June 20, 2021


When buying a commercial air conditioning unit, most people focus more on the acquisition and installation costs. Some business owners make the mistake of purchasing the air conditioner based on cost considerations alone. You should, however, consider the cooling load per square foot, and the cooling capacity.

While you might feel tempted to go for the cheapest system available, an undersized AC unit will not achieve optimal cooling capabilities in a commercial setting. It will also work harder and run for long hours to meet the cooling demands, which leads to high utility bills.

On the other hand, a bigger air conditioner than required will cost you too much upfront. It will also cycle on and off very often, which strains the system and lowers its expected lifespan. The short cycles leave behind excess humidity, too. Here are various steps to calculate the right-size AC unit for your commercial building and optimize your cooling load per square foot.

1. Calculate the square footage of the building you intend to cool

Start by measuring the square footage of all the rooms in the building. If you have a multidimensional structure, divide it into various sections to accurately calculate the area. For a rectangular space, you’ll multiply the length and width. If you have some triangular rooms, multiply the length and width and divide the answer by two. For circular spaces, get the distance from one end to the center and calculate the area.

If there are rooms that open up to one another, air circulates freely in such space, and you need to treat them as a single room while calculating the area. Add the answers to get the total square footage of the building your AC unit needs to cool. Exclude areas that you don’t want to cool, like the garage. Keep in mind that the bigger the building in terms of square footage, the more powerful the air conditioner you’ll need.

2. Determining the required BTUs

The British thermal unit measures how much energy your AC unit will require to pull out hot air from the building and recirculate back cool air. Generally, BTUs tell how strong a unit is. Keep in mind that a commercial air conditioner will require around 1,200 BTUs to cool a 500-square-foot space in an hour.

So, divide your building’s total footage by 500, and then multiply the answer by 1,200 to determine the required BTUs. For example, if you have a structure of about 10,000 square feet, you’ll divide this by 500 to get 20. Multiply 20 by 1,200, and you’ll find that you need a unit with 24,000 BTUs to cool the space adequately. You can buy an air conditioner close to the BTUs calculated, but there are still some considerations that you need to make.

3. Consider insulation of the building

The manual J scientific method of determining the right-sized air conditioner works well for large buildings. Based on this method, you should consider the building insulation, materials, and wall thickness to choose the right AC unit size.

A well-insulated building will hold the conditions air better, so you can use a slightly less powerful air conditioning system. However, a poorly insulated building may absorb heat, warming up the air in the building. The poorly insulated building also allows the conditioned air to seep out. As a result, the AC unit will require more cooling power to maintain desirable indoor temperatures.

Thick walls prevent heat from entering the building. Keep in mind that although large windows give commercial spaces better lighting and a spacious feel, they allow entry of solar heat, which adds to the volume of air that the AC unit needs to cool.

Modern buildings also have better insulation than older ones since most states currently regulate the level of insulation required for commercial spaces. For each poorly insulated window in a building, add 100 BTUs to account for solar heat loss.

4. Adjust the BTUs based on the ceiling height

Note that the square footage calculation works on the assumption that the rooms in the buildings have 8-foot ceilings. If the rooms have ceiling heights higher than 8 feet, this can affect your AC unit’s efficiency. Add around 10% to your calculated BTUs per foot of ceiling height beyond 8 feet.

5. Consider the number of people occupying the building

The human body naturally dissipates heat. This increases the volume of air that an air conditioner needs to cool. As a rule of thumb, you should add about 380 BTUs for each person who occupies space within the building the entire day. If you can’t ascertain the exact number of people in a room or the number varies, use the average daily occupancy rate. For instance, if 200 people are occupying the building daily, you would add 76,000 BTUs to your initial calculation.

6. Don’t ignore the design and applications of the building

You shouldn’t overlook the building design and the type of rooms you intend to cool. If you want to cool a multistory house, the upper floor acts as insulation for the spaces below. You’ll therefore need more BTUs to cool the upper floor and less to cool the ground floor. A multistory building will require less cooling capacity than a ranch-style building.

If you have some west or east-facing rooms, they tend to get hot during the summer, so you need to account for this while calculating the BTUs required. Consider the commercial building space applications, whether it’s a restaurant, a grocery store, a retail outlet, or an office space. Keep in mind that heat-dissipating appliances will make your air conditioning system work harder. Hence, add 1,200 BTUs for each kitchen space within your building. If your commercial building has a gym, you’ll need more power to cool it. Add around 380 BTUs for each person exercising at a particular period.

7. Consider the outdoor climate

Account for the difference between the outdoor temperature and your desired indoor temperature range. If the commercial building is in an extremely hot region, you’ll need a more powerful AC unit to maintain the desired temperature. Those in colder areas can go for a less powerful unit within the calculated range.

Are you looking for professional AC sizing services?

A commercial AC unit is a substantial investment, so you want to ensure that it lasts for its expected lifespan. If you install the right-sized unit, it runs smoothly, limiting the chances of frequent breakdowns or quick and constant wear. Determining the right AC size for a large building can be a complex task, and it’s a good idea that you seek professional assistance. An experienced technician has the proper knowledge and tools to accurately measure the cooling needs in the building and recommend the correct AC power level. They’ll also check the ductwork compatibility with your system before installation to maintain high efficiency.

If you need professional help determining the right AC unit size for your commercial space, reach out to Beyer Mechanical. We provide commercial AC and heating systems installation, repair, and maintenance services. Our company also offers professional HVAC construction services along the I-35 corridor in New Braunfels, Schertz, Austin, Pleasanton, and Corpus. Give us a call today to try out our services.

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