TL;DR
A 5,000 BTU window AC needs a 1,200W generator, a 10,000 BTU unit needs 2,400W, and a 15,000 BTU unit needs 3,500W. Always factor in the starting surge (approximately 2x running watts).
AC Starting Surge: The Most Common Generator Sizing Mistake
Air conditioners have compressor motors that require a significant surge of power to start — typically 2-3 times their running wattage. This is the most common reason generators fail to power AC units. A 10,000 BTU window AC might draw 1,200W while running, but it can spike to 2,400W or more when the compressor kicks on.
The key is to size your generator for the starting watts, not the running watts. If you want to run a window AC plus a refrigerator and some lights, you need a generator that can handle all the running watts plus the highest single starting surge — which is almost always the AC compressor.
For most homeowners who want to run a 10,000 BTU window AC plus basic essentials (fridge, lights, fan), a 3,500W generator provides comfortable headroom.
Top picks for this size
Yamaha EF3000iSEB, 2800 Running Watts/3500 Starting Watts, Gas Powered Portable Inverter #ad
★★★★☆ 4.7 · 30 · $1550
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YAMAHA EF3000iS, 2800 running Watts/3000 Starting Watts, Gas Powered Portable Inverter #ad
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Generac 6864 XD5000E 5000-Watt Diesel-Powered Portable Generator - Ideal for Emergency Backup Power and Job Sites - Reliable Power for Demanding Applications - CARB Compliant #ad
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Westinghouse 5000 Peak Watt Super Quiet Portable Inverter Generator, Remote Electric Start with Auto Choke, Wheel & Handle Kit, RV Ready, Gas Powered, Parallel Capable #ad
★★★★☆ 4.7 · 5K+ ·
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Westinghouse 4650 Peak Watt Dual Fuel Portable Generator, Remote Electric Start with Auto Choke, RV Ready 30A Outlet, Gas & Propane Powered #ad
★★★★☆ 4.7 · 740+ · $440
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WEN Super Quiet 3800-Watt RV-Ready Portable Inverter Generator with Fuel Shut-Off and Electric Start (56380i) #ad
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EGO POWER+ Portable Power Station, 3000W, Battery Powered, Inverter Generator for Home and Outdoor, Battery and Charger Not Included - PST3040 #ad
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WEN Super Quiet 2350-Watt Portable Inverter Generator with Fuel Shut Off, Gasoline Power, Ultra Lightweight (56235i), Black #ad
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★★★★ 4.2 · 2K+ · $874
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Briggs and Stratton 30747 3500 Watt Portable Generator 208cc OHV w/twistlock #ad
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Honda EU3000iS 3000 Watt Inverter Generator, Super Quiet 120V Gas Powered Portable Generator for Camping, RV or Home Backup Power Supply, Up to 19.6 Hour Run Time (EU3000IS1AN) #ad
★★★★☆ 4.6 · 112+ · $2399
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DuroMax XP2300iH 2,300-Watt Dual Fuel Portable Digital Inverter Generator - Gas & Propane, RV & Emergency Ready #ad
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Westinghouse 2800 Peak Watt Super Quiet & Lightweight Portable Inverter Generator, Gas Powered, CO Sensor, Parallel Capable, Long Run Time #ad
★★★★ 4.3 · 440+ ·
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Westinghouse 5000 Peak Watt Super Quiet Dual Fuel Portable Inverter Generator, Remote Electric Start, Gas & Propane Powered, RV Ready, CO Sensor, Parallel Capable #ad
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Westinghouse 5000 Peak Watt Super Quiet Dual Fuel Portable Inverter Generator, Remote Electric Start, Gas & Propane Powered, RV Ready 30A Outlet, Parallel Capable, Blue/Black #ad
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Westinghouse 2800 Peak Watt Super Quiet & Lightweight Portable Inverter Generator, Gas Powered, Parallel Capable, Long Run Time #ad
★★★★ 4.2 · 3K+ · $549
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Champion Power Equipment 3500-Watt Portable Inverter Generator with Quiet Technology and CO Shield #ad
★★★★☆ 4.6 · 205+ · $600
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Generac 3,300-Watt Gas Powered Portable Inverter Generator - Lightweight and Compact - USB Ports for Device Charging - Produces Clean, Stable Power - Great for Home Backup, Camping, and RV Use #ad
★★★★ 4 · 154+ ·
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Pulsar PGD40ISCO Ultra Light Quiet 4000W Portable Gas Inverter Generator, white #ad
★★★★ 4.2 · 467+ · $423
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WEN 3600-Watt Portable Inverter Generator, RV-Ready, Quiet and Lightweight with Fuel Shut Off (56360i) #ad
★★★★ 4.2 · 567+ · $396
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WEN 4800-Watt Portable Inverter Generator, Electric Start, RV-Ready, Quiet and Lightweight with Fuel Shut Off and CO Watchdog (56480iX) #ad
★★★★ 4.2 · 171+ · $679
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WEN Quiet and Lightweight 4800-Watt RV-Ready Portable Inverter Generator with Fuel Shut Off (56477i) #ad
★★★★☆ 4.7 · 444+ · $555
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Champion Power Equipment 5000-Watt Electric Start Tri Fuel RV Ready Portable Generator with Free 3-Year Warranty #ad
★★★★☆ 4.8 · 98 · $688
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Champion Power Equipment 2500-Watt Ultralight Portable Inverter Generator with Quiet Technology and Free 3-Year Warranty #ad
