Can you put underfloor heating under carpet without screed?

Why most underfloor heating cannot go under carpet

One of the biggest misconceptions about underfloor heating is that every system is installed the same way. It is not.

Traditional water underfloor heating runs pipes carrying warm water beneath the floor. Those pipes normally sit inside screed, or in a routed overlay panel system, which creates a much deeper floor construction than the heating element on its own. Many electric cable systems are also embedded in screed, tile adhesive or self-levelling compound, depending on the system and the flooring.

Those systems can heat a room perfectly well when they are designed and installed properly. The problem is what they do to your floor height, and what they cost to run.

The difficulty comes when you want underfloor heating beneath carpet in a house that already exists, and you do not want to dig up the floor, lose a significant amount of height, or bring wet trades into the room.

How the Ribbon is different

The EkoBuild Ribbon is 1.8mm thick. It is taped down with EkoBuild's own high-tech tape, over suitable insulation. We use Therm-All, which is 6mm Therm-All, which is acoustic, thermal and a 1000-gauge DPM in one.

Over the Ribbon goes a 0.8 tog rubber underlay rated for underfloor heating, and then your carpet.

There is no screed. There is no self-levelling compound. There is no overboard. And there is no waiting for a wet layer to dry before the carpet can be fitted. Once the system has been installed, connected and tested, the flooring goes down.

That is what makes it useful in a renovation, or in a room that is already finished, where you do not want to raise the floor or turn a heating upgrade into a building project.

What the finished floor build-up comes to

The tog rule, and the thing people get wrong

The carpet and the underlay both have to let enough heat through. Both have a tog rating, which is simply how strongly a material resists the movement of heat. Stack up too much of it and the warmth stays under the carpet instead of coming into the room.

The rule is a combined carpet and underlay tog of 2.8, no higher.

Here is the part most people get wrong. They assume a thick carpet is the problem. It is the weave of the carpet that sets the tog, not the thickness, so ask for the tog certificate before you buy

A compatible carpet over a heating rated underlay lets the warmth travel into the room far more effectively than a thick, spongy build-up ever will.

Can it be the room's main heating, or is it just a warm floor?

This is the real question, and it is the one that separates the Ribbon from a comfort product.

The Ribbon runs at 150W per m². When it is being designed as the primary heating for a room it needs to cover at least 70% of the available floor area, and 80% or more is better.

That means you are not putting one small warm section beneath your feet. You are using the available floor to create a large heat source capable of warming the room above it.

Below 70% it is a supplementary heat source, and we spec an infrared panel to make up the gap

The property, the insulation and the flooring still have to be suitable. But the system itself is designed to do more than take the chill off.

How quickly warmth comes through carpet

The Ribbon itself starts producing heat in about 3 minutes. Through carpet you will normally start to feel it in about 5 minutes.

Those are observations from our own installations, not guaranteed times. The insulation, the subfloor, the carpet you chose and the starting room temperature all make a difference.

It is also worth being clear about what that figure means. It is when warmth begins coming through the floor. It does not mean the whole room has come up to temperature in five minutes.

Getting the controls right

A room thermostat controls the temperature you want in the room. A floor sensor watches the floor itself and keeps it inside its permitted range. The floor sensor sits between two Ribbon runs, never on top of one

The thermostat goes 1.2 to 1.5m above the subfloor, in the room it controls.

The final 240V connection must be made by a Part P qualified electrician and certified to BS 7671. Everything up to that point is genuinely DIY friendly.

What actually goes wrong under carpet

From the installations we have seen, problems beneath carpet almost always trace back to one of these. They are not evidence that carpet and underfloor heating are incompatible.

• An unsuitable carpet or underlay, so the heat never reaches the room.
• Too little floor covered, so the system is fighting the room instead of heating it.
• Gripper rods nailed through the heating. Plan the Ribbon to stop short of the gripper line on every wall, and tell your carpet fitter the floor is heated.
• Controls installed in the wrong place, or the floor sensor sitting on top of a run rather than between two.
• Never put additional insulation, Kingspan, foam, beanbags or a mattress on top of the Ribbon. The heat has to escape upward. Trap it and the element keeps climbing

Underfloor heating under carpet FAQs