The two types of underfloor heating
When it comes to underfloor heating (UFH), there are two distinct systems to choose from: wet (hydronic or water-fed) and dry (electric). Understanding the difference between the two is essential before specifying your screed installation.
Wet underfloor heating circulates hot water through a network of pipework buried beneath the floor. That water is heated by your boiler or, increasingly, by an air source or ground source heat pump. The pipework connects to a manifold, which controls the flow to different zones of the property. Because the water temperature can be set relatively low — typically 35–55°C — wet UFH is highly compatible with heat pump technology and represents the most energy-efficient whole-house heating solution available.
Dry (electric) underfloor heating uses resistance cables or heating mats to generate heat directly. These systems are simpler to install and do not require pipework, a manifold or modifications to your plumbing. For whole-house heating, electric UFH carries a significantly higher running cost than wet. However, for single-room applications or retrofits where installing pipework is not practical, it remains a compelling and cost-effective option.
Which underfloor heating system works best with liquid screed?
Both wet and electric underfloor heating can be successfully installed beneath liquid screed, but the two systems interact with screed differently — and that distinction matters for performance.
Wet UFH is the primary combination. When liquid anhydrite or Cemfloor screed is poured over wet UFH pipework, it flows around and beneath the pipes completely, eliminating air gaps that reduce thermal efficiency in traditional sand and cement installations. The result is exceptional thermal contact and superior heat transfer directly from pipe to floor surface. This is why liquid screed and wet UFH are consistently specified together on new build projects across London and the South East.
Electric UFH mats can also be encapsulated in screed, typically using a thin latex screed for retrofit applications where floor build-up depth is limited. This approach is particularly useful in kitchen and bathroom renovations where a full anhydrite pour is not warranted. For full guidance on how UFH and screed interact, see our underfloor heating guide.
Wet underfloor heating with liquid screed — costs and efficiency
Wet UFH carries a higher upfront installation cost than electric. Pipework, manifolds, pump sets, zone valves and the labour to install them all contribute to that figure. However, the long-term running cost picture is substantially more favourable, particularly when a heat pump is specified alongside the system.
A modern air source heat pump operating with underfloor heating can achieve a Seasonal Coefficient of Performance (SCOP) of 3.0 to 4.5 or better — meaning for every unit of electricity consumed, you get three to four-and-a-half units of usable heat. Compare this to a gas boiler, which operates below 1.0 SCOP, and the energy savings compound significantly over time.
The Government’s Boiler Upgrade Scheme (BUS) currently provides grants of up to £7,500 towards the cost of installing an air source heat pump, making the financial case for wet UFH with a heat pump considerably stronger. See our liquid screed cost guide for typical screed pricing in London.
Liquid screed provides significant thermal mass in combination with wet UFH. This means the system takes longer to warm up initially — typically two to three hours — but once at temperature, it maintains heat with excellent evenness across the entire floor surface. This characteristic makes it ideal for open-plan ground floor spaces and new build properties where the system can be set on a programmed schedule.
Electric underfloor heating with liquid screed — when does it make sense?
Despite the higher running cost, electric UFH has clear advantages in specific scenarios. For a single-room addition — a new bathroom, a kitchen extension, or a home office conversion — installing a full wet system with pipework and manifold modifications is rarely cost-effective. Electric mats can be installed quickly, with minimal disruption, and brought to temperature within 30–60 minutes thanks to the reduced thermal mass in a thin-bed installation.
Electric UFH also makes sense for retrofits where the existing structure cannot accommodate the floor build-up required for a wet system. Using a latex screed, electric heating mats can be embedded in a total floor build-up as shallow as 10mm, making them suitable for renovation projects with tight height tolerances. For more detail on this application, see our latex screed page.
What screed depth do I need for underfloor heating?
Screed depth over UFH is not a matter of preference — it is a technical specification that must be followed to achieve the correct balance of thermal performance, structural integrity and manufacturer warranty compliance.
Over wet UFH pipework, the minimum screed depth is typically 50mm measured from the top of the pipe. For anhydrite (calcium sulphate) screed, including Cemfloor, this equates to a finished depth of approximately 65–75mm depending on pipe diameter. This depth ensures adequate encapsulation of the pipework and provides the thermal mass required for even heat distribution across the floor surface.
Over electric heating mats, the minimum screed depth is 40mm for a standard anhydrite or Cemfloor pour. Where floor build-up must be minimised, latex screed can be applied at 10–15mm total depth, provided the mat specification permits it — always confirm with the UFH manufacturer before proceeding.
Deeper screed increases thermal mass, which slows response time but improves temperature evenness. Always refer to your UFH manufacturer’s specification and consult our technical data page for product-specific guidance.
Commissioning underfloor heating after screed — the correct protocol
Commissioning UFH before the screed has adequately dried is one of the most common — and costly — mistakes made on new build and renovation projects. Done incorrectly, it causes cracking, surface failure and can void both the screed and UFH warranties.
The correct commissioning protocol for liquid screed over UFH is as follows. After the screed pour, allow a minimum of seven days before introducing any heat. On day seven, begin with the flow temperature set at 20–25°C and hold at that level for three days. After three days, increase the temperature in steps of no more than 5°C per day until the maximum operating temperature (55°C for anhydrite screed) is reached. Hold at maximum temperature for a further seven days. This process force-dries the screed and proves the UFH system before any floor coverings are installed.
Never exceed 55°C in an anhydrite screed installation. Never begin commissioning before day seven. Following this protocol correctly is a condition of most liquid screed product warranties. Full guidance is available in our underfloor heating guide.
Which underfloor heating system should I choose for my London project?
The right choice depends on your project type, budget and long-term energy goals. As a general rule: for a new build whole-house installation, specify wet UFH — and if your budget allows, pair it with a heat pump from the outset to maximise efficiency and take advantage of BUS grant funding. For a single-room addition or retrofit where pipework is impractical, electric UFH is the pragmatic solution.
If you are extending an existing UFH system — for example adding a new room to a house that already has wet UFH — match the existing system type to avoid manifold and boiler compatibility issues.
The most important principle is that your UFH supplier and your screed installer should be consulted together, not in isolation. The screed specification — depth, product type, curing protocol — must be matched to the UFH system from the outset. Getting this right at design stage costs nothing; correcting it after installation can cost thousands.
For expert advice on screed specification for your project, call us on 07730 584 748 or contact us online for a free quote.