What Size (AC) Air Conditioner Unit do I Need

How Big of an Air Conditioner Do You Need?

There is nothing worse than having to suffer through a brutally hot day with an air conditioner that is not big enough to cool your home. Conversely, an air conditioner that is too large for your home is a waste of money. Fortunately, there are ways of determining exactly what size air conditioner you need.

Calculating Your BTU Usage

The first thing you need to do is calculate how many British Thermal Units (BTUs) your home requires. You can use this handy BTU calculator to determine this.

You will need to perform this calculation for each room in your home, including hallways, closets and vestibules, and then you must add all these numbers together to get your total BTU requirement.

However, if you already know how many square feet your home has, you can also use this handy chart:

100 –   150 square feet: 5,000 BTUs
150 –   250 square feet: 6,000 BTUs
250 –   300 square feet: 7,000 BTUs
300 –   350 square feet: 8,000 BTUs
350 –   400 square feet: 9,000 BTUs
400 –   450 square feet: 10,000 BTUs
450 –   500 square feet: 12,000 BTUs
500 –   700 square feet: 14,000 BTUs
700 – 1,000 square feet: 18,000 BTUs
1,000 – 1,200 square feet: 21,000 BTUs
1,200 – 1,400 square feet: 23,000 BTUs
1,400 – 1,500 square feet: 24,000 BTUs
1,500 – 2,000 square feet: 30,000 BTUs
2,000 – 2,500 square feet: 34,000 BTUs

Choosing an Air Conditioner

When buying an air conditioner, you should select one that either provides or comes close providing the amount of BTUs you home requires. All conditioners are labeled with the amount of BTUs they provide.

Keep in mind, though, that the chart above tells you how many BTUs you will require under ideal conditions. There are a number of variables that can alter this calculation.

Sunlight and Shade

If any of the rooms in your home get a lot of sun, you should raise the BTU requirements of that room by 10%. Conversely, if any of the rooms are well shaded, you can reduce the BTU requirements of that home by 10%.

The Number of Room Occupants

BTU requirements for a room increase based on the number of occupants. BTU calculations in the chart assume that there will be at most 2 people in a room, but if more than two people occupy a room, you need to add 600 BTUs for each additional person.


Kitchens usually contain appliances that generate heat, such as an oven or a stove, and because of this they must have their BTU requirements increased by 4,000 BTUs to offset the heat.

Getting Help

If all these calculations seem overwhelming, all is not lost. You can have a heating, ventilation and air conditioning (HVAC) specialist come to your home to determine exactly what size air conditioner you need and the AC unit cost. Doing this is far better than taking a chance that your new air conditioner will not cool your home properly.

AC Unit Costs

AC Unit Costs

In many parts of the country, such as in the Phoenix area, air conditioning is no luxury. Because of this, if your unit is getting old, you may want to think about buying a new one. The best way of determining how much it will cost you to get a unit that is just right for home is to have a qualified technician visit you, but there are ways in which you can estimate the cost.

The Costs of Air Conditioners Across the United States

Typically, Americans spend anywhere from $5,000 to $8,000 for a new air conditioning system. The average price is a little more than $6,500. Though prices range from a little more than $500 to $12,000.

These prices include not only the cost of the unit itself but also the costs of installing it, which can further include the purchase and installation of air handlers and ducts.

The Costs of Air Conditioners Specifically in the Phoenix Area

Because it is hot in the Phoenix area all year — and because the heat can get extreme in the summer months — the costs of buying a new air conditioning unit here is somewhat different than it is in other parts of the country, such as in the Northeast.

Here are some reasons why:

Better Insulated Homes

In the past, air conditioning systems installed in the Phoenix area had to compensate for the fact that many homes in the area did not have enough insulation and had drafty windows, too. But today, most people in the area have replaced these windows with models that have double or even triple panes. They have also filled in gaps within the windows with caulk, and they have insulated their homes.

The result of this is that people now need smaller air conditioning units than before, and these units not only cost less to buy but also cost less to both run and maintain.

The Need for Efficient Air Conditioning Units

With all the heat in the Phoenix area, the costs of running an air conditioner are as important as its upfront costs. For this reason, having an efficient air conditioner is necessary and these units are not inexpensive.

Efficiency in an air conditioner is based on what is called a Seasonal Energy Efficiency Rating (SEER) number. The larger this number is, the more energy efficient the air conditioner is. With every one-point increase in a SEER number, your energy bills fall 10%. So, even though these air conditioners cost more, in the long run you will save money. This is especially true because energy-efficient air conditioners last longer than ordinary ones, so you do not need to replace them as often.

Local Energy Companies Are Offering Rebates on Air Conditioning Units

Salt River Project (SRP) and Arizona Public Service (APS), which are the two major electric utilities in the Phoenix area, understand the burden electric costs have on the people living there and understand that these costs are driven by the high use of air conditioning in the area.

To offset some of these costs, both companies are currently offering significant rebates on energy-efficient air conditioning units if certified technicians professionally install them. These rebates go as high as $500, and you can receive another $135 if, at the same time of the installation, you have your ducts either repaired or replaced.

Your Next Step

To find out exactly what a new air conditioning unit will cost you, you should ask a qualified technician to come to your home. This technician will not only help you determine the perfect size for your new unit but will also help you select an energy-efficient model. By doing this, you will get an air conditioner that will both keep your home comfortable and keep the expenses of running it at a minimum.