Fig. 2 illustrates a GFX cross-section and nominal operating water temperatures of a Model G3-60 (or S4-60) for incoming water temperatures found in three U.S. Climate Zones.
NOTES: In order to match the energy savings of a $530, 60-inch Model G3-60 GFX, a $920, 78-inch long Model R3-78 Power-Pipe is required. A slightly less efficient, 72-inch Model R3-72 Power Pipe is also sold by Home Depot for $914.40.* [See performance comparisons based on equations @ http://www.gfxtechnology.com/EFF.pdf (pg. 3.)]
For installations with height restrictions, a 30-inch long, $350 Model G3-30 GFX can be used. It offers 41% efficiency; about 6% more than a 30-inch Model R3-30 Power-Pipe that's rated @ 34.8%** and costs $560.
* Prices in October of 2016
** Tested according to CSA B55.1; the Canadian version of U.S. DOE standards Virginia Power used to test GFX over 20 years ago.