Both will do the job of heating the water. Two of the major differences: 1.) FAFCO panels need to have hold-down straps across the whole array. That means more penetrations throught the roof. Heliocol does not need these on most installations. 2.) FAFCO panels (as do most all other brands) use reinforced rubber tubes with hose clamps to connect the panels. Heliocol uses an "O" ring and clamp design. The FAFCO panels need to have the hose clamps tightened regularly, usually every other year or so. This always results in the headers being deformed (crushed) over time, leaking at the header, and having to be replaced.