Sizing a Large Portable Air Conditioner

Choosing the proper large portable air conditioner is essential for successful cooling. Portable coolers that are too small cannot keep up with cooling demands. On the other hand, units that are too large cool the temperature down so fast that the thermostat will cycle off before the space has a chance to be dehumidified and properly controlled. Over sizing is a common problem, as bigger is not always better. However, the experts at Mobile Air are here to help find that perfect portable air conditioner for your application.

The cooling capacity of an air conditioner is rated in BTU’s (British thermal unit) per hour or tons. In air conditioning, tons refer to the cooling capacity of the unit, not the weight. There are three primary methods for properly sizing a space for portable air conditioning:

Large portable air conditioners are often used in unexpected, unplanned or emergency air conditioning situations. Through our practical experience, Mobile Air has developed a few rules of thumb for accurately and quickly determining a client's large portable air conditioning needs.

1. Classic Rule of Thumb

  • Server / Computer Room: 1 Ton per 200 to 400 sq.ft..
  • General Office Areas: 1 Ton per 400 sq. ft..
  • Hospital General Areas / Labs: 1 Ton per 400 sq. ft..
  • Hospital MRI Imaging: 1 Ton per 250 sq.ft..
  • High Heat Industrial Plant: 1 Ton per 200 sq. ft..
  • Outdoor Tent (summer time): 1 Ton per 200 sq. ft..

2. Replace Ton for Ton:

“Ton for Ton” is the second sizing method. This method is used when the permanent system is being replaced, repaired, or otherwise unavailable. In this situation you would use a portable air conditioning unit of equal cooling capacity to that of the permanent system. For example, if your permanent system has a capacity of 10 tons, then looking at a 10 ton portable cooling unit would be a good place to start.

3. Heat Load Calculation

Using the “Heat Load Calculation” method requires a Mobile Air representative to complete a survey of the cooling area in your facility to determine the proper cooling capacity for your application. Some of the factors used in heat load calculation are:

  • The physical size of the space to be cooled including the ceiling height and the shape or lay-out of the space.
  • The climate zone of the location being cooled.
  • Insulation values of the structure.
  • The number, size, and location of windows/skylights.
  • Survey of heat generating items: lighting, computers, printers, kitchens, number of people, processes etc.
  • Outside air requirements entering the building.


For questions about large portable air conditioner sizing, please feel free to contact us. We are happy to help you properly size your portable air conditioning rental.

Contact Us