Six Rivers Solar Heat Exchange Storage Tanks. Designed by engineers with 21 years of solar installation and solar servicing experience, these tanks and systems were tested and refined in real world applications for more than 10 years. These ruggedly designed tanks form the core of our modern “Drainback” solar water systems and will provide decades of dependable service. With a variety of standard sizes and the capability to construct custom tanks, these components make ideal replacement tanks for older systems [see below] or original equipment for new systems as shown above. Use the 120-gallon model for most typical homes, the larger models for large homes and commercial/institutional use as well as integral radiant floor heating systems. Super highquality tanks backed up with a limited 20-year warranty.