Chasing Heating Pipework

A good result starts with planning. The installer first finds out how the floor is built up. In a typical flat there is impact sound insulation on top of the structural floor slab, then a screed, and on top the tiles or another floor finish. The chase belongs in the screed, not in the structural slab.

1. Mark the route directly on the floor, following the design or an agreed sketch. Keep it as short as possible, with as few bends as possible.
2. Check the route with a detector for electrical cables, water pipes or existing underfloor heating.
3. Remove the floor finish in a strip above the route, for example by lifting the tiles.
4. Cut two parallel lines with a wall chaser or an angle grinder with a diamond blade and break out the material between them.
5. Clean the chase of dust and debris.
6. Lay the pipe in its insulation sleeve and fix it so it cannot move during filling.
7. Carry out a pressure test, then photograph and measure the route.
8. Fill the chase with repair mortar and, once it has dried, reinstate the floor finish.

Why a pressure test before filling? Because once the chase is filled, a leak is hard to find and fixing it means breaking up the floor again. Photos with measured distances from the walls are worth having years later, when someone drills into the floor or replaces the tiles.

Most floor chases take plastic pipe, typically multilayer pipe (plastic with an aluminium core), PEX or PB. It is run in one length, ideally with no joint at all between the manifold or riser and the radiator. Copper pipe is also used, but in a floor it needs insulation or a protective sleeve so it is not in direct contact with the mortar.

Pipe insulation is not only about heat loss. The pipe expands as it warms up, and the soft sleeve gives it room to move. Without it, the mortar above the chase can crack and the pipe may creak or tick.

Chasing is not the only option. If a new floor is going in, the pipe can often be laid in the insulation layer under the new screed, with no chasing at all. In other cases it can run in the wall, behind a plasterboard lining or inside a special skirting duct. It is worth comparing these options before you decide.

How demanding the job is, and therefore the price shown on the page, depends mainly on these things:

• Floor material: hard reinforced concrete cuts slowly and needs powerful tools, while older or softer screed is quicker
• Screed thickness: if it is thin, the chase barely fits and another route may be needed
• Floor finish: lifting and relaying tiles takes more work than exposing bare screed in an unfinished flat
• Length and shape of the route: every bend and every crossing under a threshold or wall slows the work
• Access and furnishings: a furnished, lived-in room means covering things, moving furniture and more thorough cleaning
• Rubble removal: in a building without a lift, it has to be carried down the stairs

In blocks of flats built from precast concrete panels or with concrete floor slabs, there is often only a thin screed directly over the reinforced concrete slab. The chase must not be cut into that slab. Damaging the reinforcement weakens the load-bearing structure, which belongs to all the owners in the building. If the screed is too thin for a chase, choose another route or ask a structural engineer for advice.

Before work starts, contact the building management or owners' association. Central heating in a block of flats is a shared system, so draining the water, working on a riser or connecting new pipework always has to be agreed with them. Noisy work is usually covered by the house rules, and it is courteous to let your neighbours know in advance.

Whether your alteration needs any approval depends on the scope of the work and on whether load-bearing parts are affected. Local building regulations differ, so do not guess: check with your local building authority. Connecting to the heating system and carrying out the pressure test should be done by a heating engineer who takes responsibility for the work.

• A chase that is too shallow, leaving only a thin layer of mortar over the pipe, so the tiles crack later
• Pipe without insulation, which moves with temperature changes and breaks up the mortar
• A joint buried in the floor when the fitting manufacturer does not allow that use
• Filling the chase without a pressure test
• Cutting through an electrical cable or water pipe because the route was not checked first
• Crossing a movement joint without a protective sleeve
• Cutting into the structural slab in a block of flats
• No photos or measurements of the route, so after a few years nobody knows where the pipe runs

Cutting concrete produces fine dust containing silica, which damages the lungs. Professionals therefore cut with extraction into a vacuum with a fine filter, or cut wet, and wear a respirator. Furniture and the doors to other rooms should be covered with plastic sheeting.

At handover, focus mainly on what will no longer be visible once the chase is filled. That is why it helps to be there before the filling is done.

• The pipe is fully insulated along the whole chase and firmly fixed
• There is no unnecessary joint in the floor, and any joint is a fitting approved for burying
• The pressure test was carried out and the pressure did not drop during the test
• You have photos of the route with measured distances from the walls
• The chase is filled flush and the mortar shows no cracks
• No cables or other services nearby have been damaged
• After filling and bleeding, the radiator heats evenly and the connections are dry
• The room is clean and the rubble has been removed