Electric Underfloor Heating as a Primary Heat Source

The "electric underfloor heating can't be primary" myth

Electric underfloor heating may provide floor warming or primary heating. The answer for your room depends on usable installed output, permitted floor temperature and calculated heat loss.

The important distinction is whether the installed system is designed to meet room heat loss. Cable, water and ribbon systems can provide primary heating when appropriately specified. Product type alone does not establish that.

How ribbon heating is designed

Cable mats use heating cable arranged across the floor. Some installations provide floor warming alongside another heat source; others are designed for primary heating. Check the rated output, fitted area and flooring limits against the room heat loss.

AHT Ribbon is a 1.8mm electric heating mat with a nominal output of 150W/m² of fitted mat. Choose whole stocked mats that fit the available floor, and check the complete floor construction, controls and room heat loss. Primary-heating suitability depends on usable output meeting the room’s heat loss.

Floor warming and primary heating are not the same thing

Decide whether the planned system needs to warm the floor or provide the room’s main heat before choosing a layout.

Floor warming is exactly what it sounds like. The system is installed to take the chill off a cold floor and make it more comfortable underfoot, while radiators or another system do the actual heating. You see it in individual bathrooms, kitchens and small areas. It is a comfort product, and its running cost depends on how both systems are controlled and the heat the room needs.

Primary heating has a much bigger job. It has to heat the floor, heat the room, and hold a comfortable temperature throughout the property. If the underfloor heating is doing that without radiators making up the difference, it is the primary heat source.

A system chosen for background warmth may cover too little usable floor area to meet the room’s heat loss. Primary heating needs a complete design that checks output, floor limits and room demand.

So the question to ask is not "does this house have underfloor heating?" It is: has this underfloor heating been designed to warm the floor, or has it been designed to heat the home?

Three things that decide whether it works

Even a system designed for primary heating can perform poorly if it is not installed correctly. Three things matter as much as the product.

The property. A well insulated house holds heat far better than a draughty, poorly insulated one. Insulation is not a detail here, it is half the job.

The amount of floor covered. Install too little heating and expect it to warm a large room, and it will struggle. That is what the coverage rule is for.

The complete installation. The insulation beneath the ribbon, the flooring above it, where the floor sensor sits and how the thermostat is set all change how the system performs.

If performance is poor, check the fitted output against room heat loss, insulation, floor suitability, controls and installation. The property, flooring and intended use need to be understood before choosing the system.

Coverage And Room Heat Loss

Whether the ribbon can be your only heat depends on room heat loss, installed output, flooring and controls. Coverage helps plan the layout, but a percentage cannot replace a heating design.

You do not heat under the kitchen units or the bath, so a real room rarely needs 100%. The free Room Designer works out your usable floor area and tells you the coverage your layout gives, so you can discuss the actual fitted area with your heating designer before deciding whether other heating can be removed.

Will it actually keep the room warm?

The system must be sized against the room’s calculated heat loss. The ribbon’s nominal output is 150W/m² of fitted mat; usable output also depends on the flooring, surface-temperature limits, insulation and controls. Confirm those details for your room.

Insulation is the part people skip and then complain about. Without it, a chunk of your heat sinks down into the subfloor instead of rising into the room. Choose insulation suited to the complete construction: Therm-All for suitable floating floors, or a specified rigid insulating or backer base for tile and stone. Confirm the installed output and room heat loss before relying on the ribbon as the only heating.

What it costs to run, the honest answer

Estimate running cost from your actual electricity tariff and a stated on-time assumption. Heat loss, floor construction and controls affect how long the system runs. Review these factors when comparing options.

• Insulation. Use insulation suited to the complete floor construction to reduce downward heat loss. Therm-All is intended for suitable floating-floor assemblies.
• Running cost depends on the fitted mat area, electricity tariff and actual thermostat on-time. At 150W/m², each square metre uses 0.15kWh for a full-power hour. Multiply that by your unit rate and measured or assumed on-time; an assumed duty cycle is a scenario, not a predicted bill.
• Smart scheduling. Set heating schedules on the touch screen thermostat to suit how you use each room. Actual on-time still depends on the selected temperature and the room’s heat loss.

Use the same room heat demand and clearly stated tariffs and on-time assumptions when comparing running-cost scenarios. Insulation and controls can affect demand and operation, but they do not guarantee a particular bill.

Pairing with solar and battery

Electric heating has one advantage gas never will: you can make the electricity yourself. Pair the ribbon with solar panels and a home battery and the maths changes.

Solar generation and a suitably sized battery may reduce grid imports, depending on the heating demand, available generation and tariff. Account for equipment cost, storage losses and the value of exported electricity; no near-zero heating bill is guaranteed. Read the solar guidance and battery-storage guidance, then confirm any separate specialist quotation, supply and installation arrangements. A Ribbon product estimate does not include a solar or battery installation.

Which rooms and floors suit it

Ribbon can be considered for primary heating where the usable output meets each room’s heat loss. Each floor finish also needs its approved construction:

• Compatible carpet and underlay, subject to the TOG limits, usable output and the room’s heat-loss assessment.
• Laminate and engineered wood
• Vinyl and LVT
• Stone and tile

Open-plan living rooms, kitchen-diners, bedrooms and bathrooms each need a suitable heating design and approved floor construction. Assess every room when planning a single floor or whole house. The mat is 1.8mm thick; insulation, support layers and the finish determine the complete height. If you are renovating and ripping up floors for a wet system is a non-starter, this is the version that fits. There is more on that in our guide to underfloor heating with no screed.

Losing the radiators

A correctly designed primary-heating system can free up wall space by replacing radiators. First confirm that the installed output meets the room’s heat loss at the permitted floor temperature; do not remove existing heating on the basis of a coverage percentage alone.

It also means one less system to maintain. No radiators, no rads to bleed, and on a full electric setup, no gas boiler and no annual service. The ribbon carries a manufacturer warranty, subject to AHT’s certificate, so the heat source you are trusting your whole room to is built to last.

How to size it for primary heat

Measure the room and exclusions, plan the whole mats that physically fit, and check the resulting output against room heat loss. The Room Designer provides the layout and stock estimate; a competent installer must check heating suitability and the electrical design.

• Map the room in the free Room Designer. It works out usable area, coverage and the whole-mat layout in a couple of minutes.
• Plan for 80%+ coverage where you can, especially in colder or north-facing rooms.
• Order the matching 1m Ribbon roll for open floors, and put insulation under it.

Want the full background on how the system works first? Start with our complete electric underfloor heating guide.

More of Russell's answers, including what it costs to run and how the four technologies compare, are on the answers page.

Related video

Watch the reviewed short clip and read its matching transcript. Use the current guidance on this page and the supplied product instructions for planning and fitting. Planning the heating layout: video, captions and transcript.

Electric underfloor heating as primary heat: FAQs