Generac generators are sold in more sizes than any shopper can keep in their head, from a 2,200-watt camping inverter to a 150-kilowatt standby unit for a large building. The brand’s catalog is organized by product family. Most buyers, though, are asking a simpler question: what size do I need, and what will that size actually run?
This guide answers that question with one ladder. Every current Generac size is placed on it, from the smallest to the largest, with the loads each step can carry. You can find your needs on the ladder and read off the model.
You will also learn the two numbers on every generator, how to turn kilowatts into amps, when a portable stops making sense and a standby unit begins, and what pushes you up or down a size. Model figures come from Generac’s own product pages. Appliance wattages are the typical planning values we use across this site. We have not tested these generators.
Generac generators by size
One ladder, from a camping inverter to whole-home power
Model figures are from generac.com, checked October 2026. Appliance figures are typical planning values.
Quick answer
Generac’s sizes fall into four steps. About 2,200 to 3,900 running watts covers a refrigerator, lights and an RV, from quiet inverter models. About 3,600 to 9,500 running watts covers home essentials and well pumps, from GP open-frame portables. From 10 to 28 kW, air-cooled standby units power most or all of a house automatically. Above that, liquid-cooled models run up to 150 kW. Size by running watts, add the largest starting surge, and leave about 20% in reserve.
How we put this guide together
We have not tested these generators. Generac model figures come from the product pages and specification tables on generac.com and from Amazon listings, checked in October 2026. The appliance wattages are typical planning values in line with commonly published charts, and they are the same ones used in our sizing guide and calculator. Your own appliances will differ, so check their nameplates. Generac itself says an authorized dealer is best placed to size a home standby generator.
In this guide
- The Two Numbers on Every Generac Generator
- The Generac Size Chart
- How We Matched Loads to Sizes
- Step 1 on the Ladder: Small Inverters, 2,200 to 3,900 Watts
- Step 2: Open-Frame Portables, 3,600 to 9,500 Watts
- Step 3: Air-Cooled Standby, 10 to 28 kW
- Step 4: Beyond 28 kW
- What Moves You Up or Down a Size
- One Generac at Each Step
- Portable or Standby: Where Is the Line?
- Common Mistakes When Sizing a Generac (and the Fix)
- Pro Tips for Choosing a Size
- Real-Life Scenarios: Find Yourself on the Ladder
- Generac Generators: FAQ
- Your Generac Sizing Checklist
The Two Numbers on Every Generac Generator
Before the chart makes sense, you need two terms.
Running watts is the power a generator can supply all day. You may also see it called rated or continuous watts. This is the number to size on.
Starting watts is a short burst, lasting a few seconds, that helps motors get going. A refrigerator, a pump or an air conditioner needs two to three times its running power for a moment as it starts.
Generac puts the starting figure in many of its product names. The “Generac 10,000 Starting Watt” generator is the GP8000E, which makes 8,000 running watts. Read past the big number.
Watts and kilowatts
Portable generators are rated in watts. Standby generators are rated in kilowatts. One kilowatt is 1,000 watts, so a 22 kW standby unit makes 22,000 watts.
Kilowatts and amps
Electricians think in amps. To turn a generator’s output into amps at 240 volts, divide the watts by 240.
| Generator size | Amps at 240 volts | For comparison |
|---|---|---|
| 5,500 watts | About 23 amps | A 30-amp generator outlet |
| 8,000 watts | About 33 amps | More than one 30-amp outlet can pass, which is 7,200 watts |
| 9,500 watts | About 40 amps | A 50-amp generator outlet |
| 14 kW | About 58 amps | A small standby unit |
| 22 kW | About 92 amps | The most popular whole-home size |
| 28 kW | About 117 amps | The largest air-cooled Generac |
A home with 200-amp service almost never draws 200 amps. That is why a 22 kW generator, at 92 amps, can run a whole house if large appliances are kept from starting together.
