Screed Systems
Thermal Conductivity and Underfloor Heating Suitability
An explanation of how a screed's thermal conductivity affects underfloor heating response time and overall system efficiency.
Designing a UFH floor and want screed advice?
Exeter Liquid Screeders can advise on screed type and thickness to suit your underfloor heating design.
Or call our landline on 01392 237700
Liquid screed is popular with underfloor heating designers largely because it achieves good, consistent contact with the pipe network and generally has a higher thermal conductivity than traditional sand-cement screed of similar thickness. This affects how quickly the floor responds to heat input and how evenly warmth spreads across the surface.
Thermal conductivity is a material property, expressed in W/mK, that describes how readily heat moves through the screed from the pipe network to the floor surface above. A more conductive screed transfers heat faster, which can allow lower flow temperatures for the same room comfort — relevant where heat pumps are the heat source and efficient low-temperature operation is a priority.
This isn't the only factor in UFH design — pipe spacing, floor covering, insulation below the screed and room heat loss all play a part — but screed choice is one of the levers available when trying to get the overall system to perform efficiently and respond predictably to demand.
Why contact with pipework matters
Traditional semi-dry screed can leave small air voids around pipework if not carefully compacted, which act as insulating pockets that reduce heat transfer locally. Fluid, pumped screed flows around the pipe network and settles under its own weight, generally achieving more even, void-free contact across the whole loop.
This consistency matters for even surface temperatures — cold or warm striping across a floor is often linked to inconsistent contact or spacing rather than a fault with the screed material itself.
Balancing conductivity with the rest of the design
A highly conductive screed won't compensate for undersized pipe spacing, excessive insulation resistance from thick carpet, or a poorly designed manifold layout — thermal conductivity is one input into a wider heat-loss and emitter calculation that a UFH designer should carry out for the whole property.
For heat pump installations in particular, getting the whole floor build-up right — insulation below, screed conductivity, and appropriate floor coverings above — supports lower flow temperatures and more efficient day-to-day running.
Comparing screed products by conductivity
Manufacturers publish thermal conductivity figures for their screed formulations, and these can vary between products even within the same binder family, depending on aggregate type, density and any additives used in the mix.
Where a project has specific efficiency targets, particularly with a heat pump as the heat source, comparing published conductivity figures alongside strength class and drying characteristics helps identify a screed that suits the whole design brief rather than one factor in isolation.
Response time and everyday control
Thinner screed above the pipe network generally responds faster to changes in heat input, which can suit rooms with more variable occupancy or heating patterns, while thicker screed with greater thermal mass tends to hold and release heat more gradually, evening out temperature swings over the day.
Zoning, thermostat placement and control strategy also interact with these response characteristics, so it's worth discussing expected day-to-day usage patterns with your heating designer alongside the screed specification itself.
Thermal Conductivity & UFH — the points that decide it
- Thermal conductivity (W/mK) describes how readily heat passes through the screed
- Fluid, self-levelling screeds typically achieve close, consistent contact around UFH pipework
- Higher conductivity can support lower design flow temperatures, useful with heat pump systems
- Floor coverings above the screed (tile, engineered wood, carpet) significantly affect overall heat transfer too
- Screed thickness above the pipe also influences response time — thinner screed generally reacts faster
- Manufacturer datasheets publish thermal conductivity figures for direct comparison between products
- UFH design should consider the whole floor build-up, not screed conductivity in isolation
- Pipe spacing and manifold design interact directly with screed conductivity in overall performance
- Void-free contact around pipework is as important as the conductivity figure itself
Thermal Conductivity & UFH — your questions
Designing a UFH floor and want screed advice?
Exeter Liquid Screeders can advise on screed type and thickness to suit your underfloor heating design.
Or call our landline on 01392 237700
In short
An explanation of how a screed's thermal conductivity affects underfloor heating response time and overall system efficiency.
Designing a UFH floor and want screed advice?
Exeter Liquid Screeders can advise on screed type and thickness to suit your underfloor heating design.