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DITRA-HEAT Heated Flooring Systems

An Awesome Method to Heat Tiled Floors

 

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by Jeff Patterson in Bathrooms
DITRA-HEAT Heated Flooring Systems

DITRA-HEAT heated flooring systems are a great way to warm up tile floors.

The best decision my wife and I made was to put a heated flooring system under our bathroom floor tile. Our thermostat automatically warms up the tile a few minutes before we wake up.

It’s pretty awesome to have a heated floor waiting for you in the morning.

Today we share step-by-step how to install DITRA-HEAT. You’ll be ready to take on this project even if you’re a complete beginner.

Schluter DITRA is an uncoupling mat that’s placed over wood or cement subfloors. DITRA prevents tiles and grout from cracking because of it’s geometric configuration.

DITRA-HEAT uses the same technology and allows heating cables to be run in it’s stud structure. It’s a pretty cool system for DIYers or professionals.

Here are the supplies you need:

We left the prices blank for the membrane and heating cables because those depend on the size of the room. But Schluter’s online calculator will help with the rough price.

Before you install DITRA-HEAT it’s important to have the proper underlayment. You’ll see that we installed DITRA-HEAT over 3/4 inch OSB.

OSB Subfloor

Reference the DITRA-HEAT handbook to ensure your underlayment meets Schluter’s recommendations.

For example, Schluter recommends wood subfloors have a minimum thickness of 3/8″. When in doubt, always increase the thickness of the underlayment.

 

Step 1: Planning DITRA-HEAT Heated Flooring Systems

First things first, get the total square footage of your bathroom. Then deduct the areas that won’t be heated, e.g. the bathtub, vanity and toilet.

Keep in mind that DITRA-HEAT cables should not be underneath a vanity. The minimum spacing is as follows

  • 2 inches from walls, partitions and fixed cabinets
  • 2 inches from toilet flanges (you’ll melt the was ring if closer!!)
  • 6 inches from floor drains
  • 8 inches from heat sources, e.g. baseboard heaters, forced air vents, fireplaces, etc.

Schluter recommends adding a buffer zone to your floor plan. Buffer zones are helpful because it’s hard to know exactly where the heating cable will end.

This is important because DITRA-HEAT cables cannot be cut.

The buffer zone is an area where floor warming is not essential and heating cable installation is not planned (e.g., beside a bathtub or adjacent to a door opening or next to a toilet).

DITRA HEAT buffer zone

This area allows for placement of excess heating cable. Heating cables may also be installed 6″ (150 mm) from the wall to create a buffer zone.

DITRA HEAT cable

If the total current in your setup is less than 15 amps then two DITRA-HEAT-E-HK heating cables can be connected and controlled by a single DITRA-HEAT-E-RT/-RSD/-R thermostat.

DITRA HEAT Thermostat

If the total current in your setup is over 15 amps and multiple heating cables are required, you’ll need additional DITRA-HEAT thermostats. Or the DITRA-HEAT thermostat can be combined with DITRA-HEAT-E-RR power modules.

Follow local electrical codes to wire the cables to the thermostat.

 

Step 2: DITRA-HEAT Heated Flooring Systems Materials

The best way to determine how much DITRA-HEAT membrane you need is to visit Schluter’s website.

Schluter has a fantastic online calculator that helps you choose the membrane and cable.

Click here to visit Schluter’s website.

DITRA-HEAT membranes come in either rolls or mats. Rolls are good for large bathrooms and mats are for smaller spaces.

Once you figure out the DITRA-HEAT membrane square footage, order heating cable that’s slightly less than what you need.

DITRA HEAT cables

The reason for this is the heating cables cannot be cut and it’s better to have less than more. We’ll discuss this in the video.

Furthermore, we recommend getting a programmable thermostat.

DITRA HEAT programmable thermostat

That way you can program DITRA-HEAT to turn on and off when you need it most.

Thus, you’ll save money and have a more comfortable experience.

We like the touchscreen thermostat because it looks great and adds a nice touch to the bathroom.

