How to Choose the Right Size Air Conditioner - Sky Heating, AC, Plumbing & Electrical (2023)

Size is one of the biggest factors when installing a new air conditioner. If the unit’s capacity is too small, it will run continuously and use more energy, increasing your electric bill. Also, it won’t cool your home very well. And if the AC unit is too large, your space may cool more quickly, but the system won’t run long enough to remove moisture. Your home may then become humid, damp, and clammy, while frequent cycling will burn more energy.

Choosing the right size air conditioner requires knowing the area that needs to be cooled, among other factors.

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Measure Your Space

To start, accurately measure the square footage of your home, room, or space you intend to cool. Multiplying the length of a room by its width gives you its square footage, or area, in square feet (ft2). This value is then multiplied by 25 to estimate the proper air conditioner size in British Thermal Units (BTUs). Using this example, a 12 x 15 foot room is 180 square feet; multiplied by 25 this yields 4,500 BTU of required cooling capacity.

By following this rule, you get ample cooling on a rainy or hot, sunny day. But you can also determine size by considering an A/C needs 20 BTU per square foot. Another method calculates BTU capacity by multiplying square footage by 35, which would yield:

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  • 100 to 150 ft2: 3,500 to 5,250 BTUs
  • 300 to 350 ft2: 10,500 to 12,250 BTUs
  • 450 to 550 ft2: 15,750 to 19,250 BTUs
  • 1,000 to 1,200 ft2: 35,000 to 42,000 BTUs
  • 1,500 to 2,000 ft2: 52,700 to 70,000 BTUs

When estimating capacity, combine the size of rooms not separated by doors. Also consider factors such as ceiling height and window/doorway size; higher values may call for increased cooling capacity. There are other factors as well; per ENERGY STAR recommendations, consider the following:

  • Bright Sunlight: Increase the capacity calculation by 10%.
  • Heavy Shading: Reduce your capacity calculation by 10%.
  • Kitchen Installation: The A/C’s capacity should be 4,000 BTU higher.
  • Rooms Used by >2 People: +600 BTU for each additional person.

Manual J Calculation

A professional measurement is the most precise. Whether you work with an HVAC company or energy auditor, a Manual J calculation for you home determines the exact HVAC unit size it needs. It takes square footage into account, among many other factors, such as climate zone, ductwork design and condition, and the number and style of windows in your home. Insulation, shade or sunlight, presence of heat-generating appliances, and the number of people using the space in question are considered as well. All these details are inputted to determine the exact BTU heating and cooling capacity needed.

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Does Optimal Size Guarantee Efficiency?

There are more considerations than size when it comes to efficiency. One is the type of air conditioner; window units, for example, sit low, while a wall-mounted unit delivers cool air from a higher point. This cools a room more thoroughly. A system’s energy-efficiency ratio (EER) counts as well; and always look for the ENERGY STAR label. Cleaning your filters, setting an optimal temperature, and using timers for cooling when it’s most needed also help improve efficiency.

Let Us Help Choose the Right AC for You

The professional technicians at Sky Heating & Air Conditioning can make all the calculations and recommend the best air conditioner for you. Our high-quality services are depended upon throughout Portland and The Dalles, OR. Call 503-235-9083 or contact us online to request a consultation.

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How do I know what size heating and air conditioner I need? ›

To calculate the size of the air conditioner you need for a room, first, multiply the length of the room with its width. Then multiply it with 25 BTU to get the ample cooling for the room under different weather conditions. For example, if the room is 15 feet long and 12 feet wide, it comes to 180 square feet.

How many square feet does a 3 ton AC unit cover? ›

3-ton is equal to 36,000 BTU. If you apply the 20 BTU per sq ft rule of thumb, you can see that a 3-ton air conditioner cools about 1,800 square feet spaces.

How do I choose the right size air conditioner for my home? ›

As a general rule, an air conditioner needs 20 Btu for each square foot of living space. But other considerations, such as the ceiling height and the size of your windows and doorways, might call for more cooling power. To measure your room, multiply the length by the width.

How many square feet does a 5 ton AC unit cover? ›

A 5 ton unit will typically cool between 1500 square feet and 1800 square feet. See our free system sizing calculator if you need help. The broad range for sizing is 500-600 square feet of living space per ton of cooling.

