Water-based underfloor heating systems are an excellent solution for providing comfort in both new buildings and older ones. This type of heating system uses warm water that flows through a network of pipes embedded in the floor, evenly heating the room from the bottom up. Heat distribution across the floor surface is consistent and comfortable, free from the hot and cold zones that radiators create. The way the system is installed, however, differs significantly between a new build and a retrofit, and that difference is the key to planning the project correctly.
Contents
- 1 Water-Based Underfloor Heating for New Buildings
- 2 Water-Based Underfloor Heating for Building Renovations
- 3 Main and Additional Components
- 4 Final Note
- 5 Frequently Asked Questions
- 5.1 Is underfloor heating cheaper to install in a new build or a retrofit?
- 5.2 How much floor height does wet underfloor heating add?
- 5.3 Can I retrofit water underfloor heating without lifting the whole floor?
- 5.4 What flow temperature should water underfloor heating run at?
- 5.5 What are the essential components of a water underfloor heating system?
Water-Based Underfloor Heating for New Buildings
Many people building new homes now prefer heat pumps as their energy source, and heat pumps are highly efficient when paired with water-based underfloor heating. The ideal low flow temperature for a heat pump is between 30 and 45°C, which is also perfect for underfloor heating. Although the system heats up more slowly than radiators, it retains heat longer and delivers steadier comfort. Under UK Building Regulations updated in 2025, new and substantially upgraded wet systems must be designed to operate at flow temperatures no higher than 55°C, which makes underfloor heating a natural fit for modern low-carbon homes.
The following is an overview of the steps for installation in a new building.
Installation Preparation
Wet underfloor heating is an ideal choice for new builds because it integrates easily with the screed stage, whereas electric mats can be simpler for small retrofits. Installers embed the warm water pipes into the screed after laying insulation and pressure-testing the circuits, before the floor is finished. A thermostat is then set in each room, providing both comfort and improved energy efficiency. The choice of floor covering, such as tiles or engineered wood, can further enhance heat transfer.
Insulation
This wet system follows the principle of neat installation, with screed used in tile areas where the pipes run underneath. This is typically suitable for the kitchen, living room, and bathroom. For wooden floors in bedrooms and living rooms, it is important to ensure proper insulation and a suitable wood type, such as engineered oak, typically 18 mm or less (always check supplier data). Insulation is crucial for reducing downward heat loss. Installers use high-quality floor insulation boards beneath the pipes across all areas, including both the ground floor and upper floors. For a detailed comparison of the options, see our guide on types of insulation boards for underfloor heating.
Control System
Water-based underfloor heating systems use smart zoning, with a thermostat installed in each room or zone. This allows independent temperature control in different rooms, and the control system can integrate with home automation for greater convenience.
Estimated Cost for New Builds
New build installations are the most cost-effective scenario for wet underfloor heating, because the pipework is laid before the screed without disturbing any existing structure. For 2026, UK supply and install costs for a new build wet system typically range from £70 to £100 per m², with straightforward, accessible sites reaching the lower end of that band. It is recommended to pair the system with a quality room thermostat for better control and efficiency; a smart thermostat for the whole house typically costs between £300 and £600. These figures reflect common UK market ranges in 2026, but actual prices vary depending on region, installer, and project specifications. Note that 0% VAT currently applies to energy-saving installations in the UK, which can reduce the total outlay.
Water-Based Underfloor Heating for Building Renovations
Implementing water-based underfloor heating in renovation projects requires careful planning. It is important to consider the condition of the existing floor and the available room height, since the main challenge in any retrofit is managing the additional floor build-up. The key considerations below address exactly that.
Floor Surface and Build-Up Height
Traditional wet heating systems require screed and insulation, which often means a total build-up of 50 to 100 mm (insulation plus screed). This added height can interfere with doors and skirting boards. As an alternative for retrofits, you can use a thinner surface build-up of 15 to 22 mm. In this case there is no need for a full screed. Instead, grooved or foil-faced boards designed for underfloor heating are laid directly over the existing floor. The final floor surface can be engineered wood, tiles, or vinyl, and the system simply connects to the existing heat pump or boiler. This low-profile setup is ideal for kitchens, bathrooms, and extensions undergoing renovation.
Board Selection
Accessing upper floors or finished areas for reinstallation can be challenging, and screed drying times can delay a project by several weeks even when fast-drying screeds are used. A practical solution for renovation projects is to use high-performance EPS boards with pre-formed pipe channels. These systems typically have a build-up of around 16 to 18 mm. Installation is quick, and they warm up faster than traditional screed underfloor heating. Once installed, you can lay tiles or position wood or vinyl flooring directly over the boards.
Estimated Cost for Retrofits
Retrofit installations cost more than new builds because the floor usually needs more preparation, levelling, and coordination with the existing structure. For 2026, UK retrofit costs vary by method. A low-profile overlay system (15 to 25 mm depth) typically ranges from £100 to £140 per m², while a full screed replacement retrofit ranges from £120 to £190 per m² due to demolition, screed replacement, and curing time. A suspended timber floor retrofit using spreader plates between joists typically falls between £85 and £130 per m². As with new builds, pairing the system with a quality thermostat is recommended, and 0% VAT on energy-saving installations applies. These are common UK 2026 ranges; actual prices depend on region, floor construction, and project complexity. For a deeper look at the factors involved, see our article on wet underfloor heating cost and installation considerations.