DITRA HEAT touchscreen thermostat

Also, get KERDI-BAND to waterproof the seams of the DITRA-HEAT mats.

KERDI BAND for DITRA HEAT

You can flash up the sides of the walls with the KERDI-BAND to waterproof the entire floor.

DITRA-HEAT mats are 1/4 inch thick so Schluter recommends using a 1/4″x1/4″x1/4″ square notched trowel for the thin-set.

Trowel for DITRA HEAT

In this tutorial we set the DITRA-HEAT mat over top an OSB wood subfloor. Schluter requires setting the mat in modified thin-set so that it’s fleece side will adhere properly. We used Mapei’s Kerabond thin-set and added Keralastic to it instead of water to make our thin-set modified.

Keralastic for DITRA HEAT

Since you’re going to be on your knees it’s not a bad idea to have a set of knee pads…if you’re wondering, Steve is wearing ProKnee knee pads in the video. Their knee pads are made in the USA and great for anyone installing tile or other flooring products.

 

Step 3: Setting the DITRA-HEAT Membrane

Our bathroom in this tutorial was pretty big and required the use of a DITRA-HEAT roll.

Mix up thin-set so that it’s slightly loose but still holds a trowel ridge.

If you use Mapei’s system, add the Keralastic to a 5-gallon bucket then the Kerabond.

Keralastic First

Then mix the thin-set until it has a creamy smooth texture that’s slightly thinner than what you’d use for setting tile.

Mix Kerabond

Dry fit the first sheet of membrane. Keep the DITRA-HEAT membrane a minimum of 1/8 to 1/4 inch from walls.

Dry Fit DITRA HEAT

Cut membranes or mats using a utility knife.

Cut DITRA HEAT with a Knife

If you use the roll it’s a good idea to counter roll it.

Counter Roll DITRA HEAT

Counter rolling prevents the membrane from pulling up from the thin-set.

Clean the subfloor with a damp sponge and water.

Clean Subfloor

The damp sponge application will also stop the wood subfloor from sucking the moisture from the thin-set.

Burn the thin-set into the wood subfloor using the flat side of the trowel.

Burn Thin-Set into Subfloor

Go back over the burned thin-set with the trowel and this time make all the ridges the same direction, i.e. directional troweling.

Directional Troweling of Thin-Set

Roll the membrane into the thin-set and embed it using a rubber or wood float.

Embed Membrane

Then pull back the membrane and check for 100% thin-set coverage on the fleece.

Thin-set Coverage for DITRA HEAT

If you get any thin-set on the top of the DITRA-HEAT membrane clean it off. Dried thin-set will prevent the heating cable from properly snapping into the studs.

We positioned the membrane in the center of doorways because this bathroom is adjacent to carpeted areas.

Doorway

Double check the coverage underneath long pieces of membrane. This will prevent any issues with the membrane not sticking to the subfloor.

Lay adjacent pieces of membrane so that studs on each piece line up with each other.

Membrane Direction

PRO TIP: The DITRA-HEAT membrane needs to cover the entire floor even if you’re not going to heat a specific area. This keeps the floor level.

Owning rental properties has taught us that the toilet area needs to be waterproof. DITRA-HEAT and DITRA make this an easy process.

Place DITRA-HEAT membrane over the toilet flange and cut around it using a utility knife.

Toilet Flange

Seal around the toilet flange and DITRA-HEAT membrane using KERDI-FIX. This helps keep the floor waterproof.

 

Step 4: Heating Cable Tips for DITRA-HEAT

A dedicated circuit is required for DITRA-HEAT. If you’re not comfortable doing this yourself call in a licensed electrician. Also, we used metal conduit per local code.

Metal Conduit

Although a GFCI is required for DITRA-HEAT, the DITRA-HEAT-E-RT/-RSD/-R thermostats include a GFCI. The picture below is the back of the thermostat, it’s very similar to a GFCI.

Thermostat GFCI

Thus a GFCI circuit breaker is not required when using these thermostats. Plus, we like the touchscreen DITRA thermostat…it’s pretty cool, especially if you’re a techie. Don’t worry, we show you the complete installation of the thermostat in Step 14 and the video.

