Wet Underfloor Heating: UK Installation & Costs
Wet underfloor heating circulates warm water through pipes embedded in floor screed or a dry board system, powered by a gas boiler or heat pump, and is the standard choice for whole-house heating.
Wet UFH uses 16mm PE-X plastic pipes laid in loops in floor screed or a dry board system, connected to a boiler or heat pump via a manifold. Costs £80-150 per m² installed plus £800-1,500 for the manifold and pump. Runs at roughly 3-5p per kWh (gas) or 2-4p per kWh (heat pump, before efficiency losses), much cheaper than electric UFH. Best suited to whole-house or open-plan heating rather than a single small room.
How wet UFH works
Hot water from a boiler or heat pump flows through 16mm plastic (PE-X) pipes laid in loops across the floor area. Flow temperature runs at 35-45°C, noticeably lower than the 60-70°C typical of a radiator system, because the pipes are spread across the whole floor and don't need to run as hot to deliver the same heat output into the room.
Pipe spacing is typically 150-200mm apart in rooms with higher heat loss (bathrooms, rooms with lots of glazing) and can be spread wider, up to around 300mm, in well-insulated living areas with lower heat demand. The pipes are embedded in 50-75mm of screed in a traditional wet system, or set into grooved boards in a dry system.
A manifold controls each heating zone separately, so a living room, kitchen and bedroom can each have their own thermostat and run independently rather than the whole house heating on one schedule. A circulating pump moves water through the system, and a mixing valve at the manifold blends the boiler's hotter water down to the lower flow temperature the UFH pipes need.
Pipe layout and heat output
Installers typically lay pipes in either a serpentine (back-and-forth) pattern or a spiral (counter-flow) pattern. Spiral layouts tend to give more even floor surface temperatures because the flow and return pipes alternate across the room, balancing out the natural temperature drop as water travels further from the manifold. Serpentine layouts are simpler to install and work well in smaller, more regularly shaped rooms.
Rooms with higher heat loss, such as a bathroom with an exterior wall and a window, generally need tighter pipe spacing (150mm) to deliver enough heat output per m². A well-insulated, less exposed living room can often run efficiently at wider 200-300mm spacing, which also uses less pipe and slightly reduces material cost.
Installation methods
Screed system: insulation boards are laid first, pipes are clipped to the boards in the chosen pattern, then screed is poured over the top to encase them. This is the cheapest method and gives the best heat distribution because the screed's thermal mass spreads and evens out the warmth. It takes 3-4 weeks in total, since the screed needs time to cure before any floor finish goes down, and adds 50-80mm to the floor height. Most common in new builds and extensions where the floor height is being set from scratch.
Dry board system: grooved boards with pre-cut channels take the pipes without any screed at all. Floor height only increases by 18-25mm, and the floor finish can typically go down within a couple of days rather than weeks. It costs more per m² (£140-220) but is the practical choice for retrofitting UFH into an existing house where you can't afford to lose much floor height or wait a month for screed to cure.
Why wet UFH suits heat pumps particularly well
Heat pumps perform most efficiently at low flow temperatures, and wet UFH's 35-45°C operating range sits right in that sweet spot, unlike radiators, which typically need 55°C or higher to heat a room adequately and push a heat pump to work harder for the same output. This is a large part of why wet UFH is so often specified alongside a heat pump in new builds and major retrofits, rather than being paired with radiators.
Manifold and zoning control
The manifold is the hub where all the pipe loops from different rooms or zones connect back to the boiler or heat pump circuit. Each zone gets its own thermostat, usually wall-mounted, so you can run the living areas warmer during the day and keep bedrooms cooler, or heat only the rooms actually in use. Balancing valves on the manifold let an installer fine-tune the flow rate to each loop so that a room with a long pipe run gets as much heat as one closer to the manifold.
Commissioning a wet UFH system properly involves balancing these valves and bleeding air out of each loop; air locks are one of the most common causes of a cold patch in an otherwise working system.
Response time and thermal mass
Wet UFH, especially a screed system, has significant thermal mass. It takes a few hours to heat up from cold and a similar time to cool down once switched off. This makes it well suited to steady, background heating that runs for longer periods at a lower output, rather than the quick on/off bursts you'd use with a radiator or electric UFH. Many households run wet UFH on a timer that starts an hour or two before it's needed rather than switching it on the moment someone wants heat.
Cost breakdown for a 40m² ground floor
- Pipes and insulation: £1,200-1,800
- Manifold, pump and mixing valve: £800-1,500
- Screed: £600-1,400
- Labour: £1,600-2,800
- Total: £4,200-7,500
Running cost
For 40m² of living space, heated 8 hours daily:
- Gas boiler (roughly 7p per kWh): £220-330 per year
- Heat pump (roughly 28p per kWh electricity, COP around 3.5): £220-330 per year
Compare that to electric UFH heating the same space, which runs to roughly £840-1,250 per year, and the gap becomes clear why wet UFH is the standard choice for whole-house heating and electric UFH is reserved for single rooms. See our underfloor heating running cost guide for the full comparison and what drives the difference.
Maintenance and common problems
Wet UFH is largely maintenance-free once commissioned correctly, but a few issues do come up:
- Cold spots: usually an air lock in that loop; bleeding the system at the manifold, or getting an installer back to rebalance it, normally fixes this
- Screed cracking: can happen if expansion joints weren't included at doorways and large floor areas during installation; minor cracking is cosmetic, but it's worth having checked if it appears alongside uneven heating
- System pressure dropping: check and top up pressure at the manifold periodically, similar to a standard central heating system, and check for any slow leaks if it drops repeatedly
- Inhibitor: the system water should include a corrosion inhibitor, checked periodically, to protect the pipework and manifold over the system's lifetime
Retrofit vs new build
Wet UFH is easier and cheaper in new builds, since you're laying a screed floor anyway and can plan pipe routes and floor heights from the start. Retrofitting into an existing house costs more, either due to the floor height increase of a screed system or the higher per-m² cost of a low-profile dry board system, and there's more disruption involved in lifting existing floors to fit either.
Building Regulations Part L (energy efficiency) applies to new heating installations, but wet UFH itself isn't separately notifiable in the way electric UFH is under Part P; it's the associated boiler, heat pump or electrical work for the pump and controls that typically needs certifying by a qualified installer.