A home generator can help keep things operating a little more normally, even when the power goes out. That leads to a common question: What size generator do I need?
There is a wide range of different generator sizes and what your generator can do. You don’t need the same kind of generator if you’re just looking to keep the lights on versus running several appliances for hours.
We discuss how you decide how much power you need in your generator, and what size of generator you need to meet that kind of demand. In addition, you’ll learn basic safety precautions to make sure your new generator works the way you want it to.
Table of Contents
What Size Generator Do I Need?
The answer to this question depends a lot on the size of the house and how many appliances you want to run in the house.
An average size home being conservative would need 5,000 – 7,000 watts on average.
There’s a big difference between the power demands of a few lights, a refrigerator, and a laptop, and the power demands of a full A/C unit, large freezer, and water heater.
The things you need to ask yourself are simple. What do you want to run with your generator? What kinds of appliances must run, which are more optional, and which will you give up entirely during a power outage?
Having that list is critical for understanding how much capacity you need in your new generator. Some things to consider:
- Charge cell phones
- Refrigerator, freezer, backup freezer
- A/C, fans
- Home heater, space heater
- Sump pump
- Water heater
- Power for medical equipment, CPAP machine, etc.
- Dishwasher, microwave
- Washing machine, dryer
- Blender, toaster, coffee maker
- Computers, gaming computer or console
The difference between asking “How big of a generator do I need to run a house?’” and “How big a generator do I need?” usually comes down to how much of your house you need to power with that generator.
Difference Between Watts and Volts and Amps
Keep that appliance list in mind as we talk about how we measure power, and how those measurements can make a difference in the sort of generator you need.
Generators all measure their output in even when the power goes out. Volts measure how strongly an electrical current can be carried through the system, while Amps (Amperes) is a measurement of how much power your appliances and personal electronics need.
There’s a relatively simple formula for calculating amps into watts, and you’ll need to use that formula to decide how large a generator you need.
Formula: Wattage = Amperes x Volts.
In the USA, most standard outlets run on 120V. Anything that can plug into and run on a standard outlet uses that voltage.
However, the USA also has a second standard voltage, 220V, for some higher-power appliances. Many of your major kitchen appliances might use 220V, while smaller appliances like your TV and alarm clock will use 120V.
Calculating How Many Watts You Need
The next step is to look at the list of appliances you need, want, and can do without from before.
You should be able to find the amps and voltage of each appliance in the need and want categories.
Ignore the last category for now, but you may want to come back to it later and see if you can use one or two of those appliances after all.
It should be fairly simple to find electrical information. Most appliances will have a small panel with the model number and other relevant information printed on the back.
If you can’t find that information or it’s faded, try looking up a user’s manual for each appliance in your records or online.
Add the wattage for all of your appliances together. This is a good starting number but is likely a little higher than you actually need for your generator.
After all, it’s rare that you’ll need all of your appliances running at once. Think about how often you use these appliances all together at the same time.
If you don’t often run the dishwasher and washing machine simultaneously, you probably only need to account for the wattage of the higher use appliance to determine how big your generator needs to be.
Once you have a list of the appliances you need and a good estimate of the highest watt use, estimate 100 or so watts higher.
That is a more accurate number, but there are still a few things you need to consider before picking your generator.
Starting Watts vs. Running Watts
You’re close to the wattage your generator needs, but there’s one more thing you need to take into account first.
Many appliances and even smaller electronic devices have a surge in demand when they first start, and then a slightly lower running wattage.
The running demand is what these appliances list on their specs, but you’ll also have to look up the starting surge to make sure you have a generator that can handle the initial demand.
If the power goes out, your generator will probably deal with a starting surge from almost all of your appliances that are always on. Your refrigerator, freezer, and water heater at a minimum.
If you have a separate freezer or are running the A/C or central heating when the power goes out, you’ll also need to account for those.
Your dishwasher, microwave, and other appliances likely won’t be running all at once when the power goes out.
One or two might be, so you should give yourself some wattage in case those appliances are running, but you don’t need too much.
If you’re trying to run all of your appliances off a generator, try giving yourself 1,000 to 2,000 additional watts to cover starting surge.
Why Is Getting the Right Size Generator Important?
By this point, you might already have an answer to what size generator do I need but still wondering if you can cut a few corners on your generator to save a little money.
The truth is you can, but not by under-powering your generator for the appliances you want to run.
The best way to reduce the size of the generator you need is to reduce the electrical burden on your generator by using fewer electronics during a power outage.
Otherwise, you absolutely need to make sure you have a generator that can handle the highest likely capacity your home will need during an outage.
We say highest likely because the highest likely draw is usually a good bit smaller than the highest possible draw.
If your generator cannot handle the amount of electricity you ask it to produce, one of two things will happen.
A modern generator will shut off instead of trying to produce more electricity than it can.
Otherwise, the generator will try to meet demand, and will likely overheat in the process. Eventually, it will shut down, but not immediately.
Either option is likely to cause damage to your appliances and personal electronics.
