What tubing should I use for my radiant panel?

Today there are many different choices of tubing materials to use for radiant panel systems. The common promoted materials are copper, plastic (PEX), and rubber tubings. The answer to this question is not found in deciding which one will work since in a properly designed system all of the tubings can perform adequately to heat the space. The answer should be to determine the best overall trouble-free tubing since it is generally an embedded structure of your home and not easily accessible. The following information is derived from over 75 years of experience and three generations of knowledge in the hydronic radiant heating field. It is unbiased, backed by common sense, and supported by countless examples and reviews of installed systems during the past decades. Although our opinions may seem biased and directed towards a particular material for the radiant panel, they have been derived from an unbiased evaluation of the system characteristics and other variables including workmanship, environmental factors, design, and material performance. ANDERSON RADIANT HEATING is committed to providing completely accurate information and hold our opinions to the highest standards. We are not married to any particular tubing product and support our material choice in representing you, the consumer, with the best possible products for the installation. We believe that soft tempered Type “L” copper tubing is the best choice for the radiant panel. We install both copper and Pex tubing radiant panel systems.  We prefer to install an aluminum barrier pex piping when our jobs call for it.  Cost factor is usually the basis for using the PEX tubing since copper is usually much more expensive to buy. But without cost concerns copper is our favorite choice.  It is true that in certain cases, conditions may exist which may compromise the integrity of any material. With historical knowledge, experience, and field observations we base our tubing choice in reference to a properly designed, engineered, and installed system controlled by ideal construction parameters. Nine times out of ten when one walks on a job site using hydronic heating the first item mentioned is that plastic (PEX) tubing is the common choice for the radiant panel. Due to over-marketing, misinformation, lack of experience, and installers wanting to be part of the “latest and greatest” mentality, these products continue to be promoted without the long term view and proven performance record. It is in your best interest as a consumer to have direct knowledge about the choices and products your local contractor provides. Remember, ANDERSON RADIANT HEATING has nothing to gain by promoting a particular opinion since we can install any tubing desired by a consumer. Our efforts at providing real information is an extension of our integrity and dedication fueled by our passion of what we enjoy doing, namely radiant panel heating.
Copper Development Association - Comments about copper tubing
When comparing each of the tubing materials, copper is superior in its heat transfer abilties, pressure rating, temperature rating, system design parameters, repair, strength, defense to oxygen permeability, availability, and flame resistance.
  • 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.
The reasons for the failure of copper, plastic (PEX), or rubber panel systems should be examined. First, let’s identify two distinct differences. The problems associated with the plastic and rubber tubings have resulted from failures and limitations of the actual materials themselves, while the problems with copper tubing have been only associated with the construction parameters. In conclusion, copper has not failed as a material as with the plastics (PEX) and rubber tubings, but only because of human factors. We have seen failures with rubber tubing in hot water heating applications just after a few years use. The constant heat of the water and possibly the water content has resulted in the deterioration and cracking of the rubber product. Several class action lawsuits for water damages from leaks have been filed against some of the manufacturers. Lawsuits also have been filed in some states against plastic tubing manufacturers for leakage at many of the manfolded joints. We have observed the tubing becoming hard, annealed and brittle after extended use. Hairline splits have occurred in the tubing circuits which run the length of large sections of the building. Anytime you have unionized, crimped, or compression fittings, the potential for leakage and related problems is greatly enhanced. These problems have arisen in these materials under normal use and service. Let’s examine some of the problems and myths associated with copper tubing systems. First there is concern the copper will fail due to corrosion from contact with dissimilar metals, concrete elements, and electrolysis. Second, there is concern that the tubing will leak due to stress created by cracks in the concrete. Now all of these problems have been true at some time and someplace, but largely have to do with the architectural design, system installer or subcontractor workmanship. The truth is that a “closed-loop” copper radiant panel system will never deteriorate or leak if properly installed and will last the lifetime of the structure without question. Since there is no introduction of new oxygen and minerals into the tubing system because of the “closed-loop” design, the degradation process is eliminated and cannot occur. In the San Francisco Bay Area during the 1950’s through the 1970’s, thousands of slab tract homes were built using copper tubing in both the radiant heating systems and domestic water systems. We have seen