Solar Thermal Pipe & Fittings
Pre-insulated twin stainless steel solar thermal pipe systems, brass compression fittings and installation accessories — everything needed for a professional solar collector to hot water cylinder installation. All products in this range are part of the K-FLEX Twin Solar system, engineered in Italy for fast, reliable solar thermal pipework.
Unlike traditional copper solar pipe, K-FLEX Twin Solar uses flexible corrugated stainless steel tubes pre-insulated with K-FLEX® SOLAR HT high-temperature elastomeric foam and enclosed in a UV-resistant outer sheath. The result is a system that installs faster, performs better over long pipe runs, and withstands the outdoor conditions typical of UK solar thermal installations.
Twin Solar Pipe
Available in two insulation thicknesses to suit different installation requirements:
- K-FLEX Twin Solar System – 14mm Insulation — suitable for standard domestic installations with shorter, protected pipe runs. Available in DN16, DN20 and DN25, in 10m to 25m coils.
- K-FLEX Twin Solar System – 20mm Insulation — recommended for longer runs, exposed rooftop locations or unheated roof spaces where maximum thermal efficiency is required.
Solar Thermal Fittings
The complete range of K-FLEX Twin Solar brass fittings for every connection point in the system:
- Compression Couplings — external and internal thread, DN16 to DN25, tool-free assembly
- Straight Fittings — Ø18mm and Ø22mm, DN16 to DN25
- Double Couplings — for joining or extending pipe runs
- Olives — replacement compression olives, DN16 to DN25
- Copper Connection Sets — stainless to copper transition in 15mm and 18/22mm
Accessories
The K-FLEX Twin Solar Accessories range includes flange tools, tube clamps, nipples, nuts, split rings, gaskets and oval pipe supports — everything required for a complete professional installation.
Frequently Asked Questions
What is Twin Solar pipe?
Twin Solar pipe is a pre-insulated solar thermal pipe system consisting of two corrugated stainless steel tubes enclosed within a single insulated outer sheath. It is designed to connect solar thermal collectors to hot water cylinders, carrying glycol/water heat transfer fluid between the two. The twin configuration means both flow and return pipes are contained in one flexible assembly, simplifying installation significantly compared to running two separate copper pipes.
DN16 vs DN20 — which size do I need?
DN16 is the standard size for most domestic solar thermal installations with one or two collector panels. DN20 is suited to larger domestic systems or commercial installations with higher flow rates and more collector area. DN25 is used in high-capacity commercial systems. If in doubt, check your solar controller or collector manufacturer's flow rate specifications.
What insulation thickness should I choose — 14mm or 20mm?
14mm insulation is suitable for most standard domestic installations where the pipe run is relatively short and partially protected. 20mm insulation is recommended for longer exposed runs, unheated loft spaces, or where the pipe is routed externally for any significant distance. The thicker insulation reduces standing heat loss and improves overall system efficiency.
Can corrugated stainless solar pipe be buried or concealed?
K-FLEX Twin Solar pipe is designed for above-ground solar thermal installations. For buried or concealed applications, consult the K-FLEX technical datasheet and ensure appropriate additional protection is in place. The UV-resistant outer sheath is rated for outdoor and rooftop exposure.
Is K-FLEX Twin Solar compatible with glycol solar fluid?
Yes. All K-FLEX Twin Solar pipe and fittings are compatible with glycol/water heat transfer fluid as used in closed-loop solar thermal systems.