The Generac Size Chart
Here is the full ladder. Find the row that matches what you need to run.
| Running watts | Generac model | Type | What it typically runs |
|---|---|---|---|
| 2,200 | GP2500i | Inverter | A refrigerator, lights and chargers, started one at a time |
| 2,500 | GP3300i | Inverter | The same, with more room for a small motor to start |
| 3,000 | iQ3800 Dual Fuel, 3500i | Inverter | A 30-amp RV, or a fridge, furnace fan and lights |
| 3,600 | GP3600 | Open frame | Fridge, furnace blower, sump pump, lights and TV |
| 3,900 | iQ5200 Dual Fuel | Inverter | An RV with air conditioning, or quiet home essentials |
| 5,500 | GP5500E EFI | Open frame | Essentials plus a well pump |
| 6,500 | GP6500 | Open frame | Essentials, well pump and a microwave |
| 7,500 to 8,000 | GP7500E Dual Fuel, GP8000E | Open frame | The above plus a window air conditioner |
| 9,500 | GP9500E Tri Fuel | Open frame | Most essentials through a 50-amp transfer switch |
| 15,500 to 18,000 | GP15500EFI, GP18000EFI | Large open frame | Essentials plus central air, with manual setup |
| 10 kW | 10 kW standby | Air-cooled standby | Essentials, automatically |
| 14 kW | 14 kW standby | Air-cooled standby | Essentials plus one central air conditioner |
| 18 kW | 18 kW standby | Air-cooled standby | Most of a mid-size home |
| 22 to 24 kW | 22 and 24 kW standby | Air-cooled standby | A whole home with one or two air conditioners |
| 26 to 28 kW | 26 and 28 kW standby | Air-cooled standby | A large home with several big loads |
| 22 to 150 kW | Liquid-cooled standby | Liquid-cooled | Very large homes and businesses |
Key insight: the jump that matters most is not from one wattage to the next. It is from manual to automatic. Below 10 kW, someone has to be home to start and refuel the generator. From 10 kW up, a standby unit does it alone.
How We Matched Loads to Sizes
The chart uses the same planning figures as our sizing guide. Here are the common ones.
| Appliance | Running watts | Starting watts |
|---|---|---|
| Refrigerator or freezer | 700 | 2,200 |
| Sump pump, 1/3 hp | 800 | 1,300 |
| Well pump, 1/2 hp | 1,000 | 2,100 |
| Gas furnace blower, 1/2 hp | 800 | 2,350 |
| Lights, several rooms | 300 | 300 |
| Television, router and chargers | 300 | 300 |
| Microwave oven | 1,500 | 1,500 |
| Window air conditioner, 10,000 BTU | 1,200 | 3,600 |
| Central air conditioner, 24,000 BTU | 3,800 | 11,400 |
| Electric water heater | 4,500 | 4,500 |
| Electric clothes dryer | 5,400 | 6,750 |
The method, in four steps
- List what must run at the same time. Not everything you own. Only what has to be on together.
- Add up the running watts.
- Add the largest extra starting load once. Find the appliance with the biggest gap between starting and running watts, and add that gap.
- Add about 20% in reserve to the running total.
Three worked examples
Example 1: winter essentials. Refrigerator 700, furnace blower 800, sump pump 800, lights 300 and electronics 300. That is 2,900 running watts. The furnace blower’s start adds 1,550, giving 4,450 starting watts. With 20% in reserve you want about 3,500 running watts. The GP3600, at 3,600 running and 4,500 starting watts, fits almost exactly.
Example 2: essentials on a well. Add a 1/2 hp well pump at 1,000 watts. Now you need 3,900 running watts and about 5,450 starting watts. With reserve, look for 4,700 running watts or more. The GP5500E, at 5,500 running and 6,875 starting watts, covers it.
Example 3: essentials plus central air. Add a 24,000 BTU central air conditioner to Example 2. Running load becomes 7,700 watts. The air conditioner’s start adds 7,600 watts, so starting demand reaches about 15,300 watts. No mid-size portable can do that. This is where a 14 kW or larger standby generator comes in, or one of the very large GP models.
