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Portable Air Conditioner BTUs: What do they mean and why should I care?

When shopping for a portable air conditioner, you may have come across the foreign acronym “BTU.” It appears not only in every product description but also in many product names. It is obvious that this is important to understanding portable air conditioners, but it is not clear why that is and why it should matter to you.


The acronym stands for British Thermal Unit, which is the unit used to measure thermal (heat) energy. Specifically, it is the amount of energy needed to raise 1 pound of water 1°F at sea level. When used in relation to air conditioning systems, the measurement is expressed in terms of how many BTUs per hour the product can remove from the air. With that said, unless you are involved in the manufacturing or retailing of cooling and heating supplies, this may not mean anything to you. But it should, and here’s why:

Too Much of a Good Thing

A higher number of BTUs isn’t always the answer. Using a portable air conditioner with a BTU level higher than needed can cause the unit to cool quickly, cycle off and then, to maintain your desired temperature, have to cycle on again soon after. By cycling on and off in such fitful spurts of time, your portable air conditioner’s compressor will quickly over-work itself and shorten your unit’s lifespan.

Too Little, Too Late

Using a portable air conditioner with not enough recommended BTUs will keep you from reaching your desired comfort level. The heat load will be too much for your unit, causing it to run continuously and never reach your set temperature level. This is why it is important to pay attention to square footage recommendations in each product’s description.

BTU Recommendations Based on Square Footage:

• Very small spaces (rooms up to 250 sq. ft.) need approximately 7,000 – 8,000 BTUs.

• Medium spaces (rooms 300 – 425 sq. ft.) need approximately 10,000 – 12,000 BTUs.

• Large spaces (rooms 400 – 525 sq. ft.) need approximately 14,000 BTUs.

Other Important Factors to Consider:

Although square footage recommendations are typically correct, there are some other confounding variables that you should pay attention to when looking at portable air conditioner BTUs.

If you are attempting to cool a second story that is typically warmer than the ground floor or a space that gets a lot of direct sunlight (for example, a room with a large west-facing window), you want to add 10% of the recommended BTUs and that is the cooling power you will need. This may mean going up to the next available cooling power.

On the other hand, if the area you are going to be cooling has lots of shade and very little sunlight exposure, you will want to subtract 10% of the recommended BTU.

If there is going to be more than two people in the area at a time, you should add approximately 600 BTUs per additional person.

If you plan on using your portable air conditioner in your kitchen, an area of high heat, you will need to add 4,000 BTUs to the recommended cooling power.

Lastly, you want to consider whether or not your space is open or confined. Our square footage recommendations are meant for confined areas, so if your room open ups into another space without the option of closing a door, you will want to add in that other space. For example, if you want to cool a kitchen that opens into a living room, you will want to combine the size of those two rooms as if they were one space and use that as your determinate square footage.

For help calculating the right BTU for your needs, feel free to give our portable air conditioner experts a call at 1.800.297.6076.

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