Main and Additional Components
When installing water-based underfloor heating, it is important to consider both the main and additional components.
Main Components
Plastic Pipes: Durable floor heating pipes are essential for carrying warm water throughout the system.
Manifold: The manifold distributes water evenly to each circuit and controls the temperature in each zone.
Insulation: Placed beneath the pipes, insulation prevents downward heat loss and ensures the system operates efficiently.
Floor Screed or Concrete Layer: This layer encases the pipes, helping to distribute heat evenly throughout the floor.
Additional Components
Thermostats and Control Panels: Room or zone thermostats, wiring centres, or smart control panels that let you set and monitor temperatures independently.
Edge Insulation Strips: Placed around the perimeter of rooms to prevent heat loss into walls and allow screed expansion.
Manifold Pump and Mixing Unit: If the heat source runs hotter than underfloor heating requires, a pump and blending valve may be fitted at the underfloor heating manifold to lower the flow temperature.
Expansion Joints and Fixings: Clips, rails, or staples for securing pipes, plus any necessary joints to accommodate screed movement.
“The single biggest mistake I see in retrofit underfloor heating is people not planning for floor build-up height early enough. In a new build, you have the whole screed depth to work with, so it is straightforward. In a retrofit, every millimeter matters. If you only realize at installation that a 70 mm screed system will not clear your doors, you have a serious problem. This is exactly why low-profile overlay boards exist. They let you add wet underfloor heating to an existing floor with as little as 15 to 18 mm of build-up. Knowing your height constraint before you choose the system saves the whole project from a costly redesign.”
— Maggie Shen, Founder of Legom
Final Note
These components work in conjunction with heat sources such as biomass boilers or renewable energy sources like air-source heat pumps to provide an efficient and sustainable heating solution. Whether you are building from scratch or upgrading an existing property, matching the system type to your floor construction and height constraints is the key to a comfortable, efficient result.
Frequently Asked Questions
Is underfloor heating cheaper to install in a new build or a retrofit?
A new build is significantly cheaper. Because the pipework can be laid before the screed without disturbing any existing structure, new build wet underfloor heating typically costs £70 to £100 per m² supplied and installed in the UK in 2026. Retrofits cost more, ranging from £100 to £140 per m² for a low-profile overlay system, and £120 to £190 per m² for a full screed replacement, because the existing floor needs preparation, levelling, and coordination. The cost difference comes almost entirely from the additional floor work that a retrofit requires, not from the heating components themselves.
How much floor height does wet underfloor heating add?
It depends on the system. A traditional screed system adds 50 to 100 mm of total build-up (insulation plus screed), which can interfere with doors and skirting boards. For retrofits where height is a constraint, low-profile overlay systems using grooved or foil-faced boards add only 15 to 22 mm, and high-performance EPS boards with pre-formed pipe channels typically add around 16 to 18 mm. Knowing your available floor height before selecting a system is essential, as it determines whether you need a full screed system or a low-profile alternative.
Can I retrofit water underfloor heating without lifting the whole floor?
Yes, in many cases. Low-profile overlay systems are designed specifically for this. Grooved or foil-faced boards, or EPS boards with pre-formed pipe channels, are laid directly over the existing floor with a build-up of around 15 to 18 mm, avoiding the excavation and full screed replacement that traditional retrofits require. The pipework connects to your existing heat pump or boiler, and the final floor finish (engineered wood, tiles, or vinyl) is laid over the boards. This approach is faster, warms up more quickly than screed systems, and is ideal for kitchens, bathrooms, and extensions.
What flow temperature should water underfloor heating run at?
Water-based underfloor heating typically runs at a flow temperature between 30 and 45°C, which is much lower than the 60 to 80°C of a radiator system. This low temperature is what makes underfloor heating so efficient, particularly when paired with a heat pump, which performs far better at lower flow temperatures. Under UK Building Regulations updated in 2025, new and substantially upgraded wet systems must be designed to operate at no more than 55°C, reinforcing underfloor heating as an ideal match for heat pumps and other low-carbon heat sources.
What are the essential components of a water underfloor heating system?
The main components are the floor heating pipes that carry warm water, the manifold that distributes water to each loop and controls zone temperatures, insulation beneath the pipes to prevent downward heat loss, and the screed or board layer that encases the pipes and spreads the heat. Additional components include room or zone thermostats and control panels, edge insulation strips around the room perimeter, a manifold pump and mixing unit to lower the flow temperature when the heat source runs hotter than required, and expansion joints and fixings to secure the pipes and accommodate screed movement. Each component plays a role in the system’s efficiency and reliability.
Reviewed and updated by the LEGOM Technical Team on June 27, 2026. This article covers water-based underfloor heating for both new builds and retrofits, including installation steps, insulation, control systems, floor build-up height, 2026 UK cost ranges, and the main system components, based on Legom’s experience as an underfloor heating component manufacturer supplying partners in more than 90 countries.