Central air is the load that changes everything. It is the main reason people move from a portable to a standby unit.
Our Generator Size Calculator runs these sums for your own list, and our guide to what size generator you need explains the method in full.
Step 1 on the Ladder: Small Inverters, 2,200 to 3,900 Watts
These are Generac’s quiet generators. They make clean power for electronics and slow down when the load is light.
| Model | Running / starting watts | Weight | Best for |
|---|---|---|---|
| GP2500i | 2,200 / 2,500 | 48 lb | Camping, tailgating, a refrigerator |
| GP3300i | 2,500 / 3,300 | 61 lb | Camping with a little more margin |
| 3500i | 3,000 running | 109.1 lb | RVs and quiet home use |
| iQ3800 Dual Fuel | 3,000 / 3,800 | 107 lb | 30-amp RVs, with propane as an option |
| iQ5200 Dual Fuel | 3,900 / 5,200 | 111 lb | RVs with air conditioning |
Who should stop here: apartment and condo dwellers with a balcony or patio where a generator can run safely outdoors, RV owners, campers, and homeowners who only want the refrigerator, some lights and the internet.
What you give up: 240-volt power. These are 120-volt machines. They cannot run a well pump, an electric water heater or central air.
Step 2: Open-Frame Portables, 3,600 to 9,500 Watts
This is the home essentials range. Generac’s GP models have steel tube frames, wheels and, from the mid sizes up, a 240-volt outlet for a transfer switch.
| Model | Running / starting watts | Fuel | Weight | Best for |
|---|---|---|---|---|
| GP3600 | 3,600 / 4,500 | Gasoline | 105 lb | Basic essentials |
| GP5500E EFI | 5,500 / 6,875 | Gasoline, fuel injected | 172 lb | Essentials with a well pump |
| GP6500 | 6,500 / 8,125 | Gasoline | 172 lb | Essentials with kitchen loads |
| GP7500E Dual Fuel | 7,500 / 9,400 | Gasoline or propane | 204 lb | Flexible fuel for longer outages |
| GP8000E | 8,000 / 10,000 | Gasoline | 198 lb | Larger homes, 30-amp transfer switch |
| GP9500E Tri Fuel | 9,500 / 12,500 | Gasoline, propane or natural gas | 219 lb | A 50-amp transfer switch |
Who should stop here: homeowners who are usually home during outages, who lose power a few times a year, and who can live without central air for a day or two.
What you give up: convenience. A portable has to be wheeled out, started, refueled and run outdoors, at least 20 feet from the house. It also needs a transfer switch or an interlock, fitted by an electrician, to power circuits in the house safely.
The very large portables
Generac also makes the GP15500EFI and GP18000EFI, at 15,500 and 18,000 running watts. They can start central air. They also weigh more than 420 pounds and use a 14.2-gallon fuel tank. At that size, most homeowners are better served by a standby unit. These machines make more sense on farms and job sites.
Step 3: Air-Cooled Standby, 10 to 28 kW
A standby generator is installed permanently outside the house, like a central air conditioner. It runs on natural gas or propane and starts by itself within seconds of an outage. Generac says it is the leading maker of home standby generators.
| Size | Rating on propane | Rating on natural gas | Amps at 240 V | Weight | Typical home |
|---|---|---|---|---|---|
| 10 kW | 10 kW | 10 kW | About 42 | 334 lb | Essentials in a small home |
| 14 kW | 14 kW | 14 kW | About 58 | 391 lb | Essentials plus one air conditioner |
| 18 kW | 18 kW | 17 kW | About 75 | 426 lb | Most of a mid-size home |
| 22 kW | 22 kW | 21 kW | About 92 | 451 lb | A whole home with central air |
| 24 kW | 24 kW | 22.5 kW | About 100 | 461 lb | A whole home with extra loads |
| 26 kW | 26 kW | 24 kW | About 108 | 524 lb | A large home |
| 28 kW | 28 kW | 25 kW | About 117 | 524 lb | A large home with several big loads |
Generac’s own guidance fits this table. It says smaller homes may need 10 to 18 kW, and larger homes with more than one air conditioner may need 22 to 28 kW.
