Underfloor heating is one of those upgrades that, once experienced properly, is hard to give up. The warmth rises from the floor, the room heats evenly without hot spots near radiators or cold draughts at floor level, and there are no radiators taking up wall space. The comfort difference is real and meaningful. The question is whether it's appropriate for your project and your budget.
Wet Underfloor Heating
Wet underfloor heating (also called hydronic UFH) runs warm water through pipes embedded in the floor, connected to a manifold that distributes flow from a central heat source (boiler or heat pump). It's the heating system of choice in new builds across Scandinavia and Germany, and is increasingly common in UK extensions and renovations.
Why wet UFH pairs well with heat pumps. Heat pumps work best at low flow temperatures (35-45°C). Radiators sized for a traditional boiler (70-80°C flow) would be vastly undersized at heat pump temperatures. UFH operates naturally at 35-45°C, making it the ideal emitter for a heat pump installation. The combination of UFH and an ASHP is technically optimal: the heat pump runs efficiently, the floor distributes heat evenly, and the system design is integrated rather than compromised.
Floor build-up considerations. Wet UFH pipes are typically embedded in a screed (sand and cement, or liquid screed). A standard screed over UFH pipes is 65-75mm thick. This raises the floor level significantly. In an extension with a new slab, this is easily accommodated. In an existing house with suspended timber floors, the structural implications are more complex: the screed weight needs structural assessment, and the floor level change affects door frames, stairs, and thresholds.
Insulation beneath the pipes. UFH must have insulation beneath the pipes: standard minimum is 25mm PIR insulation in an extension on a new slab, more in Passivhaus applications. Without adequate floor insulation, heat goes downward as much as upward.
Response time. A wet UFH system in screed has a slow response time: it takes 30-60 minutes to warm up and several hours to cool down. This is actually an advantage (the floor acts as a thermal mass buffer) but requires a different approach to control: set-point thermostats and time schedules rather than rapid boost functions.
Electric Underfloor Heating
Electric UFH uses heating cables or mats laid in tile adhesive or thin self-levelling compound, directly under the floor finish. No screed is required: the system can be as thin as 3-4mm under tiles, or thinner still under floating floors using matting systems.
Where electric UFH makes sense:
- Bathroom and kitchen floor heating as a comfort supplement (not the primary heat source)
- Areas where wet UFH is impractical (existing suspended timber floors without access below, small areas where running pipework is disproportionate)
- Properties with solar panels: electric UFH can be timed to run on self-generated solar electricity, effectively using free energy
Running costs. Electric UFH running at grid electricity rates is significantly more expensive per kWh than wet UFH (which uses gas or heat pump efficiency). For a large area, the running cost difference over years is substantial. As a primary whole-house heating system in a standard property, electric UFH is expensive. As a floor comfort supplement in a bathroom powered by solar: a different calculation entirely.
For new extensions with concrete slabs, design wet UFH in from the start. The marginal cost of laying UFH pipes and manifold during slab construction is relatively low. Retrofitting wet UFH into an existing concrete floor requires breaking out the floor surface, which is expensive and disruptive.
Compatible Floor Finishes
Not all floor finishes are suitable over underfloor heating. The key criteria are thermal resistance and dimensional stability:
- Tiles (porcelain, ceramic, stone): Excellent. Good thermal conductivity, dimensionally stable. The most popular choice over UFH for both performance and aesthetics.
- Polished concrete: Excellent. High thermal mass, direct heat emission.
- Engineered wood: Compatible if the total thermal resistance (including the wood) is within the manufacturer's limits (typically total R-value below 0.15 m2K/W). Must be dimensionally stable: check that the specific product is approved for use over UFH.
- Solid wood: Generally problematic. Solid timber is dimensionally unstable with temperature cycling and can cup or gap. Not recommended over wet UFH.
- Vinyl and LVT: Most products are compatible; check manufacturer specification for UFH approval and maximum floor surface temperature.
- Carpet: Significantly reduces UFH efficiency due to high thermal resistance. If used, specify low-tog carpet and underlay (combined tog rating under 1.5).
Installation Costs
Wet UFH in a new extension ground floor slab (materials and installation):
| Area | Approximate cost (2025) |
|---|---|
| 20m2 extension | £1,800 - £3,200 |
| 40m2 open plan ground floor | £3,200 - £5,500 |
| Whole house ground floor (100m2) | £7,000 - £12,000 |
Electric UFH (bathroom, 5m2): £300-£600 materials installed. Larger areas proportionally more.
These costs cover the UFH system but not the screed, which is a separate cost (£25-£45 per m2 for liquid screed in most areas).