Radiant Heating Tubing Design and Layout

Prior to laying and installing PEX tubing circuits, a thorough plan and system design must be completed in order to carry out installation faster, precisely and to avoid making costly mistakes.  A diagram of the system will be helpful in the future as well, should a need arise to repair the system and to avoid damage during overall residence remodeling or renovation.  A plan should provide an exact location where tubing is to be installed, layout design and length of circuits, quantity and location of manifolds, location of thermostats and other controls and sensors.

When designing a radiant heating tubing layout plan, there are dozens of factors and details that must be considered.  The following are the most important aspects that must be taken into consideration:

  • Equal Distance between the tubes within a loop - The spacing of tubing in an area affects the temperature as well as even heat distribution. PEX tubing is usually installed within a distance of 8".  Closer spacing (usually no less than 4") can be applied to areas with higher heat loss or floors with lower heat conductivity. 
  • Length of each tubing loop - The length of a tubing loop is directly correlated to the flow rate and heat output.  Long loops diminish the flow rate that can be produced, thus reducing heat output.  In addition, longer loops create uneven surface temperatures, since there is a greater variance between temperatures at the beginning of the loop and at the end, where temperature is significantly lower.  Following common industry standards will ensure optimal loop length, which varies depending on the tube diameter (from 30 feet for 1/2" tube to 700 feet for 1" tube).
  • Efficient position of manifolds - In order to minimize heat loss when hot water travels from manifold to loop, it is best to position the manifold as close to the loop as possible.  Two or more manifolds may be used for large areas.  Manifolds should also be positioned in an area where they can be easily accessed, if needed.
  • Increased heat output to areas with higher heat loss rate - There are generally two methods to increase heat output within specific areas. One way to accomplish this is to use Serpantine Pattern, where the warmest part of the loop is installed closer to area with the highest heat loss (windows, doors, exterior walls).  The second method requires closer tube spacing, so that more heat is being radiated to a specific area.
  • Maintaining even temperature within a zone - The easiest way to maintain even temperature is to keep tubes within an evenly spaced distance (assuming identical heat loss rate within the loop).  In order to decrease temperature variations even further, heat transfer plates may be installed. Since aluminum is an excellent heat conduit, the heat is evenly spread through a larger surface area.

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