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What Size Air Conditioner Do I Need?

What Size Air Conditioner Do I Need?

Having the right size air conditioner is important for adequately cooling your house. If you don’t have the right size, it may not have enough power to cool everywhere. Or it may make your home too cold if you’ve overestimated the size you need. Too large an air conditioner can short cycle, which is turning on and off too frequently, and this will shorten the lifespan of the AC unit.

Whether you’re looking for a central air conditioning system or a wall, freestanding, or window unit, it’s essential to know exactly what you need before you start shopping for one.

Different sizes of air conditioners

Sizes of Air Conditioners

Air conditioners are measured by their cooling capacity in BTUs per hour. BTU stands for British Thermal Unit and is used to measure how much heat a particular air conditioner can remove from the air in the space of an hour.

For a Room

For freestanding, wall, or window units, the cooling capacity can range from 5,000 BTUs to 34,000 BTUs. You would need to measure the size of the room in which the unit will be placed to calculate what size you need.

For a House

For central air conditioning units, the measurements are sometimes in tons, which correspond to a specific number of BTUs. 1 ton is equal to 12,000 BTUs. The smallest standard size is 1.5 tons, which is 18,000 BTUs and the largest is 5.0 tons, which is 60,000 BTUS.

Recommended Air Conditioner Size

To figure out what size air conditioner you need for either a room or a house, you need to know about how much cooling power is needed per square foot. The recommended BTU per square foot is different between central air conditioners and room units, however.

For a Room

In general, a freestanding, wall, or window unit that’s meant to cool just one room should have a capacity of between approximately 20 and 35 BTUs per square foot. However, air conditioners aren’t measured in BTUs per square foot. Most air conditioners will state the total number of BTUs and there are charts and calculators available online detailing which size should correspond with which room dimensions.

You’ll need to make some adjustments for the characteristics of the room as well. If it’s sunny or shady, if there are multiple people who are regularly in that room, or if it’s the kitchen, you’ll need to increase or decrease the capacity of the air conditioning unit accordingly.

Professional repairman checking air conditioning unit

For a House

For a central air conditioning unit, you’ll need to know the square footage of your entire house. Where in the country you live also affects your air conditioning needs. If you live in a northern state, you’ll need less cooling capacity than someone living in a southern state. Online calculators will therefore also ask for your zip code so they can automatically factor in location for you.

To calculate for yourself how big of a central air conditioning unit you need, multiply your home’s total square footage by 30. Divide that total by 12,000. Then subtract 1.0 for the total number of tons you need. If you live in a warmer climate, don’t subtract the 1.0.

How Many Air Conditioners Do I Need?

If you are purchasing a central air conditioner, you should only need one. Central air conditioning units are meant to cool an entire house. Room air conditioning units are generally meant for just the room in which they’re located. If you’re investing in room-specific units instead of central air, you’ll need to decide which rooms need it the most and then purchase an appropriately sized unit for each room.

What Does AC Size Affect?

Air conditioner repair man checking levels


The larger the air conditioner, the more it will cost. This is true whether you’re investing in central air conditioning or whether you’re purchasing individual units for single rooms.

Price Of the Unit

For central air conditioners, prices can start at $3,000 for smaller 2-ton units. Units in the middle of the range can cost about $5,000. Top-end AC units can reach more than $10,000. For single-room air conditioners, either freestanding, wall, or window units, prices can range from $100 to $1,500 depending on what size you need.

Price Of the Installation

If a room unit requires installation, it may cost up to $200. Central air conditioners cost a lot more to install and the cost can run up to $6,000.


The installation process and speed shouldn’t vary much between sizes of air conditioning units. The primary difference is between central air and wall air conditioners. Freestanding and window units may not require professional installation.


Durability is primarily affected if you purchase an air conditioner that is too large. It will cool the room or house too quickly and then shut off, but since it wasn’t able to go through its normal cycle, the heat starts to come back into the room, turning the unit back on sooner than it would have normally. This process is called short cycling and affects the lifespan of the air conditioner.

Cost of Utilities

The larger the air conditioning unit, the higher the cost of your utilities. However, purchasing the incorrect size will also result in much higher utility costs. If your air conditioner is too small, it may run all the time trying to cool a room or home it’s just not powerful enough for. Any money saved in purchasing the smaller unit will be eaten up with the increased utility bills. If your air conditioner is too big, then it will be shutting itself on and off all the time, which doesn’t just harm the durability of the unit but also increases your utility bills.

What Kind of Air Conditioner Is Best?

The best kind of air conditioner is the kind that is the right size for the space you’re wanting to cool. If you want to cool the entire house, a central air conditioner may be more cost-effective than one air conditioner per room. It’s most important, however, to ensure that whatever unit you purchase is the appropriate size, because too large or too small can be problematic.

Energy Efficiency

The larger the air conditioning unit, the more energy it takes to power it. However, it’s not good to have one that is too small because it will run constantly. A unit that is too large won’t run less and will instead short cycle, making it even less energy efficient. The most energy efficient unit is one that exactly fits the needs of the room or house.


The easiest units to self-install are individual room units. Freestanding ones only need to be plugged in. Window units may require a bit more effort in order to properly mount them in the window. Some companies offer installation for wall units, but they’re still possible to install by yourself.

For central air conditioners, it’s generally not recommended that you try to install it yourself. There are a lot of permits required and a lot of specialized knowledge needed that a professional will already be equipped to handle. They would also already be certified. You might save money on the installation, but you’d need to go through a lengthy permit and certification process in order to do it.


Both central air units and single units will require some cleaning and maintenance. Wall and freestanding units may be the easiest to care for because they’re within closer reach. Wall units and central air may have parts that need to be maintained that are more difficult to easily get to.

Is It Safe to Buy an AC Unit Online?

It can be safe to purchase an air conditioner online, so long as you properly do your research. Know exactly what size your home needs. You may want to have a professional come out and make a recommendation to be 100% certain. If a price looks too good to be true, it’s advisable to be wary because it generally is. Buy only from reputable stores and make sure you’ve thoroughly read the warranty.

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