Installing Schluter DITRA-HEAT-DUO Over Concrete Floors

By Robert Robillard on Electrical, Remodeling

Solving A Cold Basement Floor With Electric Radiant Heat

We were recently asked to install electric radiant floor heat in a basement bathroom, concrete floor.  The problem with concrete floors is that the cold concrete absorbs heat energy, significantly decreasing the time it takes for the tile floor to warm up.  In some cases, floors may never reach the desired temperature.

This is even more an issue when there is no insulation layer below the concrete, which was out case. While I have installed floor heat in many spaces, the thought of electric radiant heat on cold concrete subfloor seemed like a waste.

Adding Heat To A Cold Basement

This particular bathroom had no heat source and no way to add it from the existing system, so electric radiant heat not only made sense it was the most logical solution.

Installing Radiant Heat with A Thermal Break

So how did I decide on Schluter DITRA-HEAT-DUO. I learned was that Schluter makes a uncoupling membrane that provides a thermal break [cold break] from the concrete substrate.  The product is called Schluter®-DITRA-HEAT-DUO.

Schluter-DITRA-HEAT-DUO is an uncoupling and waterproofing membrane with an integrated bonding fleece that can also be used to reduce sound transmission between floor –ceiling assemblies. The best part is that it solved my issue of heat loss through the cold concrete floor. The DITRA-HEAT-DUO has fleece liner that results in a 70% faster floor warming response time.

Schluter DITRA-HEAT-DUO Benefits

The Schluter-DITRA-HEAT-DUO membrane is 5/16″ (8 mm)-thick, [compared to DITRA-HEAT at 1/4″ (5.5 mm)-thick]and has 4 Benefits:

  1. Sound Control
  2. Floor Warming
  3. Decoupling
  4. Vapor management

Installing Schluter-DITRA-HEAT-DUO

The Schluter DITRA-HEAT-DUO  come in both a roll or by the sheet and has a stud designed to allow for the easy installation of DITRA-HEAT-E-HK heating cables. We chose the sheets since it was a small room, and it was also easier to cut them at the toilet and floor drains.


When planning your system ensure to keep a minimum spacing from the following:

  1. Plan for a dedicated electrical circuit.
  2. A ground fault circuit interrupter (GFCI) is required for each circuit. The DITRA-HEAT thermostats have built-in GFCI protection.
  3. Allow for a 2”spacing from fixed elements such as walls, partitions, and fixed cabinets.
  4. Use a 4” spacing from plumbing drains and 8” spacing from sources (baseboard heaters, fireplaces, forced air heating ducts, etc.) Lastly use a 7” spacing from centerline of the toilet.

Avoid Placing Heating Cables Under Fixed Objects

NEVER install the heating cable under vanities, bathtub platforms, free standing bathtubs, kitchen cabinets and islands or any other fixtures or in closets. Excessive heat will build up in these confined spaces and may cause cable overheating.

The minimum installed bending radius of the heating cable is 0.5 inches

Preparation For Schluter DITRA-HEAT-DUO Installation

  1. Wipe down and clean the concrete floor substrate.
  2. Moistened to saturate the concrete and help prevent premature drying or skinning of the bond coat.
  3. Dry fit your parts on the floor.
  4. Use an unmodified thin-set mortar , apply the thin-set mortar (mixed to a fairly fluid consistency, but still able to hold a notch)
  5. Trowel thinnest with a  1/4″ x 1/4″ square-notched trowel.
  6. Install and embed the matting into the mortar using a float.
  7. Lift up a corner of the matting to check coverage. Proper installation results in full contact between the fleece webbing and the thin-set mortar..
  8. Abut end and side sections of adjacent sheets, ensuring alignment between both sheet studs
  9. Heating cables may not touch, cross over, or overlap one another.
  10. Ise a dedicated wire chase for the cold lead and sensor wires. [see photo below]

Test Heating Cable

Heating cable testing is required while the heating cable is on the spool and twice during installation.

  • Test 1: Conductor Resistance
  • Test 2: Continuity between Conductor and Ground Braid +
  • Test 3: Insulation Resistance
  • Test 4: Thermostat Floor Temperature Sensor

Floor Heat On A Concrete Floor

Now when the electric heat kicks on the tile  floor warms fast and concrete subfloor absorbs LESS heat energy.

PRO Tip: Because this bathroom is in an unheated basement we added a door-closer mechanism to the door to keep the door closed, at all times, for heat conservation and to prevent the thermostat from activating more than needed.


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About the author

Robert Robillard

Robert Robillard

Carpenter / Remodeler / Editor / Writer / Video Talent

Robert Robillard is a remodeler, general contractor, and principal of a carpentry and renovation business located in Concord, Massachusetts. He also writes the "Ask the Carpenter" advice column in the Boston Globe, and serves as the Editor of Tool Box Buzz and founding editor of A Concord Carpenter . Rob is in charge of our Tool and Product Review - Tool and Product Review - Video Channel, , where we post all of our tool reviews and video tutorials. Rob enjoys using his knowledge and experience to help and educate building professionals as well as DIYers on best practices in the remodeling industry. The Concord Carpenter's motto: "Well done is better than well said!" : Read more about Rob <a href=""

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