The first step in replacing your HVAC system's coils is precise measurement of the existing coils. A coil measuring tool can be used to obtain the diameter, or you can use a tape measure. Typical tube diameters are 0.375, 0.5, 0.625 or 1".

Counting the number of rows and fins on your unit is also desired. Chilled water and direct expansion coils have anywhere from one to 10 rows, while condenser coils can have anywhere from one to six rows. Steam or hot water coils usually have two rows. Count the number of fins per inch using either a coil measuring tool or tape measure.

The heigth and length of the fins must also be measured.The envelope dimension of the coil, the coil length (including manifolds and bends), and the connection sizes wil also help you determine just which high-quality coils you need for your HVAC system.