Introduction: DITRA-HEAT Heated Flooring Systems (Step-by-Step Installation)
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:
Membrane for DITRA-HEAT
Heating Cable for DITRA-HEATDITRA-HEAT Thermostat (Touchscreen) ($177)
KERDI-BAND ($28)KERDI-FIX ($25)
Modified Thin-Set ($40)
Unmodified Thin-Set ($25)
Trowel (1/4″x1/4″x1/4″ Square Notch)($14)
Utility Knife ($9-$11)
Rubber Float ($10)
5-Gallon Bucket ($3)
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.
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 cabinets2 inches from toilet flanges (you’ll melt the was ring if closer!!)6 inches from floor drains8 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).
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.
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.
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.
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. 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.Furthermore, we recommend getting a programmable thermostat.
Also, get KERDI-BAND to waterproof the seams of the DITRA-HEAT mats.
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.
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.
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.
Then mix the thin-set until it has a creamy smooth texture that’s slightly thinner than what you’d use for setting tile.
Dry fit the first sheet of membrane. Keep the DITRA-HEAT membrane a minimum of 1/8 to 1/4 inch from walls.
Cut membranes or mats using a utility knife.
If you use the roll it’s a good idea to counter roll it.
Counter rolling prevents the membrane from pulling up from the thin-set.
Clean the subfloor with a damp sponge and water.
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.
Go back over the burned thin-set with the trowel and this time make all the ridges the same direction, i.e. directional troweling.
Roll the membrane into the thin-set and embed it using a rubber or wood float.
Then pull back the membrane and check for 100% thin-set coverage on the fleece.
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.
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.
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.
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.
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.
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.
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.
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.
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’.
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.
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.
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.
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.
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.
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.
Perform this test for both sensors.
Compare the measured values with the table of expected values and record in the heating cable tests 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.
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.
Adhere the cold splice to the subfloor using either KERDI-FIX or a hot glue gun.
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.
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.
The heating cable will snap into the DITRA-HEAT membrane studs. We used a grout float to help embed the heating cable.
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.
The nice thing about DITRA-HEAT cables is the ability to customize the location and shape of the heating cable.
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.
The buffer zone is basically the area for the last few feet of the heating cable.
We also had a buffer zone next to the 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.
The thermostat sensor wire is thinner than the heating cable, so it needs to be jogged every three studs.
We placed the backup thermostat sensor on the other side of the room.
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.
Also, perform the floor temperature sensor test for both sensors.
The DITRA-HEAT thermostat has a built-in GFCI. As such, there are LINE and LOAD terminals on the back of it.
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.
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.
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.
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.
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!!!
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.
Position the thermostat face onto the body and secure it by tightening the screw on the bottom.
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.
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.
We hope you liked our tutorial.
If you want more bathroom remodeling tips check out our other Instrucables or visit us over at Home Repair Tutor.
Question 2 years ago on Step 12
Can anyone tell me what circuit breaker I should purchase for a 240v install? I am planning to buy a 15A breaker, I have installed them in the past, but I am used to using double pole 240v breakers for things like a kitchen stove. It has two different "hot" wires and one neutral. The thermostat only has a connection for a single hot wire and a neutral so I am a little confused about what breaker I should install for this project.
Answer 2 years ago
Haha! I found the answer to my question. If anyone else ever wonders about this you can find the answer here:
The answer is that you don't need the neutral wire in a 240v double pole thermostat connection UNLESS it specifically calls for one, which most do not. So that saves some money because I don't need to buy 12-3 or 10-3 wire. 12-2 or 10-2 wire is half the price. I do need a double pole 15A 240v breaker though.
3 years ago
Installed correctly, all tests came back fine ..will not heat over 74?
Reply 3 years ago
Same here but the temp never goes higher than 84 degrees even when i program the t-stat to the allowable 104 degrees for a bathroom tile floor.. Any ideas on why that is. It draws the proper 2.8 amps all day but stays at 84 degrees.
Question 3 years ago on Step 9
Not totally related. Were did you get your knee pads and who makes them? Can't find any like them. Walter
Question 5 years ago on Step 12
If the layout of tile and heated area requires more than one heating cable, I assume the programmable thermostat is capable of handling up to two cable connections as well as the sensor?
5 years ago
Do you realize this Instructable contains the words DITRA-HEAT 54 times?
I would have gone crazy typing it!