What Size Generator for My House Do I Need? How to Size a House Generator Properly

Share This Post

So you’ve decided you’re going to invest in the peace of mind that only a backup generator can offer – great choice. You’ll sleep soundly knowing you’ve done everything in your power to keep your home or business protected during that next power outage. While neighbors are scrambling to save the food in their fridges or heat their homes, you and your family won’t skip a beat.

However, the big question now is – what size generator for my house is best? And unfortunately, sizing a home generator is a bit more complicated than you may think. It depends on the size of your home, of course, but also what specific appliances you want to have access to when the utility power goes down. 

However, you don’t have to stress over how to size a house generator any longer. We’re here to help. As the #1 generator company near Barnstable, Bristol, Middlesex, Norfolk, & Plymouth counties, you can trust that you’re in good hands by following our advice below. Before we explain how to size a whole house generator, let’s talk about the importance of proper sizing.

The Importance of Sizing a Home Generator Correctly (and Why it’s so Hard to Estimate Generator Size) 

It’s no secret that sizing a home generator is of the utmost importance. It can be the difference between living your life with no interruptions when a power outage occurs, or kicking yourself for sizing too small when you realize you don’t have the ability to power everything you need.

But, chances are, you’ve quickly realized it’s not as easy to estimate generator size requirements as you initially thought. That’s because each and every situation is unique.

We likely don’t have to tell you that home generators come in different sizes – from as small as 8.5kW to as large as 20kW. The obvious assumption is that your generator should be sized according to your square footage. Smaller homes need a smaller unit, and vice versa…right?

Not quite.

While the size of your home will dictate your generator size to some extent, it’s actually more important to consider the appliances you’ll use in the event of an outage. Here’s why: if you fail to size your unit large enough, you won’t have access to the appliances you need most! Similarly, if you size your unit too large, you’ll end up paying more than necessary on the initial investment and running the generator over time.

There is a sweet spot to be found – and below, we’ll help you pinpoint it accurately. So – without any further ado, here is how to size a house generator. 

How to Size a House Generator: Tips for Accurate Whole Home Generator Sizing

How to Size a House Generator

Before we simply come out and answer your question – what size generator for my house is best? – we want to teach you the basic steps for how to size a house generator. This will help you more accurately estimate generator size requirements for your unique situation.

With that said – our recommendation is always to reach out to a professional like Premier Generator. Our team can help you weigh the various factors at play and do a walkthrough of your property. This inevitability leads to more accurate estimations. However, here are the basic factors to keep in mind for whole-home generator sizing.  

What Appliances Do You Want to Run During an Outage?

As mentioned earlier, the first step in how to size a whole house generator is considering exactly which appliances you need access to in the event of an outage. This varies from household to household – but there are a few essentials everyone wants access to.

For example, you’ll definitely want to be able to keep your refrigerator and freezer on to save all your food from spoiling. You’ll also want to keep the lights on, and you’ll likely want the option to use your air conditioning unit or furnace. This is pretty universal across most homes.

Now – at this point, you should consider essentials that are specific to your home. Maybe you have medical equipment you need access to, like a CPAP machine. Maybe you want access to your computer, sound system, and other equipment.

You can also take the opposite approach here, starting with which appliances you don’t need during an outage. Maybe you can live without the TV for a few days – or your ice maker. Maybe you don’t need access to that mini fridge in the entertainment room. 

Really, this is something only you can answer for yourself – but one thing you should avoid is associating the size of the appliance/equipment with energy needs. It may surprise you to learn a hair dryer can use 1200-1875 watts of electricity! Meanwhile, an energy-saving LED bulb uses as little as 6 watts of electricity. 

Base Your Estimates on Start-Up Wattage – Not Running Wattage!

During our walkthrough at your property, we can help you weigh the options and figure out everything you do or don’t need access to in the event of an outage. We’ll also be able to calculate our estimations accurately based on start-up requirements – not running requirements. 

This is a common mistake that homeowners make when it comes to whole-home generator sizing on their own. Your generator doesn’t just need to be capable of running your appliances – it needs to be capable of starting them all up. The demands for starting up appliances are higher than running the unit. This is best illustrated with an example.

Most appliances state the running wattage right on the appliance itself. For your refrigerator or freezer, that can be as high as 700 running watts. Now – to get the startup wattage, you’d multiply that figure by 3x. So, to start up that one appliance you need to account for up to 2,100 watts!

This is why we always recommend getting professional help – as it’s these little intricacies that make accurate whole-home generator sizing so difficult. With that said, let’s talk about the other factor at play – your home’s square footage.  

Factor in Your Home’s Square Footage When Sizing a Home Generator

The reason your home’s square footage is so important for whole-home generator sizing is that it dictates the electrical needs of certain appliances like air conditioning or heating. It also influences lighting requirements or the sump pump on your property. 

If you’re just starting out this journey of buying a home generator, factoring the size of your home’s square footage is a great way to get a base estimate. But, as mentioned above, doing a walkthrough of your property to discover which appliances are essential is your best bet.