How big of an AC unit do I need for 2000 sq ft? ›

2,000 square feet x 20 BTU = 40,000 BTU. Since 1 ton equals 12,000 BTU, you'll divide 40,000 by 12,000 with a math equation that looks like this: 40,000 BTU / 12,000 BTU = 3.33333 tons. Round that up, and you're looking at a 3.5-ton AC unit.

What happens if HVAC is too big? ›

Air conditioners that are too big consume more energy, endure more wear and tear, and simply don't work as well or as long as an appropriately sized unit. This can cause higher utility bills, more repairs, and discomfort in your home.

Is it better to undersize or oversize a furnace? ›

Even a slightly undersized furnace will accomplish the job the majority of the time. Taking things down a few sizes will more than likely solve some of your common heating problems like too high of a utility bill while half of your house is blazing and the other half is an icebox.

What happens if my AC unit is undersized? ›

A properly sized unit will kick on and off periodically to control the temperature. Undersized air conditioners will struggle to ever get the room cool enough and therefore will fail to go through healthy on and off cycles. This extra wear and tear will lessen the life of your ac and cost you more in repairs.

What size heat pump do I need for a 2000 sq ft house? ›

If you Google “heat pump calculator,” you'll probably find a rule of thumb like this: “You need 30 BTUs of heat for every square foot of living space you want to heat or cool.” If you have a 2,000-square-foot home, this rule of thumb suggests you need a 60,000 BTU heat pump.

What size AC unit do I need for a 1500 sq ft house? ›

What size air conditioner do I need for a 1,500 square foot house? A 2.5 ton air conditioner is best because about 30,000 BTU is needed for a house that's 1,500 square feet.

How many square feet will a 2.5 ton AC unit cool? ›

- 1500 sf

What size AC unit do I need for a 2400 sq ft house? ›

The answer to the question, “what size AC unit for 2400 square feet?”, would be, is 60,000 BTUs or 5 Tons. It's possible to fall between unit sizes, so if that's the case with you, then you should choose the next higher size.

Will a bigger AC unit cool my house better? ›

An “oversized” air conditioner will cool your house quicker, but it will use more electricity and will not remove humidity adequately. Contrary to popular belief – and intuition – long AC system run cycles are far more desirable and energy efficient than short-run cycles.

How many square feet will a 4 ton air conditioner cool? ›

A 4 ton unit will typically cool between 2000 square feet and 2400 square feet. See our free system sizing calculator for sizing assistance. Many people will tell you to figure about 500-600 square feet of living space for each ton of cooling.

What is the difference between 14 SEER and 16 SEER? ›

A 16 SEER AC system is approximately 13 to 14 percent more efficient than a 14 SEER unit. While energy pricing across the country fluctuates (and remember this is at maximum efficiency), a 14 percent savings would save you $13 to $14 for every $100 you spend on your energy bill now.

What SEER rating should I buy? ›

For most homeowners, opting for a unit with a SEER between 15 and 18 is a good choice because it's a balance between the money you'll spend for the unit and the amount you'll save on utility costs.

What SEER is best? ›

Generally speaking, the higher the SEER rating, the better the unit's efficiency. These days, new units must have a rating of at least 13 and most have a rating between 13 and 21, though some models may go even higher. Older and lower-end models, on the other hand, can have a lower rating.

Is 2 ton AC enough for 400 sq ft? ›

To avoid calculations, the rule of thumb says a 1 ton AC covers up to 100 square feet, 1.5-ton covers around 180 square feet and a 2 ton AC can cool up to 240 square feet of space.

What are the disadvantages of oversized air conditioner? ›

Too Hot or Too Cold Air

An HVAC system with excess capacity can heat or cool your home faster, but that speed often results in a couple of other issues. First, your home won't benefit from gradual, even heating and cooling. As a result, you could end up with a number of hot or cold spots throughout your home.

Why an oversized air conditioner is a bad idea? ›

The more it happens, the shorter the life of the equipment. When an air conditioner is oversized, it starts up and shuts down a lot more because it runs for only a short time to meet the thermostat setpoint. Then a few minutes later, it comes on again and runs for a short time.

Is it good to oversize an air conditioner? ›

Oversized air conditioners usually short-cycle, meaning they power up and down throughout the day many more times than units that cycle properly. This needlessly uses up energy, resulting in high energy bills for you. Short AC lifespan – An oversized air conditioner is an overworked air conditioner.

