(C) Daniel FriedmanRadiant Heated Floor Slab Tubing & Fluid Choices

  • RADIANT SLAB TUBING & FLUID CHOICES - CONTENTS: Radiant heat slab tubing: suitability of rubber or plastic tubing for radiant-heated concrete slabs. Choices of heat-conducting fluids for use in radiant-heated concrete floor slabs. Comparison of copper, polyethylene tubing, PEX tubing for radiant heat floor slab installations.
  • POST a QUESTION or READ FAQs about the different types of tubing & fluids used with radiant heating systems

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Radiant heat tubing & heating fluid choices, advice:

This article discusses the suitability of various tubing materials for radiant heated concrete floor slabs, and choices of heat conducting fluids for radiant floors.

Our page top photograph shows polyethylene tubing being installed in a new concrete floor slab for radiant heat in a Two Harbors Minnesota building.

We also provide a MASTER INDEX to this topic, or you can try the page top or bottom SEARCH BOX as a quick way to find information you need.

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Radiant Floor Slab Tubing & Fluids: Choices, Features, Advice

Radiant floor tubing (C) Daniel FriedmanAccompanying text is reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Our page top photo shows polyethylene tubing emerging from a radiant-heated floor slab under construction in Two Harbors, MN in 2007. Note the nice detail, use of a larger diameter tubing around the heating distribution plastic tubes, protecting the heating tubing from bending damage where it emerges from the slab.

"Radiant Slab Fluids"

The question-and-answer article about radiant slab fluids and radiant slab tubing, quotes-from, updates, and comments an original article from Solar Age Magazine and written by Steven Bliss.

Questions about radiant slab floors: 

What is your opinion about the relative suitability of various plastics (e.g. polybutylene, EPDM, etc.) for carrying heat transfer fluids in concrete radiant slab floors?

Which radiant floor slab tubings are acceptable for use with water, propylene glycol, Syltherm 444? -- C.R. MC, East Lansing, MI

Answers about radiant floor tubing and fluids:

Both copper tubing and plastic poly or PEX tubing are used in radiant heat systems. Our photo (left) shows brass or copper connectors used at the transition from an electric boiler to in-slab radiant tubing. These fittings should have not been used in the concrete itself.

Plastic piping or tubing used for radiant heating systems varies in wall thickness, density, and chemical composition.

Plastic radiant heat tubing (C) Daniel Friedman

Consequently, each grade of plastic tubing that might be considered for radiant heated floors has its own temperature, pressure, and chemical compatibility limitations.

High-temperature polybutylene pipe is rated for 200 degF continuous use at 80 psi with water and/or glycols used as heat transfer fluids.

This makes polybutylene piping applicable to many radiant floor designs including the radiant floor design shown in the photograph at the top of this page.

The two radiant heat ubing sizes used most often in radiant heat floor designs are 7/8" Poly tubing or 1/2" PEX tubing. Compared with traditional copper radiant heat tubing, use of these newer materials often reduces the number of connectors and thus the risk of leakage, and easy-radius bends in tubing also improve fluid flows thorugh the system.

Radiant Floor Tubing Choices: diameters, BTUs per foot, temperature & pressure ratings

Radiant floor heating zone manifold (C) D Friedman R ArlyckWhen installing radiant floor heat tubing in a concrete slab in new construction there should not be an issue with tubing bending radius nor spacing constraints.

However when installing radiant heat tubing beneath a wood-framed floor the spacing of the floor joists and other obstacles becomes a consideration when planning for tubing bends, turns, and routing.

Our photo illustrates the radiant floor heating zone manifold for a multi-zone system installed during reconstruction of a home in Tivoli, NY. Copper piping feeds heating water to the zone manifold which in turn distributes heating fluid to four individual heating zones.

7/8-inch Polyethylene Tubing Radiant Floor Heat Tubing

Larger-diameter 7/8" Poly radiant floor tubing spaced 16" on center provides about 50 BTU's per linear foot (depending on heating fluid temperature and flow rate through the tubing.

Using this larger diameter radiant heat floor tubing will reduce the bending radius available for turns at the ends of tubing runs but it can usually be fit successfully in conventional wood-framed 16-inch on center floor joists.

1/2-inch PEX Radiant Floor Heat Tubing

PEX Plastic piping (C) Daniel FriedmanWhere there are radiant heat tubing bend radius concerns consider using 1/2" PEX that is capable of tighter bends.

However 1/2-inch PEXC tubing generates about 25 BTU's per foot, so to obtain the desired radiant floor heat capacity you should space the tubing runs closer than with larger tubing - thus you will increase the total linear feet of tubing used and the project installation cost increases a bit for this material. Use spacing of 8" on center.

Photo at left shows PEX tubing used in a water supply installation.

For radiant heat applications operating at higher temperatures or pressures (such as snow melt installations) 1/2-inch PEX tubing may withstand these conditions better than larger-diameter poly tubing but in all installations you should be sure to compare the temperature rating for your tubing with the intended use and operating system temperatures and pressures.

Watch out: in some wood-framed floor radiant heat installations where radiant heat tubing odors were a complaint, in new installations the installer may recommend running the system continuously at higher than normal temperatures for several days in a hope to "cook out" odors. But operating the system at temperatures above those for which the tubing is rated may cause damage or leaks.


Details about PEX tubing and other plastic tubing choices are at

EPDM Tubing Used for Radiant Heat Installations

Radiant floor tubing types (C) Daniel Friedman

EPDM tubing, the type used in SolaRoll™, will handle up to 300 degF. for water and glycols.

Neither EPDM tubing nor polybutylene tubing is recommended for use with silicone oils or hydrocarbons [so watch out when choosing the antifreeze product to be used in radiant heat floor systems when this tubing is selected].

Our photo (left) illustrantes Entran 3 radiant heat tubing. See Entran-II leak discussion in the FAQs section below.

High density polyethylene tubing, not the type commonly found in retail building outlets, can also handle water temperatures typical of radiant heat floor systems, but with glycols and silicone oils, temperature limitations apply.

For a given radiant floor heating application, it would be wise to consult with the manufacturer of the specific tubing material and its connectors before making your purchase. Some manufacturers do not recommend the use of brass fittings embedded in concrete. If possible, buried tubing joints should be avoided altogether.

Here we include solar energy, solar heating, solar hot water, and related building energy efficiency improvement articles reprinted/adapted/excerpted with permission from Solar Age Magazine - editor Steven Bliss.

Original article

A link to the original article in PDF form is immediately below

Solar Age Magazine Articles on Renewable Energy, Energy Savings, Construction Practices

Entran II radiant heat tubing

Please see our discussion of Entran II tubing leaks now found at RADIANT SLAB TUBING LEAKS


Continue reading at RADIANT SLAB TUBING LEAKS or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.


Or see RADIANT HEAT - home


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