When in Doubt, Should You Size Up or Down for Your Whole Home Generator?

If you’re following along with the advice we’ve offered above, you should have a closer idea of what size generator for your house is best. But maybe you’re not entirely confident that the figure you’ve landed on is accurate. Or, maybe you’re specific needs are between sizes. 

As a result, you’re probably wondering if it makes more sense to size up and have more power than needed, or size down and maybe cut back on your appliance needs. Sizing down means you save money on the initial purchase price and the use over time. On the other hand, sizing up gives you the peace of mind that has you interested in a whole home generator in the first place. That’s why we recommend sizing up.

You want to keep your generator running comfortably. That means you should size up slightly to ensure it’s never working beyond 90% capacity. If that does happen, the risk of overheating rises – which leads to an increased risk of Kohler generator repairs being needed.

We may sound like a broken record here…but reach out to us to help with this element of purchasing a home generator. You don’t have to size the equipment on your own! 

So, What Size Generator for My House is Ideal?

sizing a home generator

So, what size generator my house is recommended? By now you should have jotted down a list of the total wattage you need your generator to be capable of supplying. Here are some basic estimations based on different home sizes running the most essential appliances:

  • 1,000-1,500 sq. ft.: 6 kW – 8.5 kW Residential Generator
  • 1,500-2,000 sq. ft.: 8.5 kW – 10 kW Residential Generator
  • 2,000-2,500 sq. ft.: 10 kW – 14 kW Residential Generator
  • 2,500-3,000+ sq. ft.: 18.5 kW Residential Generator or a Larger Commercial Generator

Remember – these estimations won’t be specific to your home or appliance needs. So get in touch with a generator contractor near you today for a more accurate answer. Or, if you want to learn more about choosing a generator for your home, keep reading – we’ll discuss a few other key factors.  

Other Factors to Consider Along This Journey Besides How to Size a House Generator

Now that you know how to size a house generator you should feel confident in taking the next steps to get the job done. With that said, size isn’t everything – despite what you may have been told! You should also consider the following factors along this journey:

Fuel Source

There are three fuel sources for home generators, but you’ll see two specific fuel sources more than the third. The most common are liquid propane (LP) or natural gas (NG). while diesel generators do exist, they have their drawbacks – and as a result, the former two options are your best bet.

Each comes with its own pros and cons. Liquid propane generators are more eco-friendly with a quieter operation. Just know that you’ll have to have a propane tank installed on your property as well to fuel the generator – and with this tank comes a finite amount of power. 

That’s the beauty of a natural gas generator. Because you’re hooked up directly to your city’s natural gas lines, you have access to all the power you need. With that said, it’s not uncommon for natural gas to be knocked out at the same time as utility power – so these are seen as less reliable than their liquid propane counterparts. 


There are quite a few generator brands on the market – but we only deal in Kohler whole house generator installation. There’s a reason for that. A common question we get asked is…how long do whole house generators last? With a Kohler generator, you can expect to get decades of reliable use from your investment. They far outlast the competition and are seen as more reliable. 

When it comes to investing in a home generator the goal is peace of mind – and nothing can offer that quite like a Kohler!


If you haven’t considered how you’ll get your new unit installed, understand that this is just as important as the specific generator itself. A quality installation allows you to get the most out of your unit in terms of longevity and unlocks peak reliability. On the other hand, cutting corners on installation leads to costly repairs down the road and a lessened lifespan. 

Neither of these is an acceptable outcome – which is why going with only the best generator contractor in your area is of the utmost importance! 

Other Features

If you haven’t fully dived into the world of whole-house generators, you’ll be amazed to see some of the features you can get these days. From remote monitoring through WiFi to an extended warranty, you should weigh all the options on the market to make sure you’re getting the most bang for your buck. For more information, read our full guide on how to choose a home backup generator. Or, get in touch with us today…

Want Help Sizing a Home Generator Correctly?

If you’re in southeastern Massachusetts, you can count on Premier Generators to not only help you size your unit – but help you install and maintain it over the course of time. We’re known as the most trusted choice for anyone seeking a whole-house generator installation company near the following counties:

  • Barnstable
  • Bristol
  • Middlesex
  • Norfolk
  • Plymouth

You get the most dependable system possible since we only deal in Kohler. And through our sophisticated installation process, you’re getting a job done right the first time around. We never cut corners – as that would compromise the main reason you’re investing in a generator: peace of mind.

The best part? Through our service and maintenance plan, you get an incredible 10-year warranty protecting your investment over the next decade. And if your business needs protection too, reach out about our commercial generator installation!

Closing Thoughts on How to Size a Whole House Generator for Your Home

There you have it – everything you need to know about how to size a whole house generator for your home. We hope you gained the answers you were seeking for questions like – what size standby generator do I need for my house?

As you can see, whole-home generator sizing is not a one-size-fits-all process – but you should feel more confident in your next steps at this point. 

Are you still wondering what size home generator do I need? Reach out to Premier Generators today and we’ll schedule our walkthrough at your property. You’re just a few clicks away from getting the peace of mind you’ve been searching for!