Electric Underfloor Mat vs Wet Underfloor Heating

Frequently asked questions

Which is actually cheaper to run?

The wet system, in almost every case, and the size of the gap depends on two numbers from your own bills. Electric resistance heating converts electricity to heat with no loss, so its cost per unit of heat is simply the electricity price. A wet system's cost is the fuel price divided by the plant's efficiency — and for a heat pump that efficiency is three or four, so the same heat costs a quarter or a third of the electricity price even before any fuel price difference. Against a gas boiler the comparison is the gas price against the electricity price, which in most markets favours gas substantially. The mat wins only where the area is small enough that the difference is pocket change, which is exactly the bathroom-floor case it is good at.

Can an electric mat heat a whole room?

It can supply the heat, subject to the same floor surface temperature cap that limits any heated floor — and the question is whether you want to pay for it. A mat sized to meet a room's full heat loss is a resistance heater running for the whole heating season at the most expensive tariff in the house, and the annual cost is what surprises people rather than the capital. Where it genuinely makes sense as a primary source is a small, very well insulated room whose heat loss is trivial, or a space used so rarely that annual consumption is negligible. For anything larger, the honest recommendation is to treat the mat as the comfort layer and heat the room by other means.

Can I cut the mat to fit the room?

The MESH can be cut and turned; the heating CABLE must never be. Cutting the cable changes its resistance and therefore its output and its load, and in most products simply destroys it. The consequence is that the room has to be planned around the length supplied: you buy a mat whose area matches the free floor — excluding anything fitted, which does not need heating and would overheat if covered — and you lay out the turns so the whole cable goes down. If there is cable left over there is nowhere for it to go, and if there is floor left over it stays unheated. That inversion, planning the layout to consume exactly the cable supplied, is the single most useful thing to know before ordering one.

Which is right for a bathroom?

The mat, usually, and for reasons that have nothing to do with efficiency. A bathroom is small, so the running cost difference is modest in absolute terms; it is used in bursts, which suits a fast-responding system and defeats a slow screed; it is often being retiled with no room to raise the floor; and it is the room where a cold floor is most noticed. If the house already has a wet system and the bathroom is on it, extending the loops is obviously right. If it does not, running a wet system to one small room — manifold, pipework, commissioning — rarely justifies itself against a mat and a thermostat.

What thickness does each add?

The mat adds millimetres: the cable itself, a levelling compound or a flexible adhesive bed over it, and the tile. Total build-up above the substrate is commonly under ten millimetres plus the finish, which is why it can go into a retile with no change to thresholds. A wet system in screed adds tens of millimetres — pipe diameter plus the cover over it plus any insulation below — and a floating screed adds more again. Low-profile wet systems using grooved panels reduce that considerably and reduce the output with it, because there is less mass and less pipe per square metre. Where the floor level is fixed by an existing threshold or a stair, that dimension is frequently what decides the whole question.

Does either work well with solar generation?

The mat can use surplus generation directly, which is a genuine argument for it in a house with photovoltaics and no export payment worth having — resistance heating is the simplest possible way to turn surplus electricity into something useful, and a floor is a reasonable place to put it. The catch is timing: solar surplus peaks at midday in summer and heating demand peaks in the evening in winter, so the overlap is small in exactly the season that matters. A wet system on a heat pump uses that same surplus three or four times more effectively when it does coincide, and can store the heat in a cylinder or in the screed's mass. Neither makes solar a heating strategy on its own.

Does the floor covering matter?

It is one of the two things that decide whether the system works, and it is routinely decided last by somebody who was not told. Every heated floor is capped by a maximum surface temperature, so the heat reaching the room is limited by how much thermal resistance sits between the heat source and the air. Tile and stone are close to ideal — thin, conductive, and they let the floor deliver its full output. Engineered timber works within a limited thickness and with the manufacturer's blessing. Thick carpet with a foam underlay is the problem case: the combined resistance can halve the useful output, which turns an adequately sized system into an inadequate one without anything having failed. Decide the covering before sizing the system, not after.

What thermostat does each need?

Both need floor sensing, and for different reasons. An electric mat has no thermal mass and responds fast, so an air-sensing thermostat can overshoot the floor's surface limit badly before the room temperature catches up — the floor sensor is what protects the covering, the adhesive and the occupants' feet. A wet system needs its flow temperature controlled, ideally by weather compensation so the water is only as hot as the day requires, plus a floor limit and zone actuators driven by room thermostats. The commissioning consequence is real: a wet system set up as though it were a radiator circuit, with a fixed high flow temperature and a timer, throws away both the comfort and the efficiency that justified installing it.