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Articles PEX Tube Sizing and Spacing

How to determine PEX tubing size and spacing for your project

There are several ways to size an RHT PEX tubing and manifold kit for your shop, hangar or residence. The simplest way to determine the amount of pipe you will need is to first choose the appropriate tube size and spacing for your application, then determine the overall lineal footage of tubing based on the square footage multipliers listed below.

For residential applications as well as small to medium shops and garages O2 oxygen barrier PEX tubing is standard. With ½" pipe a 6" pattern is sometimes used in bathrooms and for extreme cold climates, 8" and 9" patterns are standard for most living areas in most climates, and a 12" pattern is used in garages and living areas in warmer climates. For most large shops and small commercial applications ⅝" oxygen barrier PEX tubing is typically used. With ⅝" tubing a 12" pattern is standard, but a 16" pattern can be used in warmer climates or when a very low ambient temperature is desired. For large shops and large commercial buildings (usually over 5,000 square feet) ¾" oxygen barrier PEX pipe is standard. With ¾" tubing either a 16" or an 18" spacing is used, depending on the climate and the desired temperature for the space.

Now that you've chosen a size and spacing of PEX tubing for your project, simply multiply the square footage of the space to be heated by one of the following multipliers to determine the overall lineal footage of pipe that you will need. Be sure to use the correct multiplier that corresponds to the spacing you have chosen:

  • 6" spacing = sq. ft. x 2.0
  • 8" spacing = sq. ft. x 1.5
  • 9" spacing = sq. ft. x 1.34
  • 12" spacing = sq. ft. x 1.0
  • 16" spacing = sq. ft. x .75
  • 18" spacing = sq. ft. x .67

Once you have determined the actual combined length of pipe you will need, the next step is to determine the number of loops or circuits of pipe. With ½" tubing a circuit length of 300' is standard, but circuits anywhere from 250' up to 350' are within the range recommended by the Radiant Panel Association. With ⅝" and ¾" tubing, 500' circuits are standard. So for example if you are using ½" tubing and have determined you will need 900' of pipe, you will have three circuits of 300' each and a 3 port manifold. If you are using ⅝" tubing and have determined you will need 3000' of pipe, you will have six circuits of 500' each and a 6 port manifold.

If you need additional help determining sizing, spacing, and/or layout of PEX tubing for your project, BlueRidge Company will be pleased to assist you with that. We offer free design services and tubing layout with purchase of tubing and manifolds. Simply visit our Free Radiant Design page, and fill out the design request form to receive a free estimate of the materials required for your project:

For all in-slab applications BlueRidge Company recommends using one of the following insulation products to maintain efficiency and minimize unnecessary heat loss (listed in order of effectiveness):

  • 1. FOAMULAR 250 2" rigid foam Insulation R-10
  • 2. FOAMULAR 250 1 1/2" rigid foam Insulation R-7.5
  • 3. FOAMULAR 250 1" rigid foam Insulation R-5
  • 4. Barrier ⅜" insulation R 1.7
  • 5. Bubble Foil Bubble (marginally better than nothing)


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