Radiant Heat Under Tile: What to Know Before You Install

Blog — February 9, 2026

Electric vs. hydronic

Electric radiant mats are the more common retrofit for a single bathroom — they install directly under the tile with a simple thermostat. Hydronic (water-based) systems tie into the home's boiler and heat larger areas more efficiently, but they're a bigger job to add after the fact. Most of our bathroom remodels use electric; whole-home projects sometimes bring in hydronic during framing.

Substrate prep is the part that gets skipped

A radiant mat installed directly on subfloor without an uncoupling membrane transmits every seasonal movement straight into the tile. We install a membrane system (typically Schluter Ditra-Heat) that isolates the tile from substrate movement and holds the heating cable in place — it also acts as a vapor barrier.

Sizing the system to the room

Heating cable spacing and wattage should be calculated for the specific room, not assumed. Too little coverage near an exterior wall or window leaves cold spots; too much drives up the electric bill for marginal comfort gain.

What it costs to run

For a typical primary bathroom, an electric radiant floor on a programmable thermostat adds a modest amount to a monthly electric bill when used on a timer for morning and evening — most homeowners find it worth it after the first winter.

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