Inspired by a UK underfloor heating guide. This article draws on the YouTube video "How to install underfloor heating. Full A to Z on the pros and cons of wet underfloor heating", a thorough UK walkthrough of the full process from insulation to commissioning. It's honest about what's DIY-able and where a Gas Safe engineer is needed - which is exactly the right way to approach it.
1. Check suitability and plan the layout
Wet underfloor heating works best in well-insulated rooms with good floor finishes - tile, stone, and engineered wood conduct heat well. Thick carpet with a dense underlay is less effective and can cause the floor to overheat. Check your boiler or heat pump can deliver water at the right temperature (UFH typically runs at 35–45°C, much lower than radiator systems at 70–80°C).
Draw a plan of each room, noting where the manifold will sit (usually in a corner or cupboard), and sketch out the pipe runs. Pipe spacing is typically 150–200mm for normal heating, closer for rooms with lots of external wall. Each loop should be no longer than about 120m for standard 16mm pipe - longer loops lose flow efficiency.
2. Prepare the subfloor
The floor needs to be clean, level, and structurally sound. Fill any dips or cracks in a concrete slab with a suitable levelling compound. If you're working on a suspended timber floor, you'll need a different approach - either low-profile aluminium spreader plates between joists, or a dense board system designed for timber floors. This guide focuses on the more common solid floor method.
Fit a damp-proof membrane over a solid floor if there's any risk of rising damp - a sheet of 1200-gauge polythene overlapping at joints and turned up the walls by 150mm will do. The whole point of insulating below the pipes is to stop heat going downwards, so don't skimp here.
3. Lay the insulation
UFH insulation boards typically come as 25mm or 50mm rigid polyurethane or EPS panels, often with a pre-formed channel or studded surface to locate the pipes. Fit them tightly across the whole floor area, cutting around obstacles with a sharp knife or a saw. Tape the joints between boards with foil tape.
In a ground floor room, you're looking at a total floor build-up of roughly 100mm when you add insulation, pipes, and screed - check this against your door thresholds and floor levels in adjoining rooms before you start.
4. Install the manifold
The manifold is the central distribution point - it receives water from the boiler, splits it into separate loops for each zone or room, and returns it. Fix it to the wall at a convenient height inside its housing or cupboard. It needs to be fed from the main heating circuit, which typically means a plumber or Gas Safe engineer connecting it to the boiler pipework.
Each loop port on the manifold has a flow and return. Label them as you go - it's not obvious later which port feeds which room.
5. Lay the pipe
UFH pipe is usually 16mm or 20mm multi-layer composite (PEX-AL-PEX or similar). Start at the manifold port, unroll the pipe as you work around the room following your plan, and clip it to the insulation board at roughly 500mm intervals using the clips provided or by pressing it into the board's channels.
Keep the pipe run as smooth as possible - no tight kinks. A good bending guide or spring helps on corners. Return to the manifold on the return port of the same loop. Both ends of the loop must reach the manifold: one flow, one return. Don't join pipe mid-loop; the whole loop should be a single continuous piece from port to port.
6. Fit edge expansion strips
Before screeding, fit foam expansion strip around the perimeter of every room and around any columns or fixed obstacles. When the screed heats up it expands, and without these strips it will crack against the walls. Most UFH kit suppliers include this in the kit - it's a 10mm foam strip that's easy to overlook and genuinely important.
7. Pressure test the system
Before any screed goes down, pressurise each loop to around 6 bar using a hydraulic or hand pump with a gauge, and leave it overnight. Any drop in pressure means a leak somewhere - find it and fix it now, not after the floor is covered. This is not a step you can skip. A leaking pipe under hardened screed is a very bad day.
Keep the system pressurised while the screed is poured and curing - this keeps the pipe round and under slight tension, which reduces the chance of the screed cracking as it settles.
8. Screed and commission
Pump or pour a sand-cement screed or liquid anhydrite screed to cover the pipes by at least 65mm (sand-cement) or 30mm (liquid screed). Liquid screed self-levels and is increasingly popular for UFH because it flows around the pipes with fewer voids. Let it cure fully - typically three to four weeks for sand-cement, one to two weeks for liquid screed - before laying the floor finish on top.
Commission the system slowly: start with the water temperature at around 25°C for a few days, then raise it by 5°C every couple of days until it reaches working temperature. This gentle warm-up prevents thermal shock cracking in the screed. After that, a Gas Safe engineer or qualified plumber should connect and commission the manifold mixing valve and thermostat controls.
When to call a handyman
The pipe laying, insulation, and screed work are all within reach of a capable DIYer or handyman. Connecting the manifold to the boiler and commissioning the system is notifiable plumbing work - you'll need a Gas Safe registered engineer for any gas boiler connection, or a qualified plumber for a heat pump system. Don't skip that part.
Planning underfloor heating?
The Sandwich Handyman can carry out the floor preparation, insulation board, pipe laying, and screeding stages for underfloor heating installations across Sandwich, Deal, and East Kent, working alongside your heating engineer for the boiler connection.
Contact Richard