· by Michael Blair, Nashville's Tile and Stone
Electric radiant heat under bathroom tile is a small addition to a tile job and effectively impossible to retrofit without taking the floor up. That makes it a decision with a deadline, and it is worth understanding what it does and does not do before the tile setter arrives.
What it is actually for
Comfort rather than heating. A heated tile floor removes the specific unpleasantness of cold tile underfoot, which in an unheated Middle Tennessee bathroom over a vented crawl space is the coldest surface in the house on a January morning.
It can contribute meaningfully to warming a small bathroom, and it is generally not sized or intended to be the sole heat source for a room. Treating it as supplementary comfort heat sets the right expectation, and it is a very effective one at that job.
How it goes in
Either a cable laid out in loops and secured with strapping or a membrane, or a mat with the cable pre-spaced in a mesh that rolls out. The mat is faster and the loose cable adapts better to an awkward room shape, and both go under the tile in the thinset.
It is laid only where people stand, so it stops short of the area under a vanity, a tub or a toilet. Planning that layout properly against the fixture positions is what separates a good installation from one with a cold strip through the middle of the room.
- Decide before the tile job, never after
- Test the cable resistance before, during and after installation
- Keep the cable out from under fixtures and cabinets
- Requires a dedicated circuit with GFCI protection
- Uncoupling membranes and heat systems can often be combined
The electrical and permit side
A floor heating system needs its own circuit, sized to the load, with ground fault protection, and the thermostat has a floor sensor that must be run in a conduit sleeve so it can be replaced without demolishing the floor. Installers who omit that sleeve are creating a future problem.
This is permitted electrical work in Nashville, and it is normally handled alongside the rest of a bathroom remodel permit. It is also work where the value of an inspection is genuinely high, because the entire installation is about to be buried in mortar.
Running cost and control
These systems are resistance heaters, so their cost is straightforwardly the wattage multiplied by the hours they run. A bathroom floor is a small area and it does not run continuously, which is why the running cost is modest for what it delivers.
The control is what makes the difference. A programmable thermostat that warms the floor for the hour around when the household actually gets up costs a fraction of one left on all day, and it delivers the entire benefit. Most disappointment with running cost traces back to a system left in permanent operation.