Wet or Electric Underfloor Heating: What It Means for Your Floor
How wet and electric underfloor heating differ for flooring choice, build height, response time and which floor coverings suit each system.
From a flooring point of view, the two systems behave completely differently. A wet system is a large, slow, powerful heat store buried in screed. An electric mat is a thin, fast, comparatively weak heat source sitting just below the surface.
That difference decides your build height, your adhesive, your tolerance for insulating layers and, in some cases, whether the floor you want is viable at all.
The two systems side by side
| Factor | Wet system | Electric mat |
|---|---|---|
| Build height added | 65 to 100mm with screed | 3 to 10mm with levelling compound |
| Response time | Two to six hours | 20 to 40 minutes |
| Output | High, can be the sole heat source | Modest, often comfort heat only |
| Tolerance of thick coverings | Better | Poor |
| Typical use | New builds, extensions, whole floors | Bathrooms, kitchens, retrofits |
| Suits carpet | Yes with low tog underlay | Rarely |
Floor coverings that suit a wet system
Glue-down LVT, engineered wood and tile all work well because they conduct rather than insulate and they sit in contact with the screed. Engineered wood is far safer than solid wood here, because its cross-bonded core moves much less as the floor cycles between warm and cool.
Click LVT and laminate can be used but need a compatible thermal underlay and a manufacturer that states a maximum surface temperature, usually 27 degrees.
Floor coverings that suit an electric mat
- Glue-down LVT set into the levelling compound over the mat, the most common choice
- Tile, which remains the natural partner for electric mats in bathrooms
- Thin sheet vinyl over a fully encapsulated mat, provided the adhesive is rated for the temperature
- Avoid carpet, thick laminate and floating floors with an air gap, all of which waste most of the output
Surface temperature limits are not optional
Nearly every resilient floor carries a maximum surface temperature, and 27 degrees is the usual figure. Exceeding it does not necessarily show on the day. It shows six months later as a shrunken joint, a lifted edge or an adhesive that has softened and let a tile creep.
A floor sensor set to limit surface temperature is the cheapest insurance available on a heated floor, and we would not fit LVT over a system without one.
Encapsulating the mat properly
An electric mat must be fully encapsulated in levelling compound before a resilient floor goes over it. Laying LVT directly onto the exposed cables leaves ridges that read through the tile and creates hot spots against the adhesive.
Allow for the cure time of the compound in your programme. It is usually a day, sometimes two on a thicker pour, and rushing it traps moisture under the finished floor.
Who decides the floor specification on site
On a heated floor the flooring contractor, the heating installer and the screeder all hold part of the answer, and problems nearly always occur in the gaps between them. The heating installer knows the flow temperature and the pipe layout, the screeder knows the depth and mix, and the flooring contractor knows the temperature limit of the covering.
Ask for the pipe layout drawing, the screed specification and the commissioning record before the floor is ordered. Those three documents between them tell you whether the floor you want is viable, what adhesive it needs and how long the drying programme has to be.
Where they cannot be produced, treat the floor as unknown and test it. A moisture reading and a thermal image of the pipe runs cost very little compared with lifting a bonded floor that has failed.
Retrofitting into an existing Kent house
In older housing stock with suspended timber floors, a wet system usually means lifting the boards and fitting between the joists with spreader plates, which is a substantial job. Electric mats over a ply overlay are far less disruptive and are what most retrofits end up using in bathrooms and kitchens.
In a ground floor extension with a new slab, a wet system is almost always the better long-term investment because it can heat the room on its own.
Costs to budget for the flooring side
On the flooring side of an underfloor heating project, the costs that catch people out are the levelling compound over an electric mat, typically £12 to £20 per square metre, the temperature-rated adhesive, which costs more than standard, and the floor sensor and limiting thermostat.
Allow for the programme too. Encapsulating a mat needs a day to cure, commissioning a wet system takes several days of gradual warm-up, and a new screed needs weeks or months. Flooring is the last trade in and it is the trade that absorbs everybody else's delays.
When we quote a heated floor we state the adhesive, the levelling method and the surface temperature limit on the quote, because those three lines are what protect the manufacturer's warranty if anything later goes wrong.
Frequently asked questions
- Can I put engineered wood over underfloor heating?
- Yes, and it is the recommended wood option. Keep the surface temperature to 27 degrees and let the boards acclimatise in the room first.
- Is solid wood ever suitable?
- Rarely. Solid boards move too much across the grain as the floor cycles, and gapping in winter is common.
- Do I need a different adhesive over heating?
- Yes. Use an adhesive rated for heated subfloors, and follow the manufacturer's open time, which shortens on a warm floor.
- How long before I can turn the heating on after fitting?
- Usually 48 hours, then raise the temperature in steps of around five degrees a day.
Keep reading
Which flooring types work well over underfloor heating, thermal considerations, and how commissioning affects fitting timescales.
Whether carpet can go over underfloor heating, the tog limits that matter, how underlay choice changes output, and when a hard floor is the better answer.
How latex self-levelling compound works, when it's needed, and how it differs from full sand-cement screed before new flooring.
See how we survey, prepare and fit LVT across Kent.
See how we survey, prepare and fit engineered wood across Kent.
Talk it through with a fitter, not a call centre
Book a free measure from our Gillingham warehouse and we will bring samples of the options discussed here, check the subfloor and leave you with a written quote you can hold us to.