How to Install Floor Heating under Tile

How to Install Floor Heating under Tile

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Tools and materials required

  • Glue gun
  • Trowel
  • Utility knife
  • Volt-ohm meter
  • Cement board underlay
  • Cement board screws
  • Mesh fiberglass tape
  • Grout
  • Radiant heat mat
  • Thermostat
  • Thin-set mortar
  • Tile or other floor surface

Types of Radiant Heating Systems

Three different types of radiant heating systems are available for those interested in heated floors.

Forced-Air Radiant Heating

Air-heated radiant floors work by using a furnace to pump hot air through channels in the floor. This type of radiant heating has proven to not be cost-effective because air can’t effectively hold large quantities of heat, and is thus rarely used in homes.

Electric Radiant Heating

Electric radiant heating consists of either electric cables built directly into the flooring or electrically conductive mats installed between the subfloor and the floor covering.

Electric radiant heating is typically most cost-effective in the following two scenarios:

  • Your flooring has a significant thermal mass, and your utility provider offers time-of-use rates so that you can heat your flooring during off-peak hours (generally during the night). With a high enough thermal mass, your floor will retain the heat for eight to 10 hours without additional electricity. 
  • You are adding space to your home, and extending your current heating system into this new space would be impractical or expensive.

Hydronic Radiant Heating

Hydronic radiant heating systems are made up of a boiler and tubing laid under the floor in a specific pattern. Water heated by the boiler is pumped through the tubing to heat the flooring and, consequently, the room.

This type of radiant heating is the most cost-efficient and popular in areas that rely heavily on heating. Installation costs vary by installation type, home size, floor covering, location, and other factors.

With heated ceramic tile flooring, you can say goo
With heated ceramic tile flooring, you can say goodbye to cold bare feet.

3. Inspect the subfloor

Sweep the subfloor clean to make sure it is clear of any nails or other sharp objects that could damage the heating element (this applies to your floors and walls too). If your subfloor consists of a concrete slab, you will want to adhere cork or synthetic cork underlayment in a staggered pattern before beginning your floor-heating installation. If your subfloor is wood, underlayment is not necessary.

CeraZorb synthetic cork underlayment was installed
CeraZorb synthetic cork underlayment was installed under this TempZone Flex Roll to prevent heat from absorbing into the concrete subfloor.

5. Position the sensor

Some thermostats (like the Nest) only read ambient (or air) temperature, so a floor sensor is not required. However, if your floor-heating thermostat allows a floor sensor, make sure to position the sensor near the location of the thermostat and precisely in between two heating cables, being sure not to overlap them. To secure it in place, weave it into the mesh or use hot glue.

Whole-House Radiant Heating

Hydronic radiant floors are heated by warm water pumped through plastic tubing. Other components in a typical hydronic system include a boiler or water heater, a circulation pump, a manifold of valves to control water distribution, and a thermostat to control temperature. Due to size and complexity, most hydronic systems are installed by plumbers and/or HVAC contractors. The cost for an entire heating system ranges between $6 and $12 per square foot—two to three times the cost of other heating systems. However, a hydronic system offers substantial operational savings when used throughout the house, or at least over an entire level. At this scale, you can save around one-third over what you’d pay to heat by forced air. Carpet, tile, and vinyl flooring can go down over a hydronic masonry floor, although some efficiency is lost if you install a carpet pad. Tubing can also go down beneath a wood floor; it gets installed directly under the finish flooring or fastened to the underside of the subfloor, between joists (see illustrations). The joist-space option can work well in retrofit applications, provided you have access beneath the floor you want to heat.

Extra tips for Installing In-Floor Heating

Here are a couple of extra pro tips that will help you complete this project successfully.

Choose a different floor for the heated area

You can choose to heat a certain section of the floor only and then cover the whole floor in the same tiles. However, it is better to choose a different type of floor for the heated area, for example, a different type of tile.

This can create an attractive visual effect, but the main reason is that if something goes wrong, you will only have to tear up the section of floor that is heated rather than having to destroy the floor for the whole bathroom.

Tile or stone floors are best

When it comes to heated floors, the kind of materials commonly used in bathrooms are the best. Tile or stone floors conduct the heat perfectly, so when you step onto it barefoot in the middle of the night, it will be comfortably warm instead of unpleasantly cold.

Problems with Early Activation

As mentioned above, activating your new under tile floor heating system too soon, before the mortar has cured, can cause the grout to crack or to not adhere properly, and may void the warranty of your mortar product. In some testing, even the tile cracked when the system was run before the compound had cured. And mortar manufacturers may refuse warranty coverage if you do not follow their instructions. 

Some pros insist that turning on the floor heating system will help mortar cure faster or stronger, but we do not recommend this. We know of no reliable testing that proves this theory. Following your manufacturer’s instructions is the easiest and safest way to ensure your installation is a success. 

In fact, each manufacturer of products that Warm Your Floor sells offers tips on how long to wait before activating their traditional mat or cable systems: 

Schluter®-Systems: 

  • Wait 7 days after grouting before consistent use of the DITRA-HEAT system. Turning the system on briefly (e.g., 5 or 10 minutes) immediately after installation to check functionality is safe. 

Nuheat: 

  • Before activating the mats or cable, ensure the setting compound has fully cured. Refer to setting compound manufacturer’s specifications for cure times. 

Watts Radiant SunTouch: 

  • After all controls are installed, do not energize the system, except to briefly test operation of all components (no longer than 10 minutes). Do not put the system into full operation until the tile or flooring installer verifies all cement materials are fully cured (typically 2 to 4 weeks). See mortar manufacturer’s instructions for recommended curing time. 

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