🧱What does electric underfloor heating cost to run?

In a bathroom, no — around $0.15 an hour for a typical 6 m² mat. Across a whole floor, yes: 40 m² at 150 W per m² is 6 kW, which costs about $1 an hour and can run to $1,500 over a winter. Electric underfloor is designed as a comfort layer for small rooms, not as the main heat source for a house.

Mats come at 100, 150 and 200 W per m². 150 is the standard choice for a tiled bathroom or kitchen, 100 for a room that only needs a warm floor rather than heating, and 200 for a conservatory, a poorly insulated floor or somewhere with a lot of glass. The number is the peak draw, not the average.

No — the thermostat cycles it. Once the floor is up to temperature the system runs perhaps 30 to 50% of the time to hold it, so the average over a heating period is well under the peak. The calculator uses hours at full power, which makes it a safe upper estimate; the first hour from cold is the one that really does draw everything.

To run, usually yes, because it is fed by a boiler or heat pump rather than resistance elements, and gas and heat-pump heat are both cheaper per kWh than direct electricity. To install, it is far more expensive and generally only makes sense during a build or a full renovation. Electric mats exist because they can go under a new tiled floor in a weekend.

For a small room, no — a programmable thermostat with two warm periods a day costs about half of continuous running. For a large slab with high thermal mass, a steady low setting can beat repeated reheating, because the slab takes hours to respond. The rule of thumb is that tile mats want scheduling and thick concrete slabs want stability.

A large one. Insulation boards under the mat stop heat going down into the slab, which typically cuts warm-up time by half and running cost by a fifth to a third. It is the cheapest part of the installation and the one most often skipped, and it is not something that can be added later without lifting the floor.