Which pipes are used in heating
| Pipe | Pros | Cons | Best for |
|---|---|---|---|
| Reinforced polypropylene (PP-R) | Inexpensive, reliable welded joints, does not clog | Rigid, expands noticeably with heat without reinforcement | Radiator pipework, boiler room |
| Cross-linked polyethylene (PEX) and PE-RT | Flexible, easy to lay in loops | Needs an oxygen barrier | Underfloor heating, pipework in the screed |
| Multilayer (PEX-AL-PEX) | Flexible, holds its shape, hardly expands | Fittings need maintenance | Radiator pipework, renovation |
| Steel | Strong, withstands high temperatures | Corrosion, difficult installation | Boiler rooms, industrial facilities |
| Copper | Durable, thin-walled | Expensive | Premium projects |
Polypropylene for heating
For hot water and heating, use only reinforced pipes: with an aluminium layer or glass fibre. Ordinary polypropylene pipe expands noticeably and sags when heated.
An example is PILSA composite pipes. Joints are welded with a heat-fusion tool. A correctly welded joint becomes monolithic and needs no maintenance. Welding takes experience: overheating or underheating a fitting is a common cause of leaks.
Multilayer pipes
A multilayer pipe: polymer inside and outside, aluminium in between. It bends by hand and holds its shape, and hardly expands when heated. Convenient for radiator connections and renovations where there is no room for welding. An example is VALSIR MIXAL 16×2 and 20×2, including factory-insulated versions.
Pipes for underfloor heating
For water underfloor heating, use cross-linked polyethylene (PEX) or PE-RT with an oxygen barrier (EVOH), for example SINIKON PE-RT d16 pipe. The barrier stops oxygen from entering the system and protects the boiler and pump from corrosion.
Basic rules:
- pipe diameter is usually 16 mm;
- one loop is up to 80-100 m long;
- pipe spacing is 100-200 mm, closer near external walls;
- inside the screed — only continuous pipe, no joints;
- all loops are connected to a manifold with flow adjustment.
Can underfloor heating and radiators run from one boiler? Yes, but the circuits must be separated by temperature using a mixing unit.
What diameter you need
For a private house, the guideline is:
| Section | Typical diameter |
|---|---|
| Connection to a single radiator | 16-20 mm |
| Branch to several radiators | 20-25 mm |
| Main line from the boiler | 25-32 mm |
| Underfloor heating loop | 16 mm |
The exact diameter depends on the flow rate and the length of the run. A pipe that is too thin causes noise and underheating of distant rooms.
How to conceal heating pipes
- In the floor screed. The neatest method. The pipes are laid in thermal insulation so they can expand.
- In a wall chase. Only continuous pipes or permanent joints: press fittings, welding.
- In a boxing or behind plasterboard. Detachable joints are kept accessible through an access hatch.
- Behind the skirting board. For short sections along the wall.
Threaded and compression fittings must never be buried in walls or screed. Before the screed or boxing is closed, the system must be pressure-tested.
Important: pipes, fittings and the manifold are best taken from one system by one manufacturer. This makes it easier to ensure tightness and get a warranty.
Send ThermoHouse your house plan — we will advise which pipes and fittings suit your radiators and underfloor heating and put together a kit for your project: PILSA, VALSIR MIXAL, SINIKON. Contact us →