Also, heating cables must be grounded. And NEVER install a cable designed for a 120 V power source on a 240/208 V power source.

Please read the DITRA-HEAT installation handbook for all of the heating cable details. You can find the handbook on Schluter’s website.

Schluter requires three tests for the DITRA-HEAT system to retain its 10 year warranty

  • Test 1: Conductor Resistance
  • Test 2: Conductor and Ground Braid Continuity
  • Floor Temperature Sensor Test

An Insulation Resistance Test is recommended, but not required. Although, Schluter will extend the warranty from 10 years to 15 years if you do the Insulation Resistance Test.

Let’s dive into the tests one by one.

 

Step 5: Conductor Resistance Test (Required)

Set your multimeter for resistance measurement. Read your multimeter directions if you’re not sure how to do this.

Then place the red lead from the multimeter on the red wire and the black lead on the black wire from the heating cable.

Conductor Resistance

If the ohms reading taken on the power leads varies by 10% or more from the value printed on the spool this means either the cable has been damaged or the multimeter is not set properly (or it’s not calibrated).

If on the other hand your ohms reading is within 10%, your conductor resistance test is good.

Conductor Resistance

Record the ohms measurement in the Schluter heating cable tests log.

 

Step 6: Conductor and Ground Braid Continuity (Required)

Schluter’s heating cables are protected by a ground braid. The electrical insulator prevents contact between the ground braid and the two conductors.

To ensure there’s no contact between the ground braid and two conductors, a continuity test must be done. Set the multimeter to test for continuity.

Place the black lead from the multimeter on the red wire and the red lead from the multimeter on the ground wire. If there is no continuity (meaning the test is successful) the reading on the multimeter should be either ‘OL’ for Overload or ‘I’ for Infinity.

Ground Braid Continuity

Do this same test for the black conductor in the heating cable. Place the black lead from the multimeter on the black wire and the red lead from the multimeter on the ground wire. Again, the reading on the multimeter should be ‘OL’ or ‘I’.

Ground Braid Continuity

If the test fails you won’t see either the ‘OL’ or ‘I’ on the multimeter.

In our case we did see the ‘OL’ and recorded the test result in the heating cable tests log.

 

Step 7: Insulation Resistance Test (Recommended)

This test will detect very small breaks in the cable insulation that were undetected during the continuity test.

Small breaks in the cable insulation can cause current leakage to ground. If this happens the current leakage will be detected by the GFCI and the GFCI will trip the circuit, thus disabling the DITRA-HEAT floor heating system.

NOT GOOD.

You’ll need a megohmeter (Mohm logo) to perform the insulation resistance test. Renting a megohmeter is your best option. Even Bill, our electrician, didn’t have one.

Place the black megohmeter lead on the ground braid and the red megohmeter on the red cable lead.

Insulation Resistance

Set the megohmeter range to 1000V and press the Test button. The megohmeter will inject 1000V into the heating cable and test for current leakage.

Test

Schluter recommends running this test three different times

  • Before the heating cable is installed in the membrane
  • After the heating cable is installed in the membrane
  • After the tile is installed on the membrane

The insulation resistance measurement must be equal to or greater than 1 Gigaohms (1 Gigaohms = 1 G ohms = 1000 M ohms = 1000 Mega ohms).

In our test we got 2200 M ohms and passed the test.

Passed Test

Do this test for the black lead on the heating cable as well.

Record the insulation resistance measurement in the heating cable tests log.

 

Step 8: Floor Temperature Sensor Test (Required)

The floor temperature sensors communicate the tile temperature to the thermostat. If they’re not working the thermostat won’t know when to turn the heat on and off.

So this test is very important.

You’ll get a sensor with the thermostat and a sensor with the heating cable. We mention this later in the tutorial, but you’ll only use one sensor and keep the other one in the electrical box as a backup.

Again, use a multimeter to verify accuracy of the sensors. Set the multimeter for resistance at 10K Ω +/- 2 (at room temperature) and take a reading between the sensor leads.

