The glass block glazing unit (GBGU) test sample (PCC) for the U-factor test was created by installing nine blocks into a surround panel measuring 81.28 cm (32 in.) by 81.28 cm (32 in.) and weighing 32.6 kg (75 lbs).
This value was used for the SHGC testing for the glazed area of each GBGU to account for any heat loss or heat gain due to any temperature differential from the inside air to the outside air through the vision area of the GBGU.
There were a number of difficulties that had to be addressed during the testing of GBGUs. One difficulty was the weight of the GBGUs, which made them difficult to mount and support in the calorimeter.