★★★★ 4.2 · 256+ · $549
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Champion Power Equipment 4500-Watt RV Ready Portable Inverter Generator with Quiet Technology and Free 3-Year Warranty #ad
★★★★★ 5 · 168+ · $679
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Champion Power Equipment 4500-Watt Wireless Remote Start Inverter Generator with Quiet Technology and Free 3-Year Warranty #ad
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Westinghouse 4000 Peak Watt Super Quiet Dual Fuel Portable Inverter Generator, Remote Electric Start, Gas & Propane Powered, RV Ready, CO Sensor, Parallel Capable #ad
★★★★☆ 4.6 · 2K+ · $549
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Champion Power Equipment 2500-Watt Dual Fuel Portable Inverter Generator with Quiet Technology and CO Shield #ad
★★★★☆ 4.6 · 136+ · $584
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Champion Power Equipment 4000-Watt RV Ready Portable Inverter Generator with Quiet Technology and Free 3-Year Warranty #ad
★★★★ 4.2 · 353+ · $585
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Champion Power Equipment 4000-Watt Dual Fuel RV Ready Portable Inverter Generator with Quiet Technology and Free 3-Year Warranty #ad
★★★★ 4.2 · 248+ · $719
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Generac 3,300-Watt Gas Powered Portable Inverter Generator - Lightweight and Compact - USB Ports for Device Charging - Produces Clean, Stable Power - Great for Home Backup, Camping, and RV Use #ad
★★★★☆ 4.6 · 154+ ·
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AMERISUN 4500W Open Frame Inverter Generator, 3800 Running Watts Portable Gas Powered Generator with CO Alert, RV Ready, Parallel Ready, Eco Mode, 223cc Engine for Home Backup, Camping & Emergency Use #ad
★★★★ 4.2 · 435+ · $210
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AFERIY 2048Wh Portable Power Station 2400W (Peak 4800W),P210 LiFePO4 Battery Generator,AC Fast Charging, 12V/25A XT60 DC output port,UPS Power Outages,Home Backup,Camping(Solar Panel Optional) #ad
★★★★☆ 4.7 · 335+ · $484
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Generac 3,800-Watt Dual-Fuel Portable Inverter Generator - Gas and Propane Compatible - Quiet Operation - Clean, Stable Power - Great for Home Backup, Camping, and RV Use #ad
★★★★☆ 4.6 · 7 · $1049
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Westinghouse 5000 Peak Watt Super Quiet Dual Fuel Portable Inverter EFI Generator, Remote Electric Start, Gas & Propane Powered, RV Ready, CO Sensor, Parallel Capable, CARB Compliant #ad
★★★★☆ 4.7 · 80 · $1249
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Champion 3650-Watt RV-Ready Portable Generator with CO Shield #ad
★★★★☆ 4.6 · · $420
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Oxseryn 5000W Inverter Generator Gas Powered, Open Frame Generator, Portable Outdoor Power Equipment, Emergency Home Backup, RV Ready 30A Outlet, ECO Mode, EPA Compliant #ad
★★★★★ 5 · 304+ · $323
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Champion Power Equipment 5500-Watt RV Ready Portable Generator | Open Frame Inverter, Quiet Technology, 3-Year Warranty, CARB Compliant #ad
★★★★☆ 4.5 · · $679
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PowerSmart 3800 Watt Dual Fuel Inverter Generator, Quiet Portable Gas Propane Powered with CO Sensor and RV, 149cc 4-Stroke OHV Engine for Home Backup, Camping and Tailgating #ad
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Anker SOLIX C2000 Gen 2 Portable Power Station, 2,400W (Peak 4,000W) Solar Generator, Full Charge in 58 Min, 2048wh LiFePO4 Battery for Home Backup, Power Outages, and Camping (Optional Solar Panel) #ad
★★★★★ 5 · 365+ · $800
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Oxseryn 5000-Watts Portable Inverter Generator, Gas Generator for Home Backup, 30A Outlet, RV Ready, ECO Mode, 60Lbs, EPA Compliment #ad
★★★★★ 5 · 14 · $304
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These Amazon-available picks meet the calculated spec. For region-specific or licensed contractor-installed options, consult a local professional. See our Disclaimers.
Generator Sizing Guide by AC Unit Size
- 5,000 BTU window AC (small bedroom): 500W running, ~1,200W starting → 1,500W generator
- 8,000 BTU window AC (large bedroom/small living room): 800W running, ~1,800W starting → 2,500W generator
- 10,000 BTU window AC (living room): 1,200W running, ~2,400W starting → 3,500W generator
- 12,000-15,000 BTU window AC (large room/garage): 1,500W running, ~3,500W starting → 5,000W+ generator
Frequently asked questions
What size generator runs a window AC unit?
Yes, as long as the generator can handle both running watts plus the highest starting surge. A 3,500W generator can run a 10,000 BTU window AC (2,400W starting surge) and a refrigerator (600W starting surge) simultaneously, since the surges won't happen at the same time.
Do inverter generators handle AC starting better?
Yes. Inverter generators provide cleaner power and can handle short-duration surges better than conventional generators. For sensitive electronics and AC units, an inverter generator is a better choice.
Should I use a soft start kit for my window AC?
A soft start kit ($100-200) reduces the starting surge of an AC compressor by 30-50%. This can allow a smaller generator to run a larger AC unit. If you're trying to power a 12,000 BTU unit with a 2,500W generator, a soft start kit may make it possible.