What happens if you have too much BTU? ›

A unit with too many BTU's, will cool the room fast, but leave the room humid. Too few BTU's will never cool the room down and the unit will run incessantly.

What happens if HVAC is too small? ›

If your air conditioning system is too small for the space that it is installed in, then it won't have an efficient enough output. This forces the system to operate far longer than it is designed to, to try to keep your home cool.

Are 80 furnaces being phased out? ›

This is a big change coming in residential & light-commercial furnaces. Effective June 1, 2013, federal law requires that minimum furnace efficiency in the Northwest must be 90%. That means that 80 percent of furnaces cannot be installed after that date.

How do I calculate air conditioner size? ›

You will need to find the length and width of each room and multiply them. Then, you have to add the area of each room together for the total. This figure needs to be in square metres.

How do you know if your AC is too small for your house? ›

5 Signs of an Undersized Air Conditioner
  1. Your AC Never Stops Running. ...
  2. Low Airflow. ...
  3. Your Home Is Never Cool Enough. ...
  4. Your Home Has Temperature Inconsistencies Throughout. ...
  5. High Energy Bills.
Nov 9, 2018

How do you know if your AC is too small? ›

The surest sign of an undersized air conditioner is if you struggle to get your home under 79 degrees. AC units used to be designed to take a space from incredibly warm to incredibly cool in one long, continuous cycle.

How many square feet will a 3 ton heat pump cool? ›

While 3-ton heat pumps are not necessarily heavier than smaller-capacity pumps, they will likely cost more to buy and install. A quality 3-ton heat pump can effectively heat or cool an average area of 1,500 square feet but will be too large for smaller spaces.

Do I need a 2 ton or 3 ton heat pump? ›

Square footage

Here are some guidelines to help you determine how many tons you'll need: 500 square feet: 1 ton. 1,000 square feet: 2 tons. 1,500 square feet: 3 tons.

How big of a central air unit do I need for a 1200 square foot house? ›

If you have a 1,200-square-foot home, you'd need a two-ton unit. A 2,400-square-foot home would need a four-ton unit. Again, there are 2.5-ton and 3.5-ton units in case your square footage doesn't work out perfectly for a two- or three-ton unit, for instance.

How much is a new AC unit for a 1500 sq ft house? ›

On average, when looking to replace your HVAC system, the cost for the unit itself will range between $4,850 and $9,400.
HVAC Installation Cost Per Square Foot.
Square FeetAverage Cost
1,000$4,000 - $5,000
1,200$5,000 - $6,000
1,500$6,000 - $7,000
2,000$7,000 - $8,000
2 more rows
Feb 24, 2023

Is Trane or carrier better? ›

There is no difference in terms of basic and mid-level units of both the brands when it comes to deciding the superiority in terms of quality. However, if you are looking forward to buying a top-line model, then you must go with Trane as it has a better warranty on their compressors.

How big of an area will a 2-ton AC cool? ›

For those of you that don't understand the way AC systems work, a 2-ton unit typically provides cooling for about 900-1,400 square feet of space – give or take.

How many tons of cooling do I need for 2000 square feet? ›

For example, when considering what size air conditioner is needed for a 2,000 square foot home, you would likely choose a 3 or 3.5 ton unit, depending on the climate where you live.

How many tons of cooling do I need for a 2000 square foot house? ›

If your home is 2000 square feet, you can calculate your HVAC needs the same as you would for a 1600 square foot home. Assuming one ton of cooling capacity can cool 400 square feet of your home, you'll need about 5.0 tons of air conditioning capacity. Multiply this by 12,000 BTUs, and you'll get 60,000 BTUs.

What is the difference between a 2 ton and 3 ton air conditioner? ›

HVAC experts eventually divided that number by 24 hours and came up with 12,000 BTU/1-ton AC capacity. Using that measurement, a two-ton AC unit will remove 24,000 BTUs, while a three-ton AC unit will remove 36,000 BTUs. Therefore, the more tonnage the AC unit is rated for, the more air it can cool down.

What size air conditioner do I need for 2500 sq ft house? ›

1,500 – 2,000 sq. feet: 30,000 BTUs. 2,000– 2,500 sq. feet: 34,000 BTUs.

