What Size Air Conditioner Do I Need? - Rinaldi's Air Conditioning & Heating

What Size Air Conditioner Do I Need?

How rooms and home size can affect air conditioner requirements.
Read Time: 7 minutes
Jan 3, 2021

Air conditioner size needs depend on the size of your home and the placement of your unit. An air conditioner needs 20 BTU to properly cool each square foot of living space in your home. Other variables like windows and ceiling height can play into needing more or less BTU per square foot. Most units will range from 5,000 to 12,500 BTU. A small office can make do with the lower end of the scale while an open floor plan will need the higher end.

Why You Need a Correctly Sized Air Conditioner

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


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.

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 20.


For freestanding, wall, or window units, the cooling capacity can range from 5,000 BTUs to 8,500 BTUs. You would need to measure the size of the room in which the unit will be placed to calculate what size you need.

A small bedroom will be under 300 square feet and require less than 6,500 BTU to cool. A master bedroom, on the other hand, may be up to 400 square feet and need 8,500 BTU to properly cool.

You’ll need to make some adjustments for the characteristics of the room as well. If it’s sunny or shady, if multiple people 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.


Homes and open floor plan spaces will need to have a higher BTU to cool. Usually around 12,500 BTU. You’ll need to have the square footage of your home to find the best air conditioner for your space.

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 A/C BTU calculators will ask for your zip code so they can automatically factor in location for you.

Measurements are sometimes in tons, which correspond to a specific number of BTUs. One 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.

To calculate for yourself how big of a central air conditioning unit you need, multiply your home’s total square footage by 20. 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.


Professional repairman checking air conditioning unit
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.


AC size isn’t something to disregard. It can directly play into every cost associated with running air conditioning in your home, from initial installation cost to the cost of purchase. It can also be related to the durability of the unit, depending on how well you match your unit size to the needs of your home. Plus, utilities can vary depending on the size of the AC unit selected.


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.


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.

This doesn’t mean you should opt for a smaller unit to save on costs. It won’t be able to keep up with the needs of your room leading to discomfort for the home’s inhabitants and aggravating maintenance calls down the road.


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. Installation cost is something to be considered when purchasing your unit. You don’t want the nasty surprise of an unexpected and high installation fee.
Man installing ac unit


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, but the option for professional help is there if you need it.

If you opt to DIY installation of a freestanding or window unit you can save on installation costs but run the risks of incorrectly installing it yourself which can lead to future problems with cooling your home.

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 number of permits required and necessary specialized knowledge a professional will already be equipped to handle. A professional HVAC technician will 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, making installing a central air conditioner on your own an inefficient option.


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 normally would have. This process is called short cycling and affects the lifespan of the air conditioner due to the unit constanting starting up and shutting off.


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, 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.
Air conditioner repair man checking levels


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.

Even an AC unit from a trusted brand will fall flat if it is the incorrect size for the space it’s meant to cool.


The larger the air conditioning unit, the more energy it takes to power it. However, smaller units will run constantly if being forced to cool a space larger than their capacity making it an insufficient solution to cutting down on energy usage. Likewise, 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. If you’re concerned about energy efficiency you can pair a properly sized unit with energy efficient habits to cut costs year-round.


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 close reach. Wall units and central air may have parts that need to be maintained that are more difficult to easily get to.

It is recommended that you have your AC unit professionally services once to twice a year. This will help catch small problems and wear-and-tear before it turns into a pricey repair.


It can be safe to purchase an air conditioner online, as long as you properly do your research and 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. You should only buy from reputable stores and make sure you’ve thoroughly read the warranty.

To ensure proper installation of a correctly sized unit, contact one of our professional HVAC technicians today.

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