Heated Kitchen Floors: Electric Radiant Mats Under Tile and Other Floors

A warm floor is one of the small luxuries people most often say they are glad they added. It is also the upgrade with the least room for a late decision, because everything about it is buried under the finished floor. This page explains the two kinds of system, which floors can go over them, what controls them, and where the work falls in a remodel. If you have not chosen a floor yet, start with kitchen flooring options for Pacific Northwest homes.

Electric versus hydronic

Radiant floor heat comes in two forms. Electric systems run current through a resistance cable or mat that warms up. Hydronic systems pump warm water through tubing from a boiler or water heater.

For a kitchen remodel in an existing house, electric is the practical choice in nearly every case. The rest of this page is about electric systems. The permits a hydronic system touches are described in plumbing, mechanical and gas permits.

How an electric system goes together

The National Wood Flooring Association's installation guidelines describe several forms of electric radiant heat: heating cable carried on a mesh or fabric mat, loose cable held by straps or fixing strips, and thin heating films or foils made for floating floors. Under tile, the first two are the usual ones.

• Mats are cable pre-spaced on a mesh and rolled out. They are quick in simple rectangles.
• Loose cable is laid by hand, often snapped into a studded membrane, and weaves around islands and odd shapes.

Whichever is used, the cable is embedded in mortar or a self-leveling layer, and the tile is set on top. Over a concrete slab or an unheated crawl space, an insulating layer under the heat sends more of the warmth upward instead of into the ground.

Where the heat goes, and where it does not

Heat is laid only where feet go. It is kept out from under base cabinets, the island, the refrigerator and the range, for two reasons. Heat trapped under a fixed object has nowhere to go, and nobody stands there. That makes the heating layout dependent on the cabinet plan, down to the inch. In a typical kitchen the heated area is the aisles: in front of the sink, range and island, and the path through the room.

Which floor coverings work

Tile and stone

A heated tile floor warms and cools slightly with each cycle, which makes allowance for movement more important, not less. The Tile Council of North America recommends allowing for expansion and contraction in every tile installation and notes that movement joints are needed more often where a floor is exposed to moisture or direct sunlight. On a heated floor the perimeter gap and flexible sealant joints should be on the drawing.

Wood

Wood dries and shrinks as it is warmed, so it needs limits. The National Wood Flooring Association (NWFA) says that, unless the flooring manufacturer specifies otherwise, a radiant system under wood should be designed so the surface of the installed wood floor never exceeds 80 degrees Fahrenheit. Its guidelines add several points that shape the choice of product:

• Engineered wood is generally more dimensionally stable than solid, but not every engineered product is recommended over radiant heat.
• Engineered floors faced with less stable species such as hickory, beech and maple are not normally well suited unless the maker says so.
• Quartersawn and rift-sawn flooring is more stable in width than plainsawn, and narrow boards move less than wide ones.
• An electric system under wood must have a thermostat with an in-floor sensor, and the NWFA recommends one that limits floor temperature changes to 5 degrees Fahrenheit per day.
• Where two floor coverings share a system, each needs its own heating zone and thermostat.

Species and construction are discussed in hardwood floors in the kitchen.

Thermostat, sensor and circuit

An electric floor is controlled by its own wall thermostat connected to a temperature sensor embedded in the floor between two runs of cable. The thermostat reads the floor, not just the air, which is how it holds a comfortable surface temperature and enforces a cap for wood or vinyl. Three things to settle with your contractor:

• A schedule. Warming the floor before breakfast and resting it overnight is the main way to control running cost.
• A spare sensor. A second sensor set in the floor is inexpensive insurance, because a failed one cannot be reached later.
• Thermostat location. It needs a wall box and a wire path to the floor, chosen at design with the other switches.

The system needs a power supply sized by the electrician from the heating product's listing, and the electrical code has its own requirements for floor-heating circuits and their protection. We do not restate circuit sizes or protection rules here. Your electrician applies them, and the context is in kitchen electrical code in Washington.

Permits and inspection

Replacing a floor covering is finish work, but floor heat is electrical work. A new circuit, thermostat and heating cable need an electrical permit, and the wiring is inspected. Who issues that permit depends on whether the house is inside Vancouver city limits or elsewhere in Clark County, which is explained in electrical permits for kitchen remodels. The wider picture of what does and does not need a permit is in do you need a permit to remodel a kitchen.

Why it is planned before the tile

Floor heat touches four trades and has to be fitted between them in order:

1. Design. Cabinet and island positions are fixed, then the heated area, thermostat location and floor height are drawn.
2. Ordering. The mat or cable is ordered to fit. Cable cannot be shortened on site.
3. Electrical rough-in. The circuit and thermostat box go in while the walls are open.
4. Subfloor preparation. The floor is stiffened and flattened, and any insulation or membrane is installed.
5. Cable and testing. The cable is laid, and its resistance is tested and recorded before it is covered.
6. Embedding and tile. The cable is covered, tested again, and the tile is set.
7. Connection. After the mortar has cured for the time the makers require, the thermostat is connected.

What to check before you commit

• The heating product is listed by a recognized testing laboratory for the floor covering and installation method you plan.
• The flooring maker approves radiant heat, and states a maximum temperature if it is wood or vinyl.
• A drawn layout showing the heated area, cabinet and island edges, sensor position and thermostat.
• Insulation under the heat where the floor is over a slab or unheated space.
• Who makes the electrical connection and who holds the permit.
• Resistance tests recorded before, during and after embedding.
• Spare tile kept for any future repair.

Who should choose which

• A tile kitchen floor in a remodel: an electric mat or cable in the aisles. This is the common, sensible case.
• A wood kitchen floor: only with an engineered or stable-cut product approved for it and a floor-sensing thermostat with a temperature limit. Many wood floors are comfortable without heat.
• Vinyl plank: usually skip it. Vinyl is already warm underfoot, and the maker's temperature cap leaves little benefit. Limits are in luxury vinyl plank for kitchens.
• A whole-house gut or addition: the time to compare hydronic heat with your heating contractor.

JDI Construction draws floor heat into the kitchen plan with the cabinets, and handles the permits and inspections for the homeowner. To talk it through as part of a project, see our Vancouver kitchen remodeling page or contact us.