How many square feet will a 80000 BTU furnace heat? ›

Furnace and Air Conditioner size for a Detached 2-story House
Detached House square footage *Furnace Output [BTU/hr]
2500 to 3500 sq ftup to 65,000 BTU/hrup to 80,000 BTU/hr
3500 to 4500 sq ftup to 80,000 BTU/hrup to 100,000 BTU/hr
*The above square footages do not include the area of the basement
4 more rows

What size furnace do I need for a 1200 sq ft house? ›

1,200 square foot home would take between 35,000 and 75,000 BTUs. 1,500-square-foot home would take between 45,000 and 90,000 BTUs. 1,800-square-foot home would take between 55,000 and 110,000 BTUs. 2,100-square-foot home would take between 65,000 and 125,000 BTUs.

What size ductwork do I need for a 3 ton unit? ›

Note: A 3 ton AC needs a round return duct with an 18” diameter. That size duct is 254 square inches, right in line with the calculation for rectangular ducts.

How many square feet is a 4 ton AC unit? ›

A 4 ton unit will typically cool between 2000 square feet and 2400 square feet. See our free system sizing calculator for sizing assistance. Many people will tell you to figure about 500-600 square feet of living space for each ton of cooling.

Is it better to oversize or undersize a furnace? ›

Even a slightly undersized furnace will accomplish the job the majority of the time. Taking things down a few sizes will more than likely solve some of your common heating problems like too high of a utility bill while half of your house is blazing and the other half is an icebox.

How big of a house will a 100000 BTU furnace heat? ›

Determining the Square Footage

In colder climates, you'll want a furnace that generates 40 to 45 BTUs per square foot. At this amount, you'll need 100,000-112,500 BTU furnace to heat a home of 2,500 square feet.

Is a 2 stage furnace worth the extra cost? ›

Should I Buy a Two-Stage Furnace? You are most likely to benefit from owning a two-stage furnace if you own a two or multi-story home in which you intend to spend the next several years or more. Otherwise, you won't get to reap the long-term benefits of lower energy bills.

How much does it cost to install central air and heat in a 1200 sq ft house? ›

HVAC Installation Cost Per Square Foot
Square FeetAverage Cost
1,000$4,000 - $5,000
1,200$5,000 - $6,000
1,500$6,000 - $7,000
2,000$7,000 - $8,000
2 more rows
Feb 24, 2023

What happens if a furnace is undersized? ›

Undersized Furnace

Buying a furnace that is too small for your house can lead to poor heating, which in turn will cause you to use more energy. This wastes money and causes your monthly bills to go up. Furnaces that are too small don't run enough to keep your house warm at a comfortable level.

How do I know if my furnace is too big for my house? ›

Temperature Imbalances

A furnace that's too big for your home can cause temperature inconsistencies. Even large furnaces may struggle with keeping the desired temperature in your home. You will notice that some rooms aren't as warmer as the other rooms.

What happens if ductwork is oversized? ›

Oversized ductwork means that your HVAC equipment is going to have to push air that much harder to make it through your ducts. This means cold winters and hot summers as well as a higher risk of damage to your AC and heating systems.

What happens if ductwork is undersized? ›

Having undersized ducts is disastrous for air circulation since it restricts airflow, causing the HVAC unit to strain. Consequently, more energy is used up in operation, ultimately causing a rise in the energy bill. Furthermore, this leads to a reduced system lifespan.

Can air ducts be too big? ›

Oversized ducts could cause your HVAC system to work too hard and limit the amount of conditioned air that reaches your home. Forcing your system to work harder than it should leaves it prone to breakdowns and increases your energy usage.

How big of a house will a 4 ton AC unit cool? ›

Choose a unit that is 3.5 tons if your home measures more than 1,800 but not more than 2,100 square feet. A four-ton unit is suitable for homes that are more than 2,100 square feet up to 2,400 SF.

How big of an AC unit do I need for a 1500 sq ft house? ›

A 2.5 ton air conditioner is best because about 30,000 BTU is needed for a house that's 1,500 square feet.

How big of an AC unit do I need for a 2500 square foot house? ›

Step 5: Match your square footage to an HVAC size chart
Home Square FootageAir Conditioner Size (Tons)
1,000-1,500 square feet2 tons
1,500-2,000 square feet3 tons
2,000-2,500 square feet4 tons
2,500-3,300 square feet5 tons
1 more row


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