Why a smaller standby unit can run a bigger house
A standby generator works with a transfer switch, and the switch can do some thinking. Generac’s Load Manager holds back large appliances so they do not all start together. With load management, an 18 or 22 kW unit can serve a home that would overload it if everything ran at once.
That means there are two honest ways to size a standby generator. You can buy enough kilowatts to run everything together. Or you can buy fewer kilowatts and let load management share them out. The second is cheaper to buy and cheaper to fuel.
Our guide to Generac standby generators compares the standby range in detail.
Step 4: Beyond 28 kW
Generac’s standby catalog continues far above the air-cooled range. Its site lists larger gaseous models at 22, 25, 27, 30, 32, 40, 48, 60, 80, 100, 130 and 150 kW, in single-phase and three-phase versions. It also lists diesel standby generators at 15, 20, 30, 48 and 50 kW.
These larger units are liquid-cooled, like a car engine. They suit very large homes, homes with 400-amp service or all-electric heating, and businesses. They are quoted and installed by dealers. Generac notes that not every dealer is trained for liquid-cooled models, so ask.
What Moves You Up or Down a Size
The chart gives a starting point. Five things can shift you from it.
- Altitude. Engines lose roughly 3% of their power for every 1,000 feet above sea level. At 5,000 feet, a 7,000-watt generator behaves more like a 6,000-watt one.
- Fuel. Dual fuel portables make about 10% less on propane than on gasoline. Larger Generac standby units are rated lower on natural gas than on propane.
- Motor starting. A soft-start kit on an air conditioner cuts its starting surge, which can let a smaller generator do the job.
- 240-volt loads. A well pump, central air or a dryer needs a generator with a 240-volt outlet, not just more watts.
- How you live in an outage. If you are happy to run the microwave and the well pump at different times, you need less.
Tip: measure instead of guessing
A plug-in power meter shows the real running watts of any 120-volt appliance. Measure your refrigerator, freezer, sump pump and electronics for a few days. Real figures are often lower than chart figures, and they may put you a full step down the ladder.
Safety at every size
Size does not change the basic rules. Run any portable generator outdoors only, at least 20 feet from the house, with the exhaust pointing away from doors, windows and vents. Never run one in a garage. Never plug a generator into a wall outlet. Connecting to house wiring needs a transfer switch or an interlock fitted by a licensed electrician. A standby generator must be installed to the maker’s clearances and local code. Fit carbon monoxide alarms on every level of your home.
One Generac at Each Step
We have not tested these products. Details come from Generac’s pages and the Amazon listings, and stock changes quickly.
Start here
P3 P4400 Kill A Watt Electricity Usage Monitor
A plug-in meter that shows how many watts a 120-volt appliance really uses. It is the cheapest way to size a generator from facts instead of charts.
- DisplaysVolts, amps, watts, kilowatt-hours
- Accuracy on listingWithin 0.2 to 2.0%
- For115-volt AC appliances
- Capacity15 amps
- DisplayLCD
- Warranty1 year limited
- Why it works: it measures the actual draw of your own refrigerator, freezer and sump pump.
- Who it is best for: anyone choosing between two generator sizes.
- What it solves: buying a size too big, or too small, because a chart did not match your appliances.
- Keep in mind: it works only on 120-volt plug-in appliances. It cannot measure a well pump, central air or anything hard-wired. For those, read the nameplate or ask an electrician.
As an Amazon Associate we earn from qualifying purchases. Details come from the Amazon listing, checked October 2026.
Essentials with a well pump
Generac GP5500E Portable Generator with EFI and Electric Start (6,875 Starting Watts)
A mid-size open-frame generator with electronic fuel injection. The listing gives a starting capacity of 6,875 watts and up to 11 hours of run time at half load.
