Isokern

Isokern is a leading brand specialising in high-quality chimney solutions made from natural volcanic pumice sourced from Iceland. These pumice-based liners and systems are designed for masonry chimneys, offering superior insulation and performance for non-condensing appliances such as wood-burning stoves, open fires, and multi-fuel systems. The pumice material acts as a natural insulator, setting Isokern apart from traditional clay or stainless steel chimneys by maintaining optimal flue gas temperatures, reducing condensation, and improving overall efficiency. They are ideal for new builds, extensions, and relining existing chimneys in the UK, providing a cost-effective, lightweight alternative that complies with UK Building Regulations (e.g., Approved Document J).

The core product line includes straight liners, bends, firechests (such as the Magnum Firechest), gathers (including Manor Gathers and Concrete Gathers), adaptors, and full systems like the DM54 (a zero-clearance modular chimney) and standard pumice liner packs. Additional products like the Garden Fireplace enhance outdoor applications. These are used in residential settings to create safe, efficient chimneys that enhance heating appliance performance while minimising heat loss and structural risks.

Material and Construction
Crafted from lightweight volcanic pumice, which provides excellent thermal insulation, resistance to temperature fluctuations, and minimal expansion/contraction to prevent cracking. Liners are available in 600mm or 1000mm lengths for fewer joints and faster assembly.

Bends and Offsets
Available in 15°, 30°, and 45° angles; up to two offsets (four bends) per chimney, with a maximum 45° from vertical. Steel collars and lip glue secure cut joints.

Insulation
Isokern liners require a minimum 15mm layer of LECA (lightweight expanded clay aggregate) mix (20:1 LECA to OPC cement) between liners and surrounding masonry.

Joint Sealing and Adaptors
Pumice to Pumice Joints sealed with specialised lip glue (about 2mm thick); stainless steel adaptors connect to stove flue pipes with high temperature glass fibre rope seals.

Safety and Construction Notes
Non-combustible clearances (200mm from flue inner surface or 40mm from masonry exterior); lead DPCs, flashings, weep holes, and rain caps to manage moisture.

Magnum Firechest
Modular firechest for open fires, with openings from 500mm to 1250mm wide, cast from insulating pumice. Includes optional damper to reduce heat loss, load-bearing up to 2600kg, and efficiencies of 41-45% for wood burning.

Manor Gather
Pumice fireplace gather hood with internal widths of 933mm or 1191mm (e.g., 1150 Centre Hole model: inside flue 350mm, external 1350mm wide x 930mm high), resistant to temperature changes and highly insulating.

Garden Fireplaces
Outdoor models in 500 (slimline with single wood store) and 950 (larger with double wood store) variants and 1200, made from durable volcanic stone/concrete mix, lined with fireclay bricks, including mortar, plaster, and grate.

Concrete Gathers
Structural gathers like C16 (for 200-225mm flues), C17 (250mm, e.g., 1000x550x300mm), C18 (300mm), suitable for open fire type installations.

Certification
CE marked to EN1857 (T450/T600 N2 D 3 G), suitable for all fuels except condensing appliances (e.g., no pellet or biomass boilers).

Maintenance
Designed for easy sweeping with polypropylene brushes; if properly installed and maintained, the system lasts the dwelling's lifetime.

Efficiency and Performance
Pumice insulation helps flue gