what size generator to run my ac

What Size Generator Do I Need to Run My AC?

A hurricane-season planning estimate for the generator size needed to run your central AC and household essentials — accounting for the compressor's start-up surge.

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Direct answer

A central AC needs both its running watts and a much larger start-up surge; add household essentials, and a typical home lands in the 10-20 kW range unless a soft-start kit lowers the surge.

Why this matters

Use this before storm season to plan a standby or portable generator that can actually start your AC, not just run the lights.

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This page gives an educational planning result. Final quote, rebate, payment, package, and installer details wait until the customer and home record are saved inside the assessment flow.

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Live result

Plan on roughly a 14 kW generator

Running a 3-ton AC plus typical essentials needs about 13,920 starting watts.

Recommended generator

14 kW

Peak / starting watts

13,920 W

Running watts

7,200 W

Soft-start

Not installed

A generator must cover the AC's brief start-up surge, not just its steady running load. This is a hurricane-season planning estimate; an electrician confirms the actual sizing and transfer-switch setup.

Ask about an AC soft-start kit: it cuts the start-up surge and can let a smaller generator start the system.

For whole-home backup, an electrician sizes the generator and a transfer switch to your actual panel and loads.

This is a planning estimate, not a final quote or engineering report. Field conditions, permits, equipment selection, ducts, electrical work, and installer verification can change the result.

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Sources and assumptions

How this estimate is grounded.

The visible result, assumptions, and schema match. Structured data does not claim anything that is not also shown on the page.

Source

U.S. Department of Energy central AC efficiency guidance

DOE/FEMP publishes hot-humid SEER2 examples and lifecycle energy cost assumptions.

Open source Source

ENERGY STAR Heat & Cool Efficiently

ENERGY STAR notes HVAC is nearly half of household energy use and gives filter, duct, thermostat, and replacement guidance.

Open source

Common questions

Short answers for homeowners.

What size generator do I need to run a 3-ton AC?

A 3-ton central AC draws roughly 3,500-4,500 running watts, but its compressor start-up surge is much higher. With household essentials, many homes need a 10-14 kW (or larger) generator — though a soft-start kit can lower the surge enough to use a smaller unit.

Why does my AC need so much more to start than to run?

The compressor draws a large inrush of current the instant it starts (the locked-rotor surge), often two to three times its running draw. The generator has to handle that peak, not just the steady running load.

Does a soft-start kit let me use a smaller generator?

Often, yes. A soft-start kit ramps the compressor up gradually and cuts the start-up surge substantially, which can let a smaller generator (or one already powering other loads) start the AC.

A calculator can narrow the decision. A saved assessment can price the real home.