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Instead of blowing hot air through a vent or pumping hot water to a baseboard radiator along the wall, in-floor radiant heat warms up the entire floor. The heat is made possible in two ways: either through pipes carrying hot water embedded in or directly below the floor, or via electric mats embedded in the floor.
This guide will show you how to install heated floors and covers the basic steps for installing electric mat radiant floor heat.
Types of Radiant Heat
Radiant heat supplied by hot water is called hydronic heating. Hot water is the standard for larger installations. It is generally more economical than electric heating. Because the flow of water can be minutely controlled, this system provides heat in the right amount exactly when and where you need it.
A hydronic radiant floor is no less complicated than a zoned-baseboard heat system. It uses a boiler heated by gas, oil or electricity, and requires valves and manifolds to distribute the water, as well as sophisticated thermostats to control the heat.
For under floor warming, electric radiant floor heat systems are installed directly over subflooring before the finished flooring. They are meant to be used as supplemental heat, so they are a good option for retrofits. Some wires are designed to double as thermostats, simplifying installation. You do not need to buy a separate furnace, so the initial cost is lower, and no pipes will freeze or spring leaks.
Electric radiant floor heat does require some planning and running a new circuit from the electric panel. If you are not comfortable adding a new circuit from the electric panel, hire an electrician to perform that task.
Where to Install
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.
Installing Underfloor Electric Radiant Heat
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 and Test the Mat
- 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.
Rough-In the Electrical
- 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.
Install the Mat
- 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.
Install the Controls
- 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.
Install the Flooring
- 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.
Now that you understand the basics of how to install heated floors, you can decide if a DIY heated floor a project for you.
When you're ready to find an electric radiant floor heat system and the tools you need, see The Home Depot mobile app to locate products and check inventory in your local store.
If you need help installing under floor heating, reach out to a professional. The Home Depot offers flooring installation services.