It might not show right away, or you might need to replace an appliance the very first time your generator fails to meet demand.
Benefits of the Right Size Generator
Knowing what size generator is needed to power a house has a lot of benefits. It’s not just about avoiding the consequences of a too-small generator.
Picking the right generator for you and your home will give you these benefits and help your generator last longer. Not to mention making power outages more comfortable.
1. Avoids Random Failures
A generator operating at or over capacity will sometimes fail, even if it doesn’t truly overheat. The more stressed the generator is, the more likely it is to have these random failures.
Sometimes the solution is as simple as turning it back on. However, these failures can also be a sign that you need to repair something.
Frequent random failures can also be a sign that you need to replace your generator soon. This is often the case if you’ve used it extensively for several years.
2. Longer Lifespan
If you aren’t stressing your generator every time you use it, it will also last longer.
Some less expensive recreational generators might not be that expensive to replace. However, the models designed to run your home tend to be more expensive.
Avoiding costly replacements can help you get more out of your investment.
Avoiding short circuits, unexpected loss of power or damage to your appliances can also be a safety concern. This is especially true in the cold of winter and the heat of summer.
Making sure you have a generator that can keep your home comfortable helps make sure you’re never without power when you need it.
It also helps avoid heatstroke, fires, and other possible complications that come with a faulty or under-powered generator. If you have a basement with a sump pump, consider how you may need to power it so you don’t have flooding.
Do Large Portable Generators Work Like Home Generators?
Not quite. The biggest difference between a home waiting generator and a portable generator is that the former has lower Total Harmonic Distortion (THD).
Meaning, it cannot be above 3% if you want to run smaller and more delicate appliances.
Laptops, TVs, and most electronics that are not counted as appliances count among those more delicate appliances.
These generators can also have different fuel sources, with portable generators using gas or propane, while stationary generators often use natural gas.
They have lower TDH, but they do have a lower overall power capacity. You won’t be able to run your whole home on a single inverter generator.
However, many have a parallel capacity that allows you to run two generators simultaneously.
No matter what types of generator you use, you also need a transfer switch to protect your appliances and electronics.
You’ll also want to get professional installation for both the generator and the transfer switch.
Some electricians will also handle any additional permitting required by your municipality and HOA, but not all.
You should make sure you have all the required permits before buying a new generator.
Two of the Best Generators You Can Get
Getting the answer to how big of a generator do I need to run a house isn’t enough. That is because it can be a lot of work to find the right generator for your home.
Thus, here are two of the better options for many people. They aren’t whole house generators. However, while these generators might not be quite the right capacity for your home, both generators are from good and reliable companies whose models you can trust.
This more extensive guide can also help you find the right generator for a wider range of applications.
1. Westinghouse EGen 9500 DF
This unit is a fairly standard gasoline-powered generator designed to work with your home, or alternatively, as a portable generator for your camper or a mobile camping appliance.
It offers up to 12 hours of runtime, with a 6.6-gallon gasoline tank. Its fuel gauge makes it easy to tell when your generator needs a refill and helps make sure you don’t go without power overnight.
It’s transfer switch ready, which will make it easier for an electrician to install the generator in your home.
It’s also designed to be more long-lasting, with a three-year limited warranty, automatic low-oil shut down, and a cast iron sleeve.
With gasoline, you get 9500 Running Watts and 12500 Peak Watts operational capacity.
Alternatively, you can operate the generator with propane for slightly higher power capacity.
That’s about average for what most American homes need, making this an excellent choice for anyone looking primarily to keep their major appliances running through outages.
2. Champion Dual Fuel RV Ready Portable Inverter Generator with Electric Start
The Champion 3400-Watt Dual Fuel RV Ready Portable Inverter Generator is an inverter generator runs on either gasoline or propane, whichever is more convenient or provides the level of power you need.
However, it’s a little less powerful than a non-inverter generator, maxing out at about 3400 watts running power. It has an electric start.
It also has a battery, allowing you to store a little power as you go and helping if the generator shuts off a little earlier than you’d prefer.
This generator is a little smaller. You will find it appropriate for camping and tailgating more than truly powering your home, but in those capacities, it works well.
It also offers quieter operation, which helps anytime there isn’t a wall between you and the generator while it’s running.
This generator also has a three-year warranty, with unlimited lifetime customer support.
What Size Generator Is Needed to Power a House
Having a home generator can be an essential part of your emergency plan for when the power goes out.
It’s even more important if you live somewhere with regular power outages or weather emergencies. Also, generators are important if you have medical equipment, critical appliances, and livestock to consider.
Just having a generator isn’t enough, though. You also need to have a generator big enough to handle the demands of your appliances and home.
That takes a little math, but we’ve shown you how to figure out how big your home generator needs to be.
Consider carefully whether a portable generator can meet your needs or need a more permanent solution by adding a whole house generator. There are many types in between these as well.
Remember you also need a transfer switch for generators to ensure the connection is stable, safe, and efficient.