Planning underfloor heating for a new build or renovation can feel like stepping into a different language. Manifolds, actuators, thermal resistance… it’s enough to make anyone switch off before they’ve even started.
But here’s the truth: you don’t need to learn it all.
A working understanding of a few key terms can make a huge difference, helping you ask better questions, avoid costly misunderstandings, and feel confident that your system is designed properly from the ground up.
Think of this as your shortcut. A plain-English guide to the underfloor heating jargon that actually matters.
Underfloor Heating Jargon Explained: Know the Basics
Types of UFH Systems
Pipe in Screed system – a system where pipes are laid within a screed layer, using clips or a castellated tray to fix in place. This offers excellent heat output and even distribution and is the most popular UFH system for new-build and major renovations.
Overlay/Overfloor/Low Profile system – the term “overlay” is often used more generically, in relation to a system installed on top of an existing floor. In reality “Overlay” is actually the name of a specific brand of product. If you hear the terms “Overlay”, “Overfloor” or “Low Profile” they are typically referring to a panel-based system where the panels/boards lie on top of an existing floor. The systems are slim in their build up and are designed to minimise added floor height, making them ideal for retrofit projects. Insulated and non-insulated options are available.
Over-joist system – pipes are installed above the joists, usually within a pre-routed structural deck or overlay panels.
Between-joist system – pipes are fitted between existing joists, using routed insulated panels or metal grooved plates.
Most Commonly Used Terms
Heat Source – the appliance that provides the heat for your system, such as a boiler or heat pump.
Manifold – the central hub of your UFH system that distributes warm water to each loop of pipe and controls the flow.
Wiring Centre – the control box that connects all electrical components such as thermostats, actuators and the heat source, so they work together.
Actuator – a small, motorised valve on the manifold (one per port) that opens and closes to control water flow to each room based on thermostat demand.
MLCP – Multi Layer Composite Pipe, a flexible plastic pipe used in UFH systems, designed to handle heat and pressure while preventing oxygen from entering the system. “5 layer” is higher quality than “3 layer”, with or without an aluminium core, depending on UFH system type.
Subfloor – the structural base layer of your floor, such as concrete or timber, which everything else is built on top of. In newer properties, building regulations stipulate that subfloor includes insulation; often uninsulated in older properties.
DPM (Damp Proof Membrane) – a layer of plastic sheeting that prevents moisture from the ground rising up into your floor.
Vapour Barrier – a layer of thinner plastic that goes over your floor insulation and stops moisture from penetrating insulation.
Thermal Upstands – insulation placed around the edges of a room to reduce heat loss into the walls and allow the floor to expand slightly.
PIR – a rigid insulation board of varying thicknesses with excellent thermal performance, commonly used in new-build subfloors and beneath UFH pipes for pipe-in-screed systems.
EPS/XPS – types of polystyrene insulation; EPS is lighter and more cost-effective, while XPS is denser with greater moisture resistance.
Screed – a layer of material poured over UFH pipes to encase them, creating a thermal mass and leaving a smooth floor surface. There are many different screeds available depending on depth, required cure time and budget.
Datum Point – a fixed, established reference point (often a specific height marked on a wall, door frame, or a placed tripod) used to determine the exact, level height for the finished floor. It ensures the entire floor surface is perfectly level and at the correct height, commonly referred to as the Finished Floor Level.
Finished Floor Level (FFL) typically refers to the top surface of the structural floor (eg. concrete screed or timber) before final floor coverings (eg. carpet, tiles, vinyl, wood) are installed.
Levelling Compound – a thin, self-smoothing layer used to create a flat surface before the final floor finish is installed. Also used for remedial work to subfloors prior to UFH install when necessary.
Zone – an area of your home controlled by its own thermostat, allowing different rooms to be heated independently.
Loop – a continuous length of pipe that runs from the manifold, through a zone, and back again to circulate warm water.
Pipe Spacings or Centres – the distance between each pipe run on the design, calculated according to heat outputs required.
Serpentine / Concentric Layout – refers to the pipe layout design. Some systems, such as pipe-in-screed, can be laid to either design. Pipe design can impact heat consistency across a space.
Heated / Unheated Area – heated area is a space with UFH pipes installed, while an unheated area doesn’t (e.g beneath kitchen units). Remember with overlays, you still need a level floor throughout each room, regardless of heated/unheated areas.
CAD Design – a formal plan to which the system is installed, which shows every pipe loop to and from manifold. Also contains technical information for commissioning the system, such as flow and return temperatures, flow rates and heat outputs.
Thermal Resistance – a measure (m2 K/W) of how well a material resists heat flow. Lower resistance means better heat transfer into the room.
Tog Rating – a thermal resistance rating scale often used for floor coverings to show how much they insulate. Lower tog values are better for UFH performance.
Pressure Test – a check carried out before covering the pipes to ensure there are no leaks and the system is sealed properly.
System Commissioning – the process of setting up and testing the system to make sure it’s running efficiently and correctly after installation.
Bringing it all together
Underfloor heating might seem technical at first, but at its core it’s a simple idea: evenly distributing heat across your floor to create a more comfortable and usable living space.
Understanding the terminology just helps you see how all the pieces fit together, from what’s beneath your floor, to how heat is delivered and how each room is controlled.
At Cozia we work closely with homeowners to plan underfloor heating systems that don’t just tick the box on paper, but work beautifully with their homes in practice too. And we’re always very happy to demystify the process so you know exactly what you’re getting and why.
