Underfloor Heating Systems Explained

How underfloor heating works (the simple version)

A heat source warms water. That water is pumped through loops of pipe under the floor. The floor surface warms gently and heats the room mainly by radiation and gentle convection — a large area at a modest temperature, rather than a small hot radiator.

Key parts of a typical wet system:

• •Heat source — gas/oil/LPG boiler or air source heat pump
• •Manifold — distributes water to each loop; flow meters and actuators control zones
• •Pipe loops — continuous circuits in the floor (length and spacing matter)
• •Floor build-up — screed, boards or plates that hold the pipe and transfer heat
• •Controls — room thermostats, sometimes weather compensation from the heat source
• •Insulation below — so heat goes into the room, not the ground or the void

Water temperature is much lower than old radiator systems — often in the mid-30s to low-40s °C when designed for a heat pump, higher if a boiler is blended down at the manifold.

The main system families

Pipe in screed

The classic system: insulation on the slab, pipe clipped or on a carrier, then screed poured over. Once cured, the finished floor goes on top.

Strengths: strong thermal mass (steady heat), well-understood output, often competitive cost per m² when the floor is already open, excellent with heat pumps when designed properly.

Watch-outs: floor height build-up; dig-out if levels must change; drying and curing time before finishes. Traditional cement screeds are often discussed with a rough “1 mm per day” drying rule of thumb — a 65 mm pour is a long wait. Liquid screeds can be thinner and faster but still need a proper programme.

Best when the floor is open anyway (new build, extension, full renovation dig-out). Rarely the first choice if the family is living in the rooms day-to-day.

Overlay systems (gypsum, XPS and similar)

Designed for retrofit: a thin heated layer on top of an existing solid floor. Gypsum-type panels, XPS boards with pipe grooves, and mixed low-profile systems all sit in this family.

Strengths: less disruption, lower build-up, faster path to a finished floor, room-by-room phasing possible.

Watch-outs: the base must be sound and flat enough; finishes must match design assumptions; less mass than a thick screed (quicker response, less “flywheel”).

This is the system most occupied Devon and Cornwall renovations end up with on solid ground floors. Detail: overlay vs screed · UFH for renovations.

Joist and suspended-floor systems

Upper floors are usually timber. Options include aluminium heat-transfer plates between joists, overlays on the deck if height allows, and structural boards that replace the deck.

Critical details: plate contact with the deck, insulation in the void under the heated plane (so you heat the bedroom, not the ceiling below), and loop design for room heat loss.

Do not assume a wet screed belongs on ordinary domestic joists without structural design. Full guide: UFH upstairs renovation.

Electric underfloor heating — where it fits

Electric mats and cables are simple for a single bathroom or small zone. Running cost per unit of heat is higher than a heat-pump-driven wet system because you are using full-price electricity at 1:1, not a SCOP of 3+.

Fine as a local comfort product. Poor as a whole-house strategy if you are trying to cut bills and carbon with a heat pump.

Side-by-side comparison

Response times in more depth: not warming up fast enough.

Underfloor heating and heat pumps

They pair well because both prefer low water temperatures and steady operation. A large warm floor can deliver room comfort at flow temperatures a heat pump can produce efficiently.

What still has to be true:

• •Room heat loss calculated honestly
• •Pipe spacing and system type deliver enough output at that flow temperature
• •Floor finish matches design assumptions
• •Controls do not fight the system with deep setbacks

A boiler can drive UFH via blending at the manifold. If you are replacing plant anyway, heat pump + UFH is usually the cleaner long-term efficiency story. Related: heat pump and UFH — worth it?

Underfloor heating with a boiler

Modern boilers produce hotter water than UFH wants. The usual approach is a blending / mixing arrangement at the manifold so the floor sees a controlled lower temperature while radiators elsewhere (if any) can run hotter.

That works. It is slightly less elegant than a pure low-temperature heat-pump system, but it is common and reliable when commissioned properly.

Controls, zones and smart features

Most homes zone by room or area with thermostats and actuators on the manifold. That lets bedrooms run differently from living spaces.

Optional extras many homeowners ask about:

• •App / remote control and scheduling
• •Weather compensation from the heat source
• •Smart hubs (some brands need an extra gateway for full internet features)

Fancy controls do not fix a bad floor design. Get loops, insulation and balancing right first.

What affects cost

Homeowners often hear supply-only figures per m² and installed totals that look very different. Both can be honest — they measure different things.

• •System type — screed vs overlay vs structural boards
• •Area and number of zones — more manifolds and actuators cost more
• •Preparation — levelling, dig-out, joist access, insulation
• •Labour vs supply — installation can be a large share of the total
• •Finishes — not always in the UFH quote

Planning bands: UFH costs 2026 · use the UFH calculator for a project-shaped estimate.

How to choose (homeowner checklist)

1. Is the floor solid or joisted?
2. How much finished height can you spare at doors and stairs?
3. Are you living in the rooms during the works?
4. Is the heat source a boiler, heat pump, or still undecided?
5. Whole house or phased rooms?
6. What floor finish do you want (tile, timber, vinyl, carpet)?

Answer those before you fall in love with a brand name. Decision guide: best system for renovations.

Common problems (and where to read next)

• •Cold patches — balancing, air, coverings → cold spots guide
• •Feels slow — mass and setbacks vs real faults → not warming fast enough
• •Whole house cool on cold days — heat source capacity → heat pump “not heating” guides

Devon & Cornwall notes

• •Solid floors + low doors → overlay dominates retrofit
• •Mixed solid ground floor + joisted upstairs in one project is normal
• •Oil/LPG to heat pump switches make low-temperature UFH part of a bigger plan
• •Fabric still matters — UFH will not rescue an uninsulated solid-wall room on its own

Honest bottom line

Frequently asked questions