With the popularity of radiant floor heat and sales rising each year more and more concrete contractors and general contractors are selling radiant floor heating systems with their projects. Radiant Floor heat creates some questions when first starting, in this article we will explain the key points of radiant floor heat and give you the confidence to start including radiant floor heat in your projects.

–by Les Graham

What are the advantages of radiant floor heat?

  • Radiant floor heat is proven to be the most efficient way to heat a building.  Compared to forced air heating it is approximately 30% better.
  • Even heat distribution – the whole floor is a giant radiator.
  • Out of sight – tubing is buried in the concrete or under floor. No bulky duct work, baseboard, ceiling tube convectors, or cast iron radiators.
  • Quiet – no loud fans, pinging baseboard, etc.
  • Radiant floor heat is better for people with allergies.
  • Very low maintenance and cleaning – duct work and tube convectors need cleaning.


Slab design considerations when using radiant floor heat?

The main consideration is the use of insulation – both under the slab horizontally, and vertically installed around the perimeter. The perimeter insulation needs to have an R – value of 10. Generally, this is done with 2’’ blue or pink polystyrene. If possible, incorporate this 2’’ foam as part of the original concrete forms. This can save hand digging later, which can undermine a monolithic slab.

The thickness of the slab does not have to change because of radiant floor heat. The base you normally use underneath does not need to be changed. (Personally, I like to see a 6 mil. vapor barrier under the slab.)


Do I need to insulate under the slab?

You need to consider insulation under the slab. Heat does NOT rise, but travels in all directions – hot air rises. Generally speaking, you should always insulate a project 2000 square feet or smaller with an R-value of 5 – 10. On larger projects, consider the dampness of the soil below. If you are high and dry, you can consider zero insulation, or insulate the first 6-8 feet in from outer edge. If the water table is high in an area, then insulation under the whole area becomes necessary. Under concrete there is no benefit or need for reflective type insulation.


Where is the tubing placed in the concrete?

The tubing can go in the middle or at the bottom of the concrete. Both have advantages. When placed in the middle of the concrete, the heat is delivered a little faster, thus allowing for a slight gain in efficiency. Snowmelt systems should always be installed in the middle of the slab. When placing tubing in the middle of the concrete, keep in mind that with shops you need a minimum of 1-1/2 inches of concrete above the tubing, homes require a minimum of ¾ inch above.

The advantages of the tubing placed at the bottom of the concrete are several:

  • I feel the tubing is more protected during the pour of concrete. The tubing is not suspended on the re-rod waiting for someone to ‘step on it wrong’.
  • It is more protected during the lifetime of the slab because it is farther away from drill bits, nails and screws.
  • Ease of installation: There are special staples and screw clips that utilize the use of tools that allow you to fasten to the Styrofoam from a standing position. These methods are also considered faster than attaching to the re-rod.
  • When placed at the bottom of the concrete, I feel the tubing is also a little more protected in the event of a crack. Because the tubing is not totally encased in the concrete – the bottom of tubing is against the foam or other base – it should be more protected.


Can I place the tubing in the sand below the concrete?

«read part two of Hydronic Radiant Floor Heat 101

Radiant floor heat installed in a County Maintenance  building in Illinois.


Radiant floor works well with colored concrete.  Farmers love the efficiency of radiant floor heat. 



Post Frame buildings and Steel buildings are  common applications for floor heat.



Notice the Pex-Al-Pex staying flat on the Styrofoam. Air test is on tubing and ready for the concrete.


Les Graham is the president and owner of Radiant Outfitters based out of New London, Minnesota. Graham has 24 years of experience in radiant floor heating and has certified with the Radiant Panel Association.

Radiant Outfitters, a wholesale distributor, offers complete design service and product, partnering with all types of contractors that install radiant floor tubing.

For more information, call 877.855.2537, or visit www.radiantoutfitters.com.