Clip one multimeter lead to the sensor’s red wire and the second multimeter lead to the blue wire in the sensor.

Sensor Test

The resistance will vary according to the temperature (i.e., the colder the sensor, the higher the resistance).

You can hold the sensor in your hand and test the resistance, the reading should be low because of the heat of your hand.

Hand Holding Sensor

Perform this test for both sensors.

Compare the measured values with the table of expected values and record in the heating cable tests log.

Sensor Test Log

 

Step 9: Heating Cable Cold Splice Installation

DITRA-HEAT heating cable is very straight forward.

But remember that cables should not be underneath a vanity. The minimum spacing is as follows

  • 2 inches from walls, partitions and fixed cabinets
  • 2 inches from toilet flanges (you’ll melt the was ring if closer!!)
  • 6 inches from floor drains
  • 8 inches from heat sources, e.g. baseboard heaters, forced air vents, fireplaces, etc.

We marked off the location of the vanity using blue painter’s tape.

Painter's Tape

Each heating cable will have a cold splice. This splice has to be set in the DITRA-HEAT membrane.

We recommend cutting out a portion of the membrane with a utility knife and using a chisel to cut out some of the subfloor, e.g. 1/8 of an inch.

Chisel Subfloor

Adhere the cold splice to the subfloor using either KERDI-FIX or a hot glue gun.

Hot Glue Cold Splice

The reason for doing this is the cold splice will interfere with the tile installation, i.e. the tile will be pitched upward due to the cold splice thickness. So having the cold splice flush with the DITRA-HEAT membrane is good.

 

Step 10: Heating Cable Installation in the Membrane

Heating cable should be no more or less than 3 studs apart.

Stud Spacing

Spacing closer than 3 inches may result in overheating and damage to the subfloor or surrounding structures. Spacing wider than 3 inches (4 studs) won’t provide enough power to heat the floor.

We ran our wire 3 studs from the wall and up to the blue tape of the vanity because the toe kick is indented three inches.

Vanity

The heating cable will snap into the DITRA-HEAT membrane studs. We used a grout float to help embed the heating cable.

Grout Float

And if you have a run of heating cable that’s more than 10 feet you’ll have to place a little loop or jog in the setup at that 10 foot mark.

Heating Cable Jog

The nice thing about DITRA-HEAT cables is the ability to customize the location and shape of the heating cable.

Customize Heating Cables

As you’re running the cable, keep that buffer zone in mind. For example, our buffer zone was a 6 stud spacing next to the tub.

Buffer to Tub

The buffer zone is basically the area for the last few feet of the heating cable.

As you can see in the picture below we also had a buffer zone next to the toilet.

Buffer to Toilet

 

Step 11: Thermostat Sensor Installation

Thermostat sensors should be placed evenly in between the heating cables. They should also be at least 24 inches from the wall without overlapping or crossing the heating cable.

Cut out a small sliver of a DITRA-HEAT membrane stud at a diagonal and snap the thermostat sensor into it. This will hold the sensor in the mat.

Diagonal Cut

The thermostat sensor wire is thinner than the heating cable, so it needs to be jogged every three studs.

Sensor Jog

We placed the backup thermostat sensor on the other side of the room.

Second Sensor

PRO TIP: Place the sensors in areas that don’t get direct sunlight as this will cause the sensor to misread the temperature in the room. Also, if you have a pet that likes to sit in a certain spot, don’t place the sensor there either!!

 

Step 12: DITRA-HEAT Thermostat Installation 

Before installing the thermostat re-test the heating cable by doing the conductor resistance test.

Conduct Resistance Test

Also, perform the floor temperature sensor test for both sensors.

Sensor Test

The DITRA-HEAT thermostat has a built-in GFCI. As such, there are LINE and LOAD terminals on the back of it.

GFCI Protection

L1 (Line 1) will receive your black wire from the electrical panel. Slide the black wire behind the L1 terminal screw and tighten it with a flat head screwdriver.

Hot Wire

L2 (Line 2) will receive the white neutral wire from the electrical panel. Slide the white wire behind the L2 terminal screw and tighten it with a flat head screwdriver.

