Installation of a Schiedel Chimney System with Ceramic Liner

A Schiedel-type chimney has three layers that fit precisely into each other:

• An outer shell of chimney blocks, usually lightweight concrete, which carries the whole chimney and protects the surroundings from heat
• Insulation between the shell and the liner, which keeps the flue gases warm so that less condensation forms inside the chimney
• A ceramic liner, which resists high temperatures, moisture and the acids in flue gases

The system also includes special parts: a base unit with a tray that drains condensate, a section with a cleaning opening and door, a connection piece for the flue pipe from the boiler or stove, and the top above the roof, meaning the chimney head with its cover plate. A ventilation shaft often runs alongside the flue as well.

1. Check the base. A chimney is heavy, so it must stand on a solid foundation or on a floor slab designed for that load. The base must be flat and level.
2. Set the base unit. The first block goes into mortar and is levelled exactly. Any error grows with height and the chimney starts to lean.
3. Fit the condensate tray and cleaning section. The tray with its drain goes at the very bottom, with the cleaning section above it. These parts are installed in sequence with the rest, not added later.
4. Lay the shell and insert the liners. The blocks are laid in the mortar the manufacturer recommends. The ceramic liner sections are joined with a special acid-resistant sealant. Excess sealant is wiped off straight away so no ridges form inside the flue. The insulation goes in as the system specifies, keeping the liner centred.
5. Fit the connection piece. It is set at the height that matches the boiler, stove or fireplace. Measure this height in advance, because drilling into a finished chimney later is an unnecessary risk.
6. Pass through floors and the roof. Leave the specified gap between the chimney and timber joists, rafters and other combustible materials. Nothing combustible goes into this gap.
7. Finish the chimney head. Above the roof, the chimney is topped with a cover plate. The outside is rendered with a weather-resistant render, clad, or fitted with a ready-made head casing. Where the chimney passes through the roof, it is flashed and sealed.

Why must the liner never be built rigidly into the shell? Ceramic expands when it heats up. If it has nowhere to go, the shell cracks. That is why the system relies on a loosely seated liner and expansion joints, especially at the cover plate.

The system depends on what you plan to connect:

• Open fires, wood-burning stoves and boilers for wood, pellets or coal need a chimney rated for high flue gas temperatures and resistant to soot fires
• Modern gas and condensing boilers produce cool, moist flue gases, often under positive pressure, so they need a liner suitable for wet operation or another solution specified by the boiler manufacturer
• Two appliances, such as a stove and a boiler, usually need two separate flues; connecting them to one flue is only possible if a calculation allows it

The flue diameter and chimney height should be set by a designer or chimney specialist according to the appliance output. A flue that is too wide draws poorly, just like one that is too narrow.

The effort involved, and therefore the cost, depends mainly on:

• The height of the chimney and the number of storeys it passes through
• The number of flues and whether there is a ventilation shaft
• Whether it is a new build planned with the chimney from the start, or an existing house where floors and the roof have to be opened up
• The condition of the base, if a new foundation or a strengthened floor is needed
• Access to the roof and the need for scaffolding to build the head
• How the head is finished: render, cladding or a prefabricated casing
• Carrying heavy blocks into a loft or up a narrow staircase

In practice the laying itself often takes less time than the roof penetration, where rafters have to be adjusted and the roof covering rebuilt around the chimney.

Whether a new chimney on your house needs a permit, a notification or nothing at all depends on local building regulations. Check with your local building authority before work starts rather than assuming it is a minor job. In a block of flats you need consent from the building management or owners' association, because the chimney affects shared parts of the building.

Before the first fire, the finished chimney should be inspected by a chimney sweep or another qualified inspector, as local rules require. Without this sign-off you may not be allowed to use the chimney, and after a fire it can also cause problems with your insurer. Only a qualified, registered gas engineer may connect a gas boiler, and only a qualified electrician may do any electrical connection. If you smell gas, leave the room and call 112 or your local emergency number.

• The base unit is not level and the chimney gradually leans
• Liner sections joined with ordinary mortar instead of acid-resistant sealant
• Sealant squeezed into the flue, where it catches soot
• No expansion allowance for the liner, so it presses on the shell and the cover plate cracks
• Timber joists or roof insulation right against the chimney without the required gap
• A chimney that ends too low above the roof, so it draws poorly and smoke blows back in windy weather
• A badly sealed roof penetration that lets water into the loft
• A missing or unconnected condensate drain

• The chimney is plumb, checked with a spirit level or plumb line at several points
• The cleaning opening is accessible and the door seals well
• The condensate tray is in place and the drain is connected
• The connection piece sits at the height that matches the appliance
• No combustible materials in the floors or roof structure are closer to the chimney than the manufacturer allows
• The chimney head is high enough above the roof and the cover plate is intact, with no cracks
• The roof penetration is flashed and does not leak
• The render or cladding on the head is continuous and free of cracks
• You have the documents for the chimney system and the inspection report