1. Look at the manufacturer's label. The manufacturer's label will typically be located on the side of the air handler. It will list the model number, serial number, and tonnage of the air handler.
2. Measure the airflow. The airflow of an air handler is measured in cubic feet per minute (CFM). The CFM rating of an air handler is typically listed in the manufacturer's specifications. To measure the airflow, you will need a flow meter.
3. Calculate the heat load. The heat load of a space is the amount of heat that needs to be removed from the space in order to maintain a comfortable temperature. The heat load of a space is measured in British thermal units per hour (BTUH). To calculate the heat load of a space, you will need to know the square footage of the space, the insulation level of the space, and the desired temperature of the space.
Once you have determined the tonnage of your indoor air handler, you can select the appropriate outdoor unit. The outdoor unit must be matched to the indoor air handler in order to work properly.
