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December 01, 2022

How to Calculate What Size of HVAC Unit You Need

HVAC Unit - LG Home Comfort

When it comes to household appliances, size does matter. Knowing what size you need is essential if you want to purchase an HVAC unit for your home. An improperly sized unit can be ineffective, increase energy costs, and cause wear and tear on the system. So, how do you calculate the size of the right HVAC unit for your home? Read on to find out.

How to Calculate Air Conditioner Size for a House?

Sizing the AC unit for a house is essential to ensure the indoor unit is large enough to cool the space properly but not so oversized that it wastes energy. In terms of cooling capacity, the capacity of a window air conditioner typically ranges from 5,000 to 12,500 British thermal units (Btu/hr.). On average, an air conditioner needs 20 British thermal units per square foot.

However, other factors, such as the height of your ceiling and the size of your windows and doorways, might require more cooling power.

In order to measure your room, multiply its length by its width. If there are no doors between rooms, you will need to add the size of both rooms together so that the particular air conditioner can cool both spaces. Energy Star suggests that you make changes according to the circumstances as follows:

  • Consider reducing the capacity by 10 percent if the room is heavily shaded.
  • Increase capacity by 10% if the room is very sunny.
  • For each additional person in the room, add 600 Btu.
  • If the central air units are located in the kitchen, increase capacity by 4,000 Btu.

Room Air Conditioner Sizing

Minimizing your electricity bill requires choosing the right air conditioner for a given room size. Air conditioners with small capacities will have a difficult time cooling large rooms, or they might not be able to do so at all. On the other hand, if you choose an air conditioner that is large for your room, the room will be cooled very quickly but will not be dehumidified. As a result, the room becomes cold and clammy, which is uncomfortable. Therefore, you should determine what size air conditioner you need before purchasing one.

You can find your room’s covered area by measuring the width and length of your room with any measuring tools you have at home. To get the area of your room, enter these values into the air conditioner size calculator you can find online. In addition, you can also use a free online square footage calculator to determine the area of an irregularly shaped room by selecting the multiple rooms option.

If you already know the size of your room, use the chart below to find out what size of an air conditioner you should buy:

Area to be cooled (sq ft) 

Capacity needed (BTU/hr)







350 to 450


450 to 550


550 to 700


700 to 1,000


1,000 to 1,300


1,300 to 1,500


Sizing Air Conditioners: How Is It Done?

There often needs to be more clarity among homeowners regarding how to size an air conditioner.

Properly sizing an air conditioner is based on its cooling capacity, measured in BTU (British Thermal Unit). Whether you choose a window air conditioning unit or a central air unit, both can provide you with excellent energy efficiency. This will result in lower operating costs depending on the area to be cooled.

While many believe room air conditioner sizing is determined by its dimensions, this is not true. If you want to determine the right size air conditioner you need, you must first calculate the total square footage of the area served by the air conditioner.

To calculate the correct ac size, multiply the room’s length (l) by its width (w).

Then, even if the rule of thumb for sizing AC units is 20 BTUs for every sq ft of living space occupied, multiply the total square footage of your living space by 25 to determine the number of BTUs needed. This number is a safe estimate that accounts for various daily weather conditions, such as rain and humidity.

For example, your room is 20 ft long and 14 ft wide.

  • 20 (l) x 14 (w) =280 square feet.

Then, multiply 280 square feet by 25 BTU to get the minimum BTU air conditioner required.

  • 280 sq. ft. x 25 BTU = 7,000 BTU

An AC unit with a 7,000 BTU cooling capacity is needed.

What Size of AC Do You Need?

Many people’s thoughts turn to air conditioners when the weather begins to heat up. But how can you determine your home’s AC capacity and size? It can be confusing, but do not worry; we can help. We will walk you through the factors you must consider when choosing an AC unit.

Step 1: Determine the proper type of air conditioner needed.

There are three main types of AC systems, all of which cool in a very similar way. Most homes have ductless AC systems, packaged air conditioners, or split-system air conditioners. It is essential to ensure you have the right unit type before determining its size. If you are still deciding which system is best for your space, consult an HVAC contractor to help point you toward the best option.

Step 2: Research HVAC sizes based on ratings.

In order to choose the best model of AC for your home, research the ratings of the style you like. Air conditioners are generally rated according to their energy efficiency and cooling capacity.

When trying to determine the size of AC to get, it is crucial to understand how those two components are represented. The efficiency of energy is measured by the Seasonal Energy Efficiency Ratio (SEER), while its cooling capability is denoted by its tonnage rating. The higher a system’s SEER and tonnage rating typically mean more efficient cooling capabilities and lower energy bills.

Step 3: Determine the right size AC for your home.

Now that you know the correct type of AC system for your home and which ones have good reviews, it is time to get a size estimate of the air conditioner you need. The most crucial factor here is square footage – this tells us how big or small an area needs to be cooled for an effective air conditioning system. You can use an online calculator or measure each room individually (including closet space) to estimate square footage accurately.

Step 4: Request an energy audit.

The final step in choosing the right size AC unit is requesting an energy audit from a reliable HVAC technician or contractor. An energy audit considers factors like insulation levels, amount of sunlight exposure in certain rooms, windows sizes/types, and more., which can all impact cooling performance in addition to square footage measurements alone. An experienced technician should be able to provide valuable insight into how much cooling power is needed based on all these factors combined.

Final Thoughts

Choosing the right-size AC unit can be simple. It takes just a few calculations based on your home’s square footage and cooling load to determine which system best fits your needs.

Understanding how big of an air conditioner is required for each space in your house based on its unique characteristics—insulation levels, sun exposure, and more.—you can ensure that you get an appropriately sized system that will efficiently cool down each room while saving money on energy bills.

With this knowledge at hand, now all you need to do is pick out an AC unit that best fits within both your budget and requirements.

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