Selection Criteria for Coil Heaters;

The flow rate through the heater coil is just as critical as the flow rate through the cooling coil. Because the temperature of the water circulating through the coil is significantly higher than the temperature of the air leaving the coil, the coil’s surface area—and consequently the number of coil rows—results in a much lower pressure drop on the air side of the coil compared to a cooling coil. It is recommended that the air velocity in heater coils not exceed 3 m/s.
The dry-bulb temperature of the air entering and exiting the coil...

The dry-bulb temperature of the air entering and exiting the coil must be determined.
The type and flow rate of the heating fluid circulating in the heating coil must be determined.