Floor Heating Installation Overview for Slab Heating

The amount of amperage draw depends upon how large the area is that you are heating. For coverage of areas less than 30 square feet, a 120V Slab Heat system will draw less than 6 amps. If you have a larger area over 180 square feet of heated space, then you will need a larger breaker plus additional controls. No matter what the size of the area you choose to heat, we recommend a dedicated circuit for your electric radiant floor heating system.

The Slab Heat radiant system adds no additional height. This is because it is embedded within the concrete pour.

The requirements are determined as follows: plan on 20 watts per square foot (at 3" spacing) without a floor covering; or 15 watts per square foot (at 5" spacing, cable only) with a floor covering. To calculate approximate power requirements, multiply the square feet by either 20 or 15 (per the above), and then divide by the voltage (120V or 240V) to arrive at Amps.

Yes — but the approach is different from new construction. You cannot embed cables into an existing cured slab, so there are two practical options for adding radiant heat to an existing concrete floor:

Option 1: Above-Slab Installation (Most Common)

Electric heating cables or mats are installed on top of the existing concrete slab, embedded in a thin layer of self-leveling underlayment or mortar before the finish floor is applied. This adds approximately ¼ to ½ inch to the floor height.

• Works under tile, stone, LVP, laminate, and engineered hardwood
• WarmlyYours TempZone™ Cable is ideal for this approach — it can be laid at custom spacing over any concrete surface
• An uncoupling membrane (such as Prodeso) can be used as the installation bed, adding crack isolation benefits

Option 2: Floating Floor System

A floating floor system with built-in heating (such as WarmlyYours Environ™ Flex Roll) can be installed over concrete without any mortar or self-leveling compound — ideal for renovation projects where minimal height gain is important.

Important: Insulate from Below

Existing slabs on grade often lack insulation beneath them. While you can't add under-slab insulation retroactively, using a thermal underlayment on top of the slab (such as WarmlyYours ThermalSheet) helps direct heat upward rather than losing it into the concrete mass.

Get a free SmartPlan™ or Instant Quote to find the best solution for your existing slab.

You should install the cable 2-3" below the finished surface, and attach it to rebar and/or reinforcing wire mesh to secure the cable in place.

The layers for the full installation are as follows:

• Bottom: 8-12” of compressed crushed rock aggregate (may already exist)
• 2” polystyrene insulation
• 2-3” layer of concrete
• Rebar and/or reinforcing mesh and attach the cable or mat
• Top: Pour a 2-3” layer of concrete as the final flooring surface

Call tech support at +1 (800) 875-5285 to customize this to your unique application.

Installing electric radiant heating in a concrete slab is done during the construction or renovation process, before the concrete is poured. Here is a step-by-step overview:

1. Prepare the subbase: Ensure the ground is properly compacted and a vapor barrier is in place. Add rigid foam insulation beneath the slab to prevent heat loss downward into the ground — this is critical for efficiency.
2. Lay rebar or wire mesh: The heating cable will be tied to this grid to hold it in position during the pour.
3. Install the heating cable: WarmlyYours electric heating cable is laid out in parallel runs at a consistent spacing (typically 3–4 inches apart for primary heat, wider for supplemental). Never cross or overlap cables.
4. Connect the cold leads: The non-heating lead wires are routed to the wall where the thermostat will be mounted.
5. Test the cable resistance: Before pouring, verify the cable resistance with a multimeter to confirm no damage has occurred. Record the reading.
6. Pour the concrete: The slab is poured carefully over the cables. Avoid dragging equipment directly over the cables.
7. Install the thermostat: Once the slab has cured (typically 28 days), connect the system to a WarmlyYours thermostat and commission the system.

Get a Custom Installation Plan

WarmlyYours provides a free SmartPlan™ — a professional layout drawn by our engineers showing exact cable placement, spacing, and wattage for your specific slab. You can also get an Instant Quote online in minutes.

In-slab radiant floor heating is an electric heating system where heating cables are embedded directly inside a concrete slab before it is poured. The cables become a permanent part of the slab, which then acts as a large thermal mass — absorbing heat and radiating it evenly upward into the room.

How It Works

1. Electric heating cables are laid out and secured to rebar or a wire mesh grid on top of the subbase
2. Concrete is poured over the cables, fully encasing them
3. Once cured, the slab is connected to a thermostat and powered on
4. The concrete heats up slowly and radiates warmth evenly across the entire floor surface

Key Benefits

• Even, consistent heat: No hot or cold spots — the entire slab surface radiates warmth uniformly
• Invisible system: No visible heating elements, vents, or radiators
• Long-lasting: Cables embedded in concrete are protected from damage and can last the lifetime of the building
• Ideal for new construction: Best installed during the initial pour of a new slab or addition

Not sure where to start? Request a free SmartPlan™ and our engineers will design a custom layout for your slab.

Any trade professional is qualified to layout slab heating cables and/or mats; electricians must make the electrical connections and test the wire; you can hire a concrete contractor to install the concrete for you.

You can control your slab heating system with any WarmlyYours nSpiration Series thermostat. Depending on the size of your project, you may also need to add a relay or nJoin power module.