degradation occur in some “open-loop” domestic water systems due to the conditions surrounding the method of installation including dissimilar metal contact, improper electrical grounding and with stray voltages, acidic soils, and constant inflow of oxygen and salts from the city water. It is improper to compare an “open-loop” domestic water system with the performance and longevity of a “closed-loop” radiant panel system. Click here for further explanation regarding concerns about copper tube degradation. A majority of these tract homes have never experienced any leakage. Some have had leakage problems due to stress related factors rather than degradation factors. Because these homes were built on improperly compacted soils, contained insufficient rebar for slab reinforcement and thin non-uniform slabs, they were susceptible to repetitive slab movement. From decades of grade stress and slab movement, some leaks developed since the tubing was bound so tightly in the concrete the tube was simply stretched and split across perpendicular cracks. It is a fact that all slabs crack, but whether or not they move or not is dependent on their reinforcement and foundation configuration. We believe any material when subjected to these immense forces would have failed. Overall we feel the copper tube has performed outstandingly within the circumstances. The average amount of leaks found today in one of these slab homes after 30-45 years of grade stress is only 1-5. With as many cracks that are visible in these slabs and how many feet of copper coil cross these cracks installed 12-15 inches on center, failure has been an amazingly low occurance. We have developed techniques which can pinpoint any leaks and because of the copper tube, they can easily be repaired. After having repaired thousands of these leaks due to this poor slab construction, we have never observed in over 45 years a single case where the copper tubing was degraded, when properly installed. The copper tubing has appeared “as-good” as the day it was installed without any signs of corrosion. There has been no more than three times we have observed the radiant panel copper tubing degraded and it was due to the system being operated within an “open-loop” domestic water system which is subjected to the conditions required for degradation to occur. We know the difference of system performance with proper construction because of the thousands of custom homes built in our area during the same time frame. We have rarely experienced a problem with stress related failues in these custom homes with monolithic pours and properly re-inforced concrete slabs. Also, we have never seen a leak occur in a home built with a two-slab pour which has a structural slab foundation poured first and then a topping slab containing the radiant panel, or a radiant slab poured on wooden sub-floor framing, since both slabs are raised, floating, and stress free. The plastic systems were being introduced really for two reasons: 1) to reduce the installation cost; 2) to perform better than the copper or steel systems which were the common choice. Installation costs were cheaper because the systems rolled in faster but the material cost was nearly the same. Today the proper barrier products (PEX) equivalents, manifolding, and custom controls costs more per square foot in materials than installing a copper system. The only quality where the plastic tubing exceeded the performance of copper was in its malleability. It has more flexibilty than copper. However, if the element of stress is removed, i.e., installing the radiant panel on a wood sub-floor, two-slab pours on grade, or a monolithic pour on grade with proper slab reinforcement, there is absolutely no reason why copper shouldn’t be chosen over plastic or rubber tubings since copper far exceeds the performance in all other ways. And it is being chosen more and more. As people learn the real story behind the misinformation of corrosion and failure in copper radiant panel systems and leakage, the plastic and rubber tubing products can’t compare and obviously look much less attractive for this application. Actually copper is experiencing a resurgence in the radiant heating market and even some plastic installers are providing secondary bids to install copper. Copper may run a little more expensive to install but many people are once again learning the very hard way that cheaper is definitely not always better. There has also been some resistance to the use of copper because of the perception that it has a tendency to corrode when in contact with concrete. The objection may have been based on failures of copper tubing at the Levittown development in New York State some 50 years ago. Those failures have been attributed to the high levels of sulfur in fly-ash which was the ingredient in the Levittown concrete slabs. Isolated cases like this stem from an improper concrete mix which teach us by example what not to do. Copper should not be used anywhere the concrete mix results in an elevated sulfur or lime content. Standard concrete mix or tile mortar will not affect the copper tubing at all. From over 50 years of performance in the market and extensive system evaluation copper is regarded by many experienced radiant heating specialists to be the proper common choice material for radiant heating applications. From our point of view, you have one shot at choosing the best system material to be permanently encased in your home. Through comparison and experience, there is clearly one predominant choice – Copper. Copper Development Association - Comments about copper tubing Argument regarding copper tube degradation in closed-loop radiant panel systems

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