Neutral Wire

PRO TIP: Only 1/2 inch of bare copper wire should be exposed on the hot and neutral wires, this prevents shorting out in the electrical box in case a ground wire is touching the hot or neutral.

Slide the black wires from the heating cable into one load terminal and the red wires from the heating cable into the other load terminal.

Heating Cable Wires

Use a wire nut to combine all the ground wires. Bill shows step-by-step how to do all the wiring in our video.

There’s an oval shape slot at the top of the thermostat.

Slot for Sensor

Slide one of the thermostat sensor wires through that slot and tuck away the other thermostat sensor wire. Make sure the wires don’t touch the terminal screws on the thermostat.

Also, don’t forget to snap the plastic guard onto the thermostat. It covers the terminal screws.

Bill used a 22.0 cubic inch electrical box for this project. Primarily because there are a lot of wires that need to fit in the box.

Push the thermostat into the box and ensure it’s right side up…the words should be readable on the thermostat!!!

Thermostat Words

Double check the ground wires aren’t touching any terminal screws. The last thing you need at this point is a short that ruins the thermostat!!

Screw the thermostat to the electrical box.

Place the sensor blue wire in the ‘C’ terminal and the sensor red wire in ‘D’ terminal.

Sensor Wired

Position the thermostat face onto the body and secure it by tightening the screw on the bottom.

Thermostat

PRO TIP: Since the thermostat has a GFCI you should test it monthly by pressing the Test button on the top of the Thermostat housing.

 

Step 13: Watch Our Step-by-Step Video

The last step for DITRA-HEAT installation is to fill all the studs with unmodified thin-set.

Thinset DITRA-HEAT Studs

If you have extra modified thin-set from the membrane installation you can use that to fill in the studs. But, the modified thin-set has to dry over night.

Furthermore, if you want to waterproof the entire floor, use the KERDI-BAND at drywall and DITRA-HEAT membrane transitions.

Watch our complete DITRA-HEAT installation video to see all the details.

DITRA-HEAT Heated Flooring Systems

 

What’s Next

We hope our tutorial helps you with your project.

If you’re remodeling a bathroom you might like our free ‘Guide to a Bathroom Makeover in 10-Days’, it has a ton of great tips

Get Our Guide

Thanks as always for reading, watching and being part of our community.

Have a great day and talk to you soon,

Jeff Patterson

 

 

 

 

P.S. If you didn’t know, we have online classes for homeowners doing a DIY bathroom remodel.

They’re affordable, step-by-step and awesome for newbies.

Learn More

8 Comments
  1. Shawn says:

    Great tutorial, Jeff! Cannot wait to get started. The electrical hookup was extremely detailed and helpful.

    1. Awesome Shawn, yah the electrical is easier when Bill’s show how to do it. The membrane is just like DITRA and very simple to install. Schluter does make a DITRA-HEAT trowel, I forgot to mention that in the tutorial. Keep me posted on your project, can’t wait to see the results.

  2. Debbie says:

    Great tutorial. Lots of detail.
    But one question left. I’m re-modelling my master bathroom. My whole house is tiled (not heated). When I re-do the bathroom floor will it be thicker / higher than the existing tile floor in the bedroom? If so – how much higher?

    1. Hi Debbie, great question. It’s hard to say how much higher the new tile will be but Schluter makes transition profiles that will help with that. DITRA-HEAT is 1/4 inch thick and the thin-set under it will take up about 3/16 of an inch. Then you have another 3/16″ of thin-set for the tile if it’s 1/4 inch thick. So that might help with the rough thickness of the new tile floor.

  3. Sarah Noggle says:

    Jeff,
    Thanks for a great tutorial! Which showed us we WON’T be doing this ourselves! Not a project that we can tackle on a large master bath area. Now I know what SHOULD be done & what to look for with my installation.

    1. You could definitely do it Sarah, it just takes attention to detail. And if you follow our directions and Schluter’s handbook you’ll be in good shape. That said, now you know the details involved and can watch to make sure the DITRA-HEAT is installed correctly.

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