How to Calculate HVAC Tonnage

When installing a heating and cooling system into a location, it is imperative to first determine the heating and cooling needs of the location. The needs will determine the HVAC system needed in the room. HVAC stands for heating, ventilating, and air conditioning, all of which are part of the building design for mid size buildings and larger. The following will walk through calculating the heating and cooling thermal units (BTU) and how to convert that number into tons.

Difficulty: Moderate

Instructions

Things You'll Need:

• Measuring Tape (metric)
• Wattage labels for all equipment at the location
• Wattage labels for all lighting
• Calculator

1. Measure the area of the room and convert that figure into BTU's. The area of the room is determined by multiplying the length and width. The measurement must be in meters, (1 foot equals .3048 meters). Multiply the area by 337 to figure out the area BTU.
   
   Room BTU = Length x Width x 337

2. If there are north or south-facing windows in the location, calculate the BTU for each window by measuring the area of each. For north-facing windows, multiply the area by 165. For south-facing windows, multiply the area by 870. If you live in the Southern Hemisphere, reverse the calculations (165 for south, 870 for north)

3. Calculate the BTU of the number of people who use the location. Multiply the occupants by 400 for the BTU.

4. Any equipment in the room needs to be measured for their BTU output. To determine the output, multiply the total wattage for the equipment by 3.5.

5. Determine the lighting BTU by multiplying total wattage for the lighting by 4.25.

6. Add the figures from steps one through five. The result is your total heat load. Multiply this number by two to determine the amount of cooling required.

7. Convert your heating and cooling load to tons by dividing the BTUs by 12,000. The resulting figure is the HVAC tonnage.