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What Size AC Do I Need?

Figuring out what size air conditioning unit you need is as simple as taking a tape measure and looking at the length, width and height of your living space. You could also call in a professional to help you find the air conditioner you need to cool off the room. Use these calculations to choose the right size for your AC system.

1. Square Footage AC Calculator

To figure out the square feet within your room, measure the length and width of the room. Use these tips to calculate the area of your living space:

  • In rectangular and square areas, multiply the full width by the length.
  • In triangular places, use the same formula but cut it in half.
  • If you have an abnormal room shape, divide the room into rectangles, triangles and squares and use the previous equations. Add the total square footage of all the various dimensions.

2. AC BTU Calculator Chart

How many BTUs do you need? After you’ve measured the dimensions of each room in the home where you want to put an air conditioner, you can figure out what you need based on the BTU conversion chart.

Find your room’s square footage on the left column, and then use the right column to get the proper capacity for the AC unit. The cooling capacity is measured in BTU per square foot. A 3-ton AC unit can cool a small house, while a 5-ton AC unit can cool a bigger home.

3. Make Adjustments as Needed

While this process seems pretty straightforward, you also need to make some adjustments based on these factors:

  • Decrease the cooling capacity of the unit by 10% if the area has shade.
  • Increase the cooling capability by 10% if the area is in direct sunlight.
  • Increase the total by 600 BTUs for every extra person in a room if the room is occupied by more than two people regularly.
  • Increase capacity by 4,000 BTUs if the air conditioner is in the kitchen.

4. Heat Zone HVAC Calculator

Throughout the world, various climate zones indicate the heat that each region experiences. Contractors and builders use climate zones to get the most energy savings in a home. Here are the heat zones in the United States to determine which one you live in and how it affects the size of your AC unit:

  • Hot-humid: You are in a hot-humid climate if you live in the southeastern part of the United States.
  • Mixed-humid: This climate consists of the central-eastern region of the country.
  • Hot-dry or mixed-dry: You may feel hot and dry air if you live in the southwestern part of the United States. The difference between hot-dry and mixed-dry is that mixed-dry sees less warm temperatures throughout the year.
  • Cold or very cold: In the northern part of the country, you get colder days more frequently.
  • Marine: On the west coast, the weather is pretty consistent, but you’ll see rain each month.

These climates got their names based on the amount of precipitation and the frequency of warmer temperatures compared to the rest of the country. You could figure out what type of air conditioning system you need depending on how often you have sunny days in your region. A house in a hot-humid climate would need a more powerful AC unit than one in a cold part of the country.

5. Bring in a Professional

A professional HVAC contractor will know how to size your cooling system for your living space. They can give you an in-house estimate and explain how much it would cost to install an AC unit that would work best for your living conditions.

If you’re checking out our products, you could contact an expert from MRCOOL. We offer free lifetime tech support on all of our merchandise, so if you’re ever stuck, just give us a call. After years of experience, we know where our products fit best, especially our DIY® Multi-Zone, which can cool the whole house.

Why Does the Right Size Air Conditioner Matter?

If you order the wrong size AC unit, you could end up spending more money than necessary to cool your home. Here are some of the reasons why you shouldn’t install a cooling system that’s much too big or far too small.

1. How Do I Know If My AC Unit Is Too Big?

While homeowners tend to believe that a bigger cooling system is better, that doesn’t always apply. A 4-ton AC unit in a tiny space could reduce the air quality of your home without providing additional benefit.

Here are some of the reasons why a large AC unit may be hurting your home:

  • An uncomfortable room: The HVAC system cools the air in your home and the compressor takes out the moisture from the atmosphere. When the AC is too big for the room, it’ll turn off faster than usual, so the compressor won’t have time to remove all the humidity. As a result, you’ll have a sticky, stuffy room instead of a comfortable atmosphere.
  • Dust mites and mold: When the room has too much humidity in it, the result is mold and mildew. You may also see many more dust mites throughout your living space, along with all that moisture in the air.
  • A loud air conditioner: A cooling system has shorter cycles if it’s too big for the room. To find out if it’s too big, time a sequence on a hot day, and if the system only cycles for a few minutes, it’s too big. You can also tell by the sound. If the AC unit sounds like a freight train, it’s too big for the living space. A properly-sized air conditioner makes very little noise, if it makes any noise at all.
  • Higher energy bills: A large air conditioner will cost more money upfront, including the price of installation, because of its size. It can also increase your energy bills. Since an oversized AC unit starts and repeatedly stops to cool down the house, it’ll spend more energy, and your energy bills will increase over time.
  • Signs of wear and tear: An oversized cooling system starts and stops periodically throughout the day, so the compressor will take more of a hit than ones that are the right size. The more wear and tear on your AC unit, the more you’ll have to pay in repair costs.
  • Structural damage: You might see structural damage in the drywall or wood products you may have, especially if your home is in a humid climate. A massive cooling system won’t remove enough moisture from the air, so it can damage these areas of your home that aren’t resistant to moisture.

2. How Do I Know If My AC Unit Is Too Small?

Like having a unit that’s too big, you don’t want one that’s too small, either. Here are some of the reasons why a small room air conditioner may be costing you money:

  • Your AC never stops running: The air conditioner absorbs warm air and moisture inside the home and cools it until the air reaches the number on your thermostat. If the AC is too small for the house, it’ll keep trying to reach the temperature, but it won’t ever have the capacity to cool the whole space. Once the thermostat reaches the proper temperature, the unit should turn off, but since it never reaches the thermostat level, it keeps running.
  • Low airflow: If you keep up with the cleaning of your air filters and there still isn’t a lot of air coming out of the unit, the AC unit might be too small for the house. Since the AC is supposed to reduce the humidity in your home, you may also experience humid air throughout the house if it’s the wrong size.
  • Your home is never cold enough: Your AC unit could fail for several reasons, including dirty air filters and a clogged condenser unit. If your AC is clean, your house should be a comfortable temperature, but if you don’t have adequate size, the air will be warm and stuffy.
  • Your home has inconsistent hot or cold spots: Walk through your house and feel the temperature of each room. Keep in mind that the kitchen, living room or bathroom might be a different temperature and humidity if you’re cooking or someone is taking a shower. Baths and cooking appliances make heat, so they’ll affect the atmosphere of your living space. Otherwise, if one area of the home is much warmer or colder than the rest, then your AC unit isn’t powerful enough to reach the whole house.
  • High energy bills: If the cooling system never shuts off, it’ll use more energy to run each month. Since a small AC unit will never complete a cooling cycle, it will have to crank out air and start all over again each time. You will see a rise in your energy bills as your unit struggles to keep up with the heat in your ample space.