Underfloor heating warms a room by turning the floor itself into a large, gentle radiator. It comes in two main forms: wet systems, which circulate warm water through pipes, and electric systems, which heat thin cables or mats laid under the floor finish. Both deliver heat from the ground up, spreading warmth across the whole floor area rather than from a single point on a wall.
What underfloor heating actually is
Underfloor heating, often shortened to UFH, is a method of heating a space using the floor as the emitter. Instead of relying on radiators that warm the air immediately around them, the entire floor surface becomes warm and releases heat steadily upwards.
Because the heated area is so large, the floor only needs to sit a few degrees above room temperature to keep a space comfortable. That low surface temperature is part of what makes the system feel even and unobtrusive.
The two families of system share that principle but reach it in different ways. A wet system uses water heated by a boiler or heat pump. An electric system uses electrical resistance to warm cables directly. Which one suits a room depends on the floor, the building, and how the space is used.
Wet versus electric systems
Underfloor heating warms a room by turning the floor itself into a large, gentle radiator.
Wet underfloor systems run warm water through a network of flexible pipes laid in loops beneath the floor. The water is typically heated to a lower temperature than a radiator circuit would use — often around 35 to 45°C rather than 60°C or more — which suits modern boilers and pairs especially well with heat pumps.
At the heart of a wet system sits the manifold. This is a metal unit, usually mounted on a wall in a cupboard or utility area, where the pipe loops connect. The manifold distributes warm water to each loop and lets the flow to individual rooms or zones be balanced and controlled. It is the point where the whole circuit is managed.
Electric underfloor heating uses cables or pre-spaced mats connected to the mains and governed by a thermostat. There is no manifold and no water, which keeps the installation simpler and the build-up thinner. The trade-off is running cost: electricity is more expensive per unit of heat than gas, so electric systems are generally chosen for smaller areas rather than whole-house heating.
In broad terms:
- Wet systems tend to suit whole houses, new builds, large open-plan spaces and homes with a heat pump.
- Electric systems tend to suit single rooms, bathrooms, en-suites and retrofits where lifting the floor by much is not practical.
Both can be the primary source of heat for a space, but electric is more often used as a comfort layer — warm tiles underfoot in a bathroom, for example — rather than the main heating for a large area.
How it heats a room evenly
The even feel of underfloor heating comes from physics. Heat rises, so warming the floor pushes a gentle, uniform body of warm air up through the room. There are no hot spots near a radiator and no cold corners far from one.
A large emitting surface at a low temperature also reduces the strong air currents that radiators create. Radiators heat the air directly beside them, which then rises quickly and circulates, often carrying dust with it. A warm floor produces a slower, steadier movement of air and a more consistent temperature from floor to ceiling.
This even distribution is why rooms with underfloor heating often feel comfortable at a slightly lower air temperature than they would with radiators. The warmth is where people actually are — at floor and seating level — rather than gathered near the ceiling.
Response time differs by system and by floor construction. A thin electric mat under tiles warms up quickly. A wet system set within a thick concrete screed warms slowly but holds its heat for a long time, which suits a steady, all-day temperature rather than rapid changes.
Retrofit realities and floor heights
The biggest practical question in any retrofit is the floor build-up — the total thickness of the layers that make up the finished floor. Adding underfloor heating adds layers, and that raises the floor level. In a new build this is planned for. In an existing home it has knock-on effects.
A traditional wet system is laid in a screed, a poured layer of cement-based material that covers the pipes. With a screed, the floor can rise by 65mm to 100mm or more once the insulation, pipes and screed are accounted for. That extra height has to go somewhere, which can mean adjusting door heights, skirting boards and the transition to adjoining rooms.
Low-profile and overlay systems exist to address this. These use grooved insulation panels or thin spreader plates that carry the pipework, building up by perhaps 15mm to 30mm rather than 100mm. They warm up faster than a deep screed but generally hold less heat.
Electric systems usually add the least height. A cable or mat plus the tile adhesive and finish may add only 10mm to 20mm, which is why electric is common in bathroom and kitchen refurbishments where the floor is coming up anyway.
A few things are worth checking before assuming underfloor heating will fit an existing room:
- How much height can the floor gain before doors and stairs become a problem?
- What is the existing floor — suspended timber or solid concrete — as each calls for a different approach?
- Is there insulation below the heated layer, since heat lost downwards is wasted?
- What floor finish is planned, as tile and stone conduct heat well while thick carpet and underlay can insulate against it?
None of these rule out a retrofit, but together they shape which system is realistic. A whole-floor wet system in a room that cannot lose any height may be impractical, while a low-profile or electric solution may slot in with minimal disruption. The right choice balances the floor you have, the heat source available and how the room will be used.