Im currently replacing an air conditioning unit in a commercial area which has a front and back door which are used for customers to enter and exit. The area is 20 foot wide by 65 foot in length and the ceiling is 9 foot. The building is located in central Illinois. The typical time for each customer to remain in the building is 1 to 3 hours.

Any information on the proper ton unit for this area would be helpful.

Thanks for any assistance on this issue.

How much lighting? How many computers and monitors? LCD or CRT monitors? What type, size and direction of windows? How many patrons at a time? Split system or rooftop? Is the return air just pulled through egg crates in a drop ceiling?

You really need to preform a manual J calculation to determine the heat load.

If you have lots of customers entering or leaving consider a double-door entry way. Other solutions are a special blower mounted above the door which keeps the outside air from entering the heated space.

There are just too many variables besides cubic feet and number of occupants. Heat gain from other devices, windows, and heat loss by the structure play a part as well as climate.