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Last Updated on September 25, 2021

Running an air conditioner can require a lot of power, but as long as you have the right generator you can run A/C anywhere! In order to run safely and efficiently, you’ll need to look at your air conditioner’s BTU, and then choose the right size generator with that information.

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## What Is BTU?

Before we get into generator sizes and air conditioner compatibility, let’s quickly discuss what BTU stands for. BTU stands for British Thermal Unit. One BTU tells you how much energy your A/C unit takes to raise the temperature of 1 pound of water by one degree (in Fahrenheit). Higher BTU numbers indicate a more powerful A/C system.

## What Generator Do I Need For A 5000 BTU Air Conditioner?

A 5000 BTU air conditioner is the smallest or least powerful type of A/C unit available. This means that you can successfully run it on a smaller generator. Not all 5000 BTU air conditioners are created equal, however. You’ll need to look at the specs for yours to determine the size of the generator you’ll need.

There are two ways to go about finding the minimum wattage your generator will need to run your A/C unit.

### 1. Calculate Using the EER Rating

The EER of an A/C unit stands for the Energy Efficiency Ratio. This number should be available in the Energy Guide that comes with your unit. This number tells you how energy efficient your A/C unit is. The higher the EER rating, the more efficient (and the lower the Watts needed) the unit is.

If you break it down into layman’s terms, the EER rating tells you how much BTU cooling effect the A/C unit will give you for each 1 W of power. For example, an EER rating of 10 would tell you that for each 1 W of power given to the unit, you’ll receive 10 BTU of cooling effect in return.

For a lower efficiency unit with an EER rating of 8, you’d only receive 8 BTU of cooling effect for the same amount of energy. In other words, lower efficiency units (with lower EER ratings) require more energy to produce the same BTU of cooling effect as higher efficiency units.

To find the ideal wattage of your generator, you’ll need to plug your EER rating and the BTU number into the following formula:

**BTU / EER rating = Watts needed**

For example, if you had a lower efficiency 5000 BTU A/C unit with an EER rating of 8, you would calculate as follows:

**5000 BTU / 8 = 625 W**

Meaning that you would need a generator with a minimum capacity of 625 Watts.

For a standard efficiency A/C unit with an EER rating of 10, you’d follow the same calculations:

**5000 BTU / 10 = 500 W**

For this unit, a 500 W generator would be sufficient. You’ll find that most modern 5000 BTU units can function on a 500 W generator.

Lastly, for a high-efficiency model with an EER rating of 12.5, here’s what you’d find:

**5000 BTU / 12.5 = 400 W**

This is a helpful calculation to keep on hand when you’re trying to determine the size of the generator you’ll need for your A/C unit.

### 2. Calculate Using the SEER Rating

Some units won’t have a listed EER rating but instead will tell you the SEER rating. This might seem like the same thing, but it’s slightly different. While EER ratings tell you the Energy Efficiency Ratio of your unit, SEER ratings tell you the Seasonal Energy Efficiency Ratio. Companies can find the SEER rating by taking the average EER ratings across a range of outdoor temperatures— in other words, they average the EER ratings they get at different times of year.

Just like with EER ratings, a higher SEER rating will tell you that your unit is more energy-efficient and will therefore need a generator with a lower wattage capacity. Because the SEER rating and the EER rating are slightly different, you can use the SEER rating to find the EER rating. Once you’ve done this, all you have to do is plug the EER rating into the formula above.

It’s important to use this formula to find the EER rating from the SEER rating— they are not interchangeable! Here’s why:

If you used the SEER rating in the formula above for a low-efficiency unit (SEER rating of 9.138) you would find that you need about 500 W for your generator. In reality, you would actually need a 625 W generator, and purchasing the smaller one could lead to all sorts of problems.

Instead, always follow this formula to find an EER rating from a SEER rating:

**SEER Rating / 1.1423 = EER Rating**

In this formula, 1.1423 is kind of like the magic number that never changes. Let’s calculate the same examples as above.

A low-efficiency unit with a SEER rating of 9.138:

**9.138 / 1.1423 = 8**

Then, you would use the 8 in the original formula from section 1.

For a standard efficiency unit with a SEER rating of 11.423:

**11.423 / 1.1423 = 10**

And, lastly, a high-efficiency unit with a SEER rating of 14.279

**14.279 / 1.1423 = 12.5**

## Conclusion

These are both really helpful formulas if you want to be as specific and accurate as possible when choosing the size of your generator for your A/C unit. If you don’t feel up to the challenge (or can’t figure out the EER and SEER ratings), don’t worry. A safe bet is that a standard 5000 BTU air conditioner unit will need 500 W of power from your generator.

There are definitely some cases where this is not true and the unit requires a larger generator, though. Most commonly, this occurs in situations where the A/C unit is on the older side and therefore less energy-efficient than most newer models.