How to Install Heated Floors

Hydronic radiant heat systems can be installed either above or below the subfloor. Electric radiant floor heat is installed over the subfloor, so the heat source is heating up the flooring and not the subfloor.

In a retrofit, this can raise the floor an inch or so, depending on the manufacturer, so be sure to plan for the thickness increase at door transitions and around appliances. 

Electric radiant heating works best under tile floors. DIY radiant floor heating can be installed under vinyl, engineered flooring and wood floors as well – though be sure to read the manufacturer’s guidelines. Its success with carpeted floors depends on the length of the weave – thick carpets or those with thick pads won’t work well as heat generated by the system will stay trapped in the floor.

There are two basic types of electric radiant heat systems: loose cable and mats embedded with cable. Loose cable systems come in spooled cable that are pre-cut from the factory. Lengths vary based on the square footage they cover. Installing loose cable systems can be tricky. While the cable can be routed in a variety of configurations, attaching it to the subfloor requires care and attention.

Mats, however, are easy to install and wire. They are comprised of mesh or fiber mats with cable embedded in them. They can be attached through the mat and not the wire, making them easier to run. Both loose cable and mats made for above-the-floor installation need to be covered with a layer of mortar for protection.

Before installing in floor heating, check with an electrician to be sure your existing electrical system can handle the new circuit, if it needs one. In general, you will need between 8 and 12 watts per square foot of heated floor.

• Inspect the mat, control and sensor for any visible damage.
• Use a digital multimeter to measure the resistance between the conductors of the mat power leads per the manufacturer’s instructions and specifications. 

• Be sure to refer to all local building and electrical codes prior to heated floor installation. 
• Depending on the manufacturer’s specifications, it may be necessary to run a dedicated electrical circuit to power the electric radiant heating system. Some systems can be run off an existing circuit if there is adequate power available. 
• Some electric radiant systems have integral GFCI protection, others require GFCI or AFCI protection from circuit breaker. 
• Install an electrical box for the system control unit (on/off switch, thermostat, or timer). 
• Drill holes in the bottom plate per the manufacturer’s instructions. Typically, this will mean drilling two holes into the bottom plate directly below the system control box. One hole will be used for the power lead from the mesh, and the other will be for the thermostat sensor. 
• Install the appropriate 12 or 14 AWG feed wire from the breaker or circuit you are tapping for power to the electrical box. 

• As you continue installing in floor heating, sweep or vacuum the subfloor so that it is free of all dirt and debris. Inspect the subfloor to make sure there are no screws, nails or other items that may damage the cable. 
• Place the mat on the floor so that the power lead can reach the electrical box. 
• Next, test fit the mat. Roll out the mat, flipping it over itself to turn as needed. 
• It is important to note that the heating wire cannot be cut and it cannot be routed into the wall, under baseboards, etc – all heating wire has to be embedded in the floor mortar. 
• Refer to the manufacturer’s guidelines for exact routing guidance for the mat. Typically, this will include keeping it 4”-6” away from walls, showers, tubs, etc – and 6” away from the toilet wax ring. Be sure the heating wire will not end up under any finish trim like door casings or baseboards. 
• Secure the mat to the floor using double sided tape, hot glue, or pneumatic staples. If using staples, be sure to stay more than ¼-inch from the heating wire. 
• Repeat step 1 above using a digital multimeter to measure the resistance between the conductors. 
• Feed the power lead and temperature sensor wire to the electrical box. A fish tape may be needed to run the wires behind finished wall surfaces. 
• Chisel a notch in the floor to recess the factory splice so that it does not stick up beyond the top of the rest of the mesh. 
• Install a metal nail plate across the holes in the bottom plate to protect them from stray nails. 
• Once the electric mat is secure, it’s a good idea to take photos of the system. 

• Ensure that power is off to the feed wire you installed in step 2. 
• Connect the power lead from the heating mat to the feed wire. 
• Connect the floor heating thermostat and controls to the wire per the manufacturer’s instructions.

Note: Do not turn on power to the system except to test it briefly. Follow the manufacturer’s guidance for testing the system. 

• If installing tile, use a polymer-modified thinset directly over the mat. Take care not to damage the wire when spreading the thinset with a trowel.
• If installing laminates, hardwood, or carpets, apply self-leveling compound over the mat. 

Note: No matter what kind of floor covering you choose, the heating mat must be fully encapsulated in a mortar bed.