What tubing should I use for my radiant panel?

• Regarding heat transfer, plastic and rubber materials are insulators where as copper is not. This can be tested by running the same temperature water – let’s say 110 degrees F - through each piping material. If you were to place your hand on each tube, you will find the copper tubing much warmer than the others since it allows the transfer of more energy from the water through the tubing walls.
• Copper’s ability to handle pressure allows it to be used in both high and low pressure applications while meeting all the testing requirements of the Universal Plumbing and Mechanical Codes. Type “L” copper tubing is rated at over four times the bursting strength of the strongest plastic tubing. Plastic (PEX) and rubber tubings are rated at a maximum of 100 psi and in some cases only recommended to be tested at 30-60 psi prior to being covered with concrete.
• Copper wins in the temperature rating as well. There is no concern about damage occurring over the years from repetitive expansion and contraction caused by the hot water medium. There have been cases where the heat from the water has molecularly deteriorated the plastics and rubber tubing causing brittleness and subsequent failure and leakage in the systems. This is a characteristic never seen in copper tubing. Beyond normal operation, system operating temperatures have sometimes increased beyond performance limitations due to malfunctioning boiler equipment and led to additional failures of the plastic and rubber tubings. The temperature limitations of copper far exceed the heating abilities of the boiler equipment and therefore could not be damaged by any unusual boiler malfunction.
• System design is most efficient with copper tubing because joints can be welded and manifolded in the concrete slab according to building codes. Common supply headers can be installed in the slab eliminating the need for additional above slab connections. Circuit lengths in series and parallel patterns can be designed for balanced flow rates which keeps the heat evenly distributed throughout the conditioned space according to design while eliminating dependence on balancing devices to perform this function. Since no joints are allowed in the concrete in plastic (PEX) and rubber tubing systems, the results are uneven and lengthy tubing circuits in serpentine patterns. These circuits are sometimes designed 300-500 feet in length which naturally promotes spotty heating because the hot water at the beginning of the circuit loop becomes too cool by the time it reaches the end of the loop. A copper system is designed with much shorter loops, usually under 200 feet in length, which increases efficiency and promotes even floor temperatures, especially important on exposed floors. Both supply and return manifolds are required in plastic and rubber systems while only a return manifold is needed for the copper system. In fact, a properly designed copper tube system will allow efficient and even heating of the conditioned space without any balancing requirements, whereas balancing is usually required in the plastic (PEX) and rubber tube systems. The return manifold in the copper system is used only for personal comfort, i.e., reducing the heat within a zoned area, not for promoting heat. This situation lends favor to the copper system because the heating of the structure is relying on the design and not the balancing at the manifold. Even if the manifold is balanced properly in a plastic or rubber system, different tubing lengths resulting from the design limitations will prevent similar water temperatures throughout the tubing circuits. Clearly the limitations of the materials affects the overall design efficiency.
• Another important aspect of the tubing choice is its ability for repair. Often during the construction process changes in plans or accidents can occur where the tubing system can be damaged. A wall might require moving or a nail might be shot into a pipe while securing a cabinet or damaged from another trade contractor performing their installation work. In these instances a damaged copper line can be simply cut out or moved and silver-brazed back together and covered meeting code requirements. In a rubber or plastic system the tubing cannot be repaired to code. Unions, compression fittings or rubber clamps must used to reconnect the tubing circuit and should not be covered with concrete. Each repaired area requires a knockout access panel in the floor for any future service. This can be a large problem since the repairs are not as strong as the original tubing system. Unions, compression fittings and clamps can easily leak over time. Also, all the plastic to copper joints for the system manifolding and connection into the boiler system are unionized or crimped. These joint connections have had problems too. A silver-brazed copper joint is stronger than the pipe itself and a permanent installation and repair.
• Copper is also damage resistant to fire unlike the other materials which can be permanently affected and even toxic if subjected to burning.
• Copper ranks number one against oxygen permeabilty as well. Many problems have streamed from the permeability of the plastic and rubber tubings which have caused premature failures of the boiler safety and support equipment designed for “closed-loop” systems. Oxygen can diffuse through the piping walls from the outside environment into the system. Copper allows virtually no diffusion of oxygen into the system. These problems have led to the banning of rubber and certain plastic tubings in some municipalities. New barrier plastic tubings are being produced today which help prevent the problem, but do not completely eliminate it.
• Copper has long since been a standard in the plumbing and heating industry as well as countless other industries. For this reason it is widely available anywhere. The plastic tubing, specialized fittings and accessories are not standard but specialty products made by specific manufacturers. They are not easily available when needed for service or replacement.