Volume 31, number 3, November 2017

Radiant floors: A technology that’s geared for comfort

Radiant floor heating is drawing keen interest from builders for a wide variety of applications, from municipal housing to upscale dwellings and even commercial buildings. In fact, its strong performance and ability to produce a more comfortable heat are making it very popular. To ensure the radiant flooring will function well for the entire life of the building, it is important to properly design it and carefully supervise its installation and initial start-up.


00043_lrDesign and installation: the key elements

During the design phase, the empirical measurements for the project can be used to estimate the preliminary budgets. However, to precisely define the tubing networks in compliance with CSA B214 – Installation code for hydronic heating systems, the load calculations and dimensioning should be done with specialized radiant flooring software. The distributors of these solutions can help you with this. Several user-friendly tools recommended by multiple tubing manufacturers are also available, such as LoopCAD1. However, for buildings with more complex architecture, nothing beats an experienced designer using AutoCAD.

As for installation, it’s best to hire specialized contractors, because optimizing the designs takes close collaboration between the engineer, who defines the heating loads of the spaces, the plumbing or pipefitting contractor, who establishes the initial tubing layout and determines the installation constraints, and the equipment distributor, who confirms and adjusts the individual tubing networks using specialized softwares. And lastly, everything has to be coordinated with the general contractor and the architect, who will determine if the strategy is acceptable based on the related schedules and, in particular, the concrete pours.

Ignoring these first steps can result in losses or in surpluses of more than 15% in the quantities of tubing required relative to the empirical measurements taken2. The resulting impact, which is substantial over the hundreds of thousands of linear feet of tubing installed in multi-dwelling projects, can reduce the economic competitiveness of this solution. Finally, care must be taken with the initial start-up and balancing, as noted in an article in the journal IMB3.


Optimizing the systems for comfort by factoring in building inertia

The system control has to consider that it’s the concrete mass that is heated by the radiant flooring. It has to adequately understand and anticipate its behaviour. For example, if this concrete mass is maintained at an overly high temperature in a condo building with a concrete structure, the adjacent units will be kept at a temperature that is “too high” and could become problematic with the contributions of the midday sun.

Several projects favour the approach of using the radiant flooring as the first level of heating to cover 75% to 80% of the dwelling’s requirements. Additional heat is then provided by an auxiliary forced-air system connected to the air-conditioning system, which allows for faster temperature makeup and control. Note that this rule of thumb should be adjusted based on the type of building and its use. For example, in a warehouse, 100% of the load could be covered by the radiant flooring.


Image courtesy of Uponor.

Image courtesy of Uponor.

The insulation beneath the slab is also crucial with radiant floors. Indeed, without insulation the thermal loss below the slab can be as high as 15 BTU/hr/ft2, the equivalent of the heating load in some cases. A minimum of R10 insulation is therefore recommended.


Image and texts taken from the Gaz Métro sheet on radiant floors.

Finally, using the right controls is essential to achieving the desired comfort. Many components specifically designed for heated floors, such as thermostats, collectors and valves, are readily available and supplied by the tubing manufacturers (Uponor, Watts, etc.).  The control strategy will determine the type of configuration recommended.


Annotated image courtesy of Uponor, “Complete Design Assistance Manual.”


Although there are a great many books on radiant floors, CSA B214 – Installation code for hydronic heating systems is a useful, if not essential, reference for most projects.


Increased supervision and precautions for the installer

To ensure the system’s durability, it is crucial to consider the expansion joints that must be created in the concrete slab. In many cases, sleeves can be used to cover and protect the tubing in the expansion joints created in the slab.

As well, planning beforehand to use insertion plates for the expansion joints can be helpful to avoid having the joints created by saw cuts in the slab containing the radiant floor tubing.

These precautions require considerable coordination and will slow the construction pace unless the circuits are designed from the outset so the tubing never crosses expansion joints, or does so as seldom as possible.


Key applications for radiant flooring

Radiant flooring is very well suited to the following building types:

  • Low-rent housing, thanks to its durability and integration into the building structure. Their low maintenance costs and efficiency make radiant floors an unbeatable solution for these buildings, a fact the Sorel municipal housing bureau understood for its housing designed by ConceptR.
  • Upscale dwellings: Many builders incorporate this solution in order to exceed industry standards and set themselves apart with innovative projects (durable buildings, retirement homes, etc.).
  • Automobile dealerships and showrooms with large glass walls and high ceilings.
  • Drafty warehouse and garage environments: With a concrete slab floor, it’s easy to install the tubing during construction to counter the effects of air stratification and leverage the slab’s inertia in cases where doors are opened frequently.

In these applications, the overall architectural savings can be attractive. According to a recent study by the Natural Gas Technologies Centre (NGTC), in addition to being the trend, polished concrete varies in cost from $1 to $12/ft2. This option is very appealing for large surface areas, enabling savings relative to the cost of traditional floor coverings such as ceramic tile ($5 to $11/ft2) or engineered wood ($6 to $12/ft2). So the extra cost of the heating solution can be partly offset by the savings in floor coverings.

Another very interesting application for heated floors is melting snow. In fact, for safety reasons, most underground parking projects these days include radiant heating under the access ramp.


Energy efficiency: considerable gains

On average, the energy gain from radiant flooring is equivalent to lowering the air temperature 1 to 2oC (+/-1.8 to 4oF) for the same level of comfort, which generates substantial savings, as the following table shows:

Percentage of savings according to the « Lowering the ambient temperature » program

Selected periods for the « Lowering the ambient temperature » program
Abaissement Continuously Day Night Weekend
Number of degrees day and night 9 a.m. to 6 p.m. (five days/week) 9 p.m. to 6 a.m. (seven days/week) Fri. 9 p.m.  to Mon. 6 a.m.
1 7,1 % 1,7 % 2,8 % 2,4 %
2 13,6 % 3,4 % 5,4 % 4,7 %
3 19,7 % 4,9 % 7,9 % 6,8 %
4 25,4 % 6,2 % 10,2 % 8,7 %
5 30,7 % 7,5 % 12,3 % 10,5 %
6 35,6 % 8,7 % 14,2 % 12,2 %
7 40,1 % 9,9 % 16 % 13,8 %
8 44,4 % 10,9 % 17,7 % 15,2 %
9 48,3 % 11,9 % 19,3 % 16,6 %
10 52 % 12,8 % 20,8 % 17,8 %

Table taken from the Gaz Métro sheet “Lowering the ambient temperature.”


What’s more, combined with a condensing boiler, this solution is very efficient and helps reduce the energy consumption of the building, often making it eligible for Gaz Métro’s financial assistance programs.


High-potential market and skills to master

The heated flooring market currently represents only around 5%4 of the mechanical systems installed. However, given the possible applications, there is considerable development potential.

The availability of new products that make heated flooring more accessible is undoubtedly contributing to the strong interest noted lately in many projects, among other things. Nevertheless, a solid understanding of this solution and its basic concepts is still required to integrate it into a building easily. Several resources are available to create added value in your projects.


Mathieu Rondeau, Eng., CEM, CMVP, LEED GA®
Advisor, Technologies and Energy Efficiency, DATECH Gaz Métro


2 Harvey Ramer, July 7, 2017, “It’s Not Just Tubing in Concrete” by PHCPPros.com https://www.phcppros.com/articles/5587-its-not-just-tubing-in-concrete
3 Jean-Claude Rémy, November 2015, “Diagnostic de défaillance des systèmes hydroniques,” Inter Mécanique du Bâtiment, VOL. 30, No. 9
4 Source: Uponor