Step 1
Read the elevator equipment manual and see if the system requires a specifically sized AC unit. Most manuals will not have a specific size of AC required, just the temperature range in which the equipment can properly operate. If your manual does not indicate AC size, then you must size it manually.
Step 2
Find the square footage for the elevator machine room, using the tape measure to measure the width and length of the room. Multiply the width and length to obtain the square footage of the room: A room 10 feet wide and 12 feet long would be 120 square feet.
Step 3
Go to the Energy Star (energystar.gov) website to find a chart that indicates capacity needed per square footage. Use the chart to find the British thermal units (BTUs) required for the amount of square footage of the room.
Step 4
Add 4,000 BTU's to the amount indicated on the chart based on square footage. For this example, a 120-square-foot room needs a 5,000 BTU air conditioner, according to the chart. Add 4,000 to the 5,000 indicated on the chart to compensate for the mechanical heat created by the motors to give you a total of 9,000 BTU of cooling capacity.