What Size Generator To Run Central Air? All Sizes Considered!

Choosing a generator of the right size is essential to ensure an uninterrupted power supply to your appliances within the budget. When it comes to central air, choosing a generator size can seem confusing. 

So, what size generator to run central air? 

To run a 1.5-ton central air generator, you need a 6000-watt portable or standby generator, given that you only use the AC. To run a 2-ton central air, you must buy 8000 watts portable or standby generators. A 3-ton generator requires a 12000 watts standby generator. And for a 4-ton and 5-ton central air, respectively 15000 watts and 18000 watts standby generators are recommended. 

To understand this discussion in detail, keep reading.

How to Calculate Generator Size for Central Air?

Calculate Generator Size for Central Air

To calculate the right generator size for your central AC, you have to find out the surge wattage of the central air. And then choose a generator that has more wattage capacity than that. 

Surge wattage is the initial power that your AC needs when it starts. When the AC runs, it requires 2-3 times less power than the surge power. So, taking the generator with a higher capacity than the surge power can back up your central air. 

Here’s the formula to calculate the generator size. 

AC Wattage = AC Ton x 3,500 watts (1 ton AC requires 3500 watts of surge power)

If the AC capacity is mentioned in BTU, just divide it by 12000 and you will get the AC capacity in tons, As 1 Ton = 12000 BTUs

Then choose a generator with more kW than this outcome. 

Also, if you want to run other electronic items in your house with the generator, calculate the wattage of those items and take a generator to cover the total wattage. 

What Size Generator to Run Central Air?

Here’s the table for different central AC sizes and the recommended generator sizes. For this table, let’s assume, you will only use the central air with the generator and nothing else. 

Ac SizeGenerator SizeRecommended Generator Type
1.5 tons or 18,000 BTUs6 kWPortable or standby
2 tons or 24000 BTUs8 kWPortable or standby
3 tons or 36000 BTUs12 kWStandby
4 tons or 48000 BTUs15 kWStandby 
5 tons or 60000 BTUs18 kWStandby 

What Size Generator To Run 1.5-Ton Central Air?

To run a 1.5-ton or 18,000 BTUs central air, you will need at least 6000 watts or a 6 kW generator. Let’s see the math breakdown here. 

1.5 ton AC Wattage = 1.5 x 3,500 watts =  5250 watt. 

So, for our generator, we need at least 5250 watts. However, there are other factors to consider. Due to climate conditions and generators’ power loss, it’s not always possible for a 5250 watts generator to provide the same power all the time. 

In that case, to make the generator safe for appliances, having a generator with slightly more power is better. So, for this central air, a 6000-watt generator is recommended. 

For this AC size, you can choose either a portable or standby generator as both are available in this power. 

What Size Generator To Run 2-Ton Central Air?

What Size Generator To Run 2-Ton Central Air

At least 8 kW or 8000 watts generator is required to power a 2 ton or 24000 BTUs central air. 

2 ton AC Wattage = 2 x 3,500 watts = 7000 watts. And to be safe, you should take a generator with 8000 watts portable or standby generator. 

What size generator to run 3-ton central air?

To run a 3-ton or 36000 BTUs central air, you are going to need at least 12 kW of a standby generator. 

3 ton AC Wattage = 3 x 3,500 watts =  10500 watt. You might also like to run other devices with this generator. 

So, to be on the safe side, a high-quality 12000 watts standby generator like a Pulsar 12000-watt generator is recommended here. A portable generator is not powerful enough to take this much load. 

What Size Generator To Run 4-Ton Central Air?

To run a 4-ton or 48000 BTUs central air, you are going to need at least 15 kW of a standby generator. Here, you can not use a portable generator as a portable generator can not power more than 12000 watts. 

What Size Generator To Run 5-Ton Central Air?

What Size Generator To Run 5-Ton Central Air

If you want to run a 5-ton or 60000 BTU central air, you will require a generator with at least 18 kW of power. For a 5-ton central air, you must go for a standby generator. You might need a different powered generator for a 5-ton regular AC


My discussion on what size generator to run central air ends here. I hope this article could cover all of your needs. If your central AC size is not mentioned here, you can simply use the formula given here and determine your generator need. 

That’s all for now. All the best and goodbye!

Frequently Asked Questions (FAQs):

What if you Choose the Wrong Size Generator?

If you choose the wrong size generator for your central air, it can cause several problems. If the generator is underpowered, it will provide insufficient power to the AC and the AC will face sudden voltage drops. As a result, the AC can even get damaged. Also, it can damage the generator itself. Using an overpower generator is costly. 

What Is The Difference Between Portable And Standby Generators? 

Portable generators are smaller and lighter than the standby generator. Unlike standby generators, portable ones are only capable of backing up small appliances. Also, portable generators are noisier than standby generators. Standby generators are more costly and more complicated to install than portable generators. 

How Much Do Generators Cost?

The generator product depends on its size, type, brand, and other features. On average, 7 to 10 kW generators cost around $2,300 – $3,500. 13 to 16 kW generators cost $3,500 – $4,800. If you are looking for a generator of 17 to 20 kW, it will cost you around $4,000 – $6,200. 

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