I’m not sure how many of you contractors out there have installed an electric radiant heat system under tile, hardwood or other flooring products, but if you have and were able to feel the warmth radiating from the floor, you already have some level of confidence in selling and installing these types of systems. For those of you who haven’t had the opportunity to install an electric radiant system, there are a few basic things you need to understand to make the installation go smoothly.

Whether we’re talking about electric or hydronic systems (which use heated water for warmth), the most important step is to do your homework. Find out if the flooring product is even suitable for installation over a radiant system. There are several different types of electric radiant heating systems out on the market and if you’re not familiar with what each does, you can get yourself into trouble.

Before you get too far into the estimate, you will want to either already know a good electrician or let your customer know they will have to hire their own. The reason for this is the hookup at the wall to the power source. A licensed electrician will determine if the power source is adequate to run the system or if additional wiring will be required.

Make a diagram of the area where you want to install a radiant system, along with the location of the tie in to power. Manufacturers of electric radiant can help you determine the amount of pads or wire necessary to heat the area, so use their services to assist you. Depending on the amount of heating elements required for the area, you’ll either choose a 110- or 220-volt unit (Photos 1 and 2).

Also, let the manufacturer know if there is going to be an area rug or large furniture in the radiant areas. Area rugs/pads and large pieces of furniture can inhibit the heat from radiating out and away from the floor, and may create problems with some floors.

If you’re estimating flooring over a radiant system you’ll want a check-off sheet; here are some items to address for electric radiant:

  • Can flooring be installed over radiant systems?
  • Is there sufficient power and a connection point?
  • Does the system require its own thermostat?
  • Is there space to mount the thermostat?
  • Will the system require a reflective mat/board either directly underneath the mat or under the subfloor to make sure the heat goes upward?
  • Who’s hiring the licensed electrician?

Are there any special tools required for electric radiant? Yes. You will want an ohmmeter/multimeter to make sure that the wiring is not damaged by trowels or construction traffic. If you aren’t familiar with what an ohmmeter/multimeter does, it measures resistance in a circuit. What you want is a continuous current running through the wires. Since you will not have power supplied to the mats until the installation of flooring is completed, you will need a way to make sure you haven’t compromised the electrical system. (If you have, you may end up replacing the floor.) An ohmmeter/multimeter will have its own power supplied by a battery so you can monitor continuity as you install (Photo 3).

Hydronic systems, on the other hand, are typically installed during the building stage of the structure by HVAC contractors who specialize in radiant heat. Radiant specialists will understand heat calculations and layout their hydronic lines accordingly.

Once the PEX tubing has been installed, a topping of concrete, lightweight concrete or a gypsum-based pour (make sure the flooring manufacturers stand behind gypsum-based subfloors) is placed over the tubing. There are also some wood subfloor panels with channels for PEX tubing, which eliminates an additional topping for hardwood and laminate.

When doing a walkthrough of the installation, check to see where the supply lines and manifold are located in relation to the flooring. Make sure the system is up and running at least two weeks prior to installation. Try to have the system running so you can check for any hot spots with an infrared thermometer—you’ll be able to get instant readings of the surface temperature (Photo 4).

The maximum temperature at the surface of the subfloor will usually be limited to 80 to 85 degrees Fahrenheit by flooring manufacturers. However, PEX lines coming into the supply room will be hotter wherever they are concentrated into a smaller area. This will create a “hot spot” in these areas, so if you’re installing hardwood this could be a concern (Photos 5-7).

Checking moisture content is important for concrete or gypsum slabs. Industry standards and manufacturers will require either calcium chloride (ASTM 1869) or in-situ relative humidity (ASTM 2170) tests to record quantitative measurements. Electronic surface meters will only give a qualitative number. For lightweight concrete and gypsum-based pours, the required test method is ASTM 2170.

Installation over both types of radiant systems will require some special attention as the heat is coming directly through the flooring and not forced air vents. Allow for movement accommodation (expansion/contraction) for tile, hardwood and laminate. A moisture meter and hygrometer will also be required to check moisture content of hardwood and ambient conditions.

Always remember that radiant heat is different than a forced air system. Regulating heat is critical to the longevity of flooring. Slow, incremental adjustments will not “shock” flooring, whereas turning the system off while the end-user is not there and then turning it up when they arrive back home will cause problems. Make a point to the end-user to try to keep the system at a constant temperature to minimize shocking the flooring. If they need to make changes to the temperature, only make two-degree adjustments every 24 hours.

By the way, the Radiant Professionals Alliance (radiantprofessionalsalliance.org) annually publishes information regarding flooring over radiant systems, called the Radiant Comfort Guide. If you receive FCI, the publication already comes to you for free. If you aren’t a subscriber (which you should be; go to www.fcimag.com/subscribe to subscribe), you can purchase the publication from the RPA website.