Annular Space 1 Hole Diameter Inches Centimeters 2 O/S Casing Diameter Inches Centimeters For GEOTHERMAL LOOPS use the following as casing diameters: 3/4" Loop = 1.5" 1" Loop = 2.0" 1-1/4 "Loop = 2.3" 3 Depth of Hole Feet Meters