Grade of Copper Tubing Used in Hydronic Boiler Systems


Boilers do more than heat the water for your morning shower. In homes with a hydronic system, the boiler helps to heat the home. An integral part of this system is the copper tubing that runs through the house. The grade of copper tubing used for hydronic systems is not the same as the copper pipe used for plumbing. Determine the type of tubing you need before repair or installation of a hydronic system to avoid future problems.

Hydronic Systems

  • Hydronic systems warm your home with water flowing through tubing or pipes to baseboard heaters. A boiler heats water to just below boiling. The heated water flows through copper tubing to baseboard heaters in your home where it slowly and evenly heats the room. Once the heat from the water has been spent in the baseboard heater, the water returns to the boiler through a separate set of pipes. Radiant systems have the copper tubing built into the flooring of the room to slowly heat the floor from the hot water in the pipes.

Why Copper Is Used

  • Copper is the material of choice for hydronic systems because it is a highly conductive metal. It will easily transfer heat from the water inside the pipe to the baseboard heater in the room. You would not be able to do this with cast-iron pipes, because they slowly transfer heat and your room would never get warm.

Types of Copper Tubing

  • Copper tubing grades indicate the thickness of the pipe. The diameter of pipes with grades K, L and M is the same, but the tubing is of decreasing thickness the higher in the alphabet the grade. With high-pressure water systems, you would need a thicker tubing, but hydronic system tubing needs to be thin enough for easy heat transfer from the hot water through the copper tubing to the baseboard heater.

Copper Tubing Grades

  • The grade of copper tubing used in your hydronic system will depend on the type of hydronic system you have. If you have a system that heats with baseboard heaters or radiators, John Siegenthaler in "Modern Hydronic Heating for Residential and Light Commercial Buildings" recommends the thinnest grade M copper tubing to allow for the best heat transfer. Radiant flooring systems are slightly different, because the copper tubing is built into the floor, so it must be stronger. For ease of installation and strength of support, "Audel HVAC Fundamentals: Volume 2: Heating System Components, Gas and Oil Burners, and Automatic Controls" by James E. Brumbaugh recommends using grade L copper tubing.

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