- Running / starting watts5,500 / 6,875
- Engine298 cc OHV with EFI
- StartElectric, battery included
- Run timeUp to 11 hours at 50% load
- SafetyCOsense shutdown, low-oil shutdown
- Weight163 lb on the listing
- Why it works: fuel injection means no carburetor to gum up between outages and no choke to set.
- Who it is best for: homes that need the refrigerator, furnace, lights and a 1/2 hp well pump.
- What it solves: hard starting after months in storage, which is the classic portable generator problem.
- Keep in mind: it will not run central air. It is an open-frame unit, so it is loud. Shipping took a few days when we checked.
As an Amazon Associate we earn from qualifying purchases. Specs come from Generac’s product page and the Amazon listing, checked October 2026.
Largest practical portable
Generac GP9500E Tri Fuel Portable Generator with EFI and Electric Start (12,500 Starting Watts)
A large portable that runs on gasoline, propane or natural gas. It has both 30-amp and 50-amp 240-volt outlets for a transfer switch.
- Running watts9,500 gas, 8,550 propane, 7,000 NG
- Starting watts12,500
- Outlets30 A and 50 A at 120/240 V, plus GFCI duplex
- Run timeUp to 10.5 hours at 50% load on gasoline
- StartElectric, with recoil backup
- Warranty on listing3-year residential
- Why it works: it is as much power as most homes can use from a portable, with three fuel choices.
- Who it is best for: larger homes that want most essentials on a 50-amp transfer switch.
- What it solves: running out of one fuel in a long outage.
- Keep in mind: it weighs about 220 pounds. Output drops on propane and again on natural gas, so size against the fuel you will use.
As an Amazon Associate we earn from qualifying purchases. Specs come from the Amazon listing, checked October 2026.
Smallest automatic system
Generac 14 kW Whole Home Generator with Transfer Switch and Cellular Monitoring
A 14 kW air-cooled standby generator sold with a transfer switch. It starts by itself and runs on natural gas or propane.
- Rating14 kW on LP and on NG
- Amps at 240 VAbout 58
- EngineGenerac G-Force 800
- Natural gas at half load189 cubic feet per hour
- Weight391 lb
- Warranty on listing5-year limited
- Why it works: automatic start, no refueling and enough power for essentials plus one air conditioner.
- Who it is best for: smaller homes, and anyone who is often away when the power fails.
- What it solves: a flooded basement or a thawed freezer while you are at work or on holiday.
- Keep in mind: installation, permits and gas work are extra and usually cost as much as the generator. Remote monitoring needs a Mobile Link subscription.
As an Amazon Associate we earn from qualifying purchases. Specs come from Generac’s product pages and the Amazon listing, checked October 2026.
Whole-home favorite
Generac 22 kW Whole Home Generator with Transfer Switch and Cellular Monitoring
The size most often chosen for whole-home backup. Generac rates it at 22 kW on propane and 21 kW on natural gas.
- Rating22 kW on LP, 21 kW on NG
- Amps at 240 VAbout 92
- EngineGenerac G-Force 1000
- Natural gas at half load221 cubic feet per hour
- Weight451 lb
- Warranty on listing5-year limited
- Why it works: 92 amps covers a typical home with central air, and load management stretches it further.
- Who it is best for: family homes with 200-amp service and one or two air conditioners.
- What it solves: choosing which circuits to live without. With this size, most homes do not have to.
- Keep in mind: it needs a gas supply of about 311 cubic feet an hour at full load. Have the meter and pipe checked. Stock was limited when we looked.
As an Amazon Associate we earn from qualifying purchases. Specs come from Generac’s product pages and the Amazon listing, checked October 2026.
Portable or Standby: Where Is the Line?
| Question | A portable is enough if | A standby unit makes sense if |
|---|---|---|
| Who is home? | Someone is usually home in an outage | The house is often empty |
| How often? | Outages are rare and short | Outages are frequent or last days |
| What must run? | Refrigerator, furnace, pumps, lights | Central air, electric heat, medical equipment |
| Who refuels? | You can carry and store fuel | You want fuel piped in |
| Budget | Lower cost matters most | Convenience and coverage matter most |
Our guide to portable vs standby generators goes through the choice in detail, and Generac power generators compares the product families.
