator size in two ways: 

  1. Obtain a year’s worth of electric bills and find the highest monthly wattage used in the home. 
  2. Look at your electric bill to see your peak load wattage. 

However, these generators (often 20kW or above) often cost more than $5,000 and require more fuel than smaller generators. 

So most households prefer to save on costs by powering only essentials and a few nice-to-have electronics. This gives them comfort and convenience without extra bills to pay.

Essentials usually include: 

  • Central A/C
  • Main lighting circuits
  • Fridge + freezer
  • Microwave
  • 1 laptop per family member
  • Garage Door
  • Washing Machine
  • Sump Pump (if your home needs one)

You can often throw in a few nice-to-have electronics too; for example, an average TV only needs 190 watts to run. 

Pro Tip

Electric Stovetops are not essential if you have a microwave, though they are nice to have. Just remember that they need roughly twice the wattage a microwave needs. (2,100 volts vs. 1,300)


3. How Much Power Do They Need To Start? 

Now that you have your list of chosen appliances, find out how much power (in watts) your chosen electronics need to start running. This is called “surge wattage,” and it’s important because most appliances demand much more power to start up than to run.

You can find your appliances’ surge wattage in several ways. 

  1. For an estimate, use this list from Energy Today. It includes both starting and running wattage, so remember to always use the starting wattage:

(Energy Today) 

  1. For your exact appliances, check their manufacturing labels. They will contain surge wattage as well. 
  2. You can also search an appliance’s make and model online. When looking it up, include the words “surge wattage.”

Once you have your chosen appliances’ wattages, add them to find the upper limit of how much electricity your current household may need at any given time. 


4. Add 15-25% 

Now that you have your upper power need limit, add 15-25%. 


As said before, you don’t want to overload your generator; overload not only cuts off your power and shortens the generator’s lifespan, but can also damage connected electronics. 

So to avoid any chance of overload, size up your estimated power needs from Step 3 by 15-25%. 

This not only prevents you from being caught short, but also allows you to power future electronics (such as a larger refrigerator or new medical device) in addition to your present appliance list. 


5. Choose a High-Efficiency Generator (And Round Up!)

If your desired wattage falls between two sizes (for example, 10,780 kW) round up to the nearest generator size, not down. That way, your family will be able to live in reliable comfort with no fear of overload. 

Now that you have your final wattage number, make sure you find a high-efficiency generator. A high-efficiency model ensures that you can power your home without paying for unnecessary wattage or fuel. 

For our customers, we found Champion standby generators to give the best value, including fuel efficiency. They come in the three sizes mentioned in Step 1 — 8.5 kW, 12.5 kW, and 14 kW — so that homeowners can find the perfect size for their house and individual family needs. 

Goldilocks would be proud.  

Interested in installing a standby home generator? Get a free, no-pressure quote from our experienced standby generator team at 866-838-7962 or info@duthiepower.com We look forward to helping you find and install the perfect generator! 

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