Common Mistakes When Sizing a Generac (and the Fix)
Pro Tips for Choosing a Size
- Start with the must-haves. A sump pump or medical device sets the minimum. Comfort loads come second.
- Stagger big loads. Starting the largest motor first and adding loads one by one lets a smaller generator cope.
- Check your panel. The breaker sizes on your largest appliances tell you a lot about their demand.
- Think about next year. A planned heat pump, well or EV charger should go on the list now.
- Ask about load management before you buy a larger standby unit. It may save you a size.
- Compare fuel use, not just price. A bigger generator burns more every hour it runs.
- Use Generac’s free quote for standby units. Generac says a dealer quote includes sizing options.
Real-Life Scenarios: Find Yourself on the Ladder
These are typical situations. They are examples to help you choose, not reports from real customers.
🏢 The townhouse
Gas heat, city water, no sump pump. You want the fridge, the furnace fan, lights and the internet.
About 2,100 running watts, plus the furnace blower’s starting surge. A 3,000-watt inverter or the GP3600 covers it.
Step: 1 or 2
🏡 The country home on a well
You need the well pump, the furnace, a freezer and the kitchen basics, and you are home most days.
About 3,800 running watts before kitchen appliances, with a 240-volt pump. A 5,500 to 8,000-watt portable and a transfer switch fit.
Step: 2
🏠 The family home with central air
Two adults work away from home, and summer outages last days.
Central air and an empty house both point to automatic power. A 22 kW standby unit covers it.
Step: 3
Generac Generators: FAQ
What sizes do Generac generators come in?
Portable models run from 2,200 to 18,000 running watts. Air-cooled home standby models come in 10, 14, 18, 22, 24, 26 and 28 kW. Larger liquid-cooled standby models go up to 150 kW, and Generac also lists diesel standby units from 15 to 50 kW.
What size Generac generator do I need to run my house?
For essentials such as the refrigerator, furnace and pumps, about 3,600 to 8,000 running watts is typical. For a whole home with central air, Generac suggests 22 to 28 kW for larger homes and 10 to 18 kW for smaller ones. A dealer load assessment gives the exact figure.
How many amps does a 22 kW Generac produce?
About 92 amps at 240 volts on propane. On natural gas it is rated at 21 kW, which is about 88 amps.
Will a Generac portable generator run central air?
Most will not. A 24,000 BTU central air conditioner needs about 3,800 running watts and around 11,400 watts to start. That calls for a 14 kW or larger standby unit, one of Generac's largest portables, or a soft-start kit on the air conditioner.
What is the difference between starting watts and running watts?
Running watts is the power a generator supplies continuously. Starting watts is a brief surge for starting motors. Size your generator on running watts, then check that the starting watts cover your largest motor.
Is a bigger Generac always better?
No. An oversized generator costs more to buy and to fuel. Choose the size that covers your running load with about 20% in reserve and handles your largest starting surge.
Your Generac Sizing Checklist
- List the loads that must run at the same time.
- Note which ones need 240 volts.
- Add the running watts.
- Add the largest extra starting load once.
- Add about 20% in reserve.
- Adjust for altitude and for the fuel you will use.
- Find your row on the size chart.
- Decide between manual and automatic operation.
- For a standby unit, ask a dealer for a load assessment and about load management.
- Plan a safe location and a proper connection before you buy.
The bottom line
Generac makes a generator for every rung of the ladder. Add up your running watts, allow for the biggest motor start, and decide whether you need it to run by itself. The right model follows from those three answers.
As an Amazon Associate we earn from qualifying purchases.
Sources: Generac product pages and specification tables for portable and home standby generators, and Generac’s home standby pages (generac.com); typical appliance wattages in line with commonly published charts, as used in our generator sizing guide; Amazon listings for the Kill A Watt P4400, Generac GP5500E, GP9500E Tri Fuel and Generac 14 kW and 22 kW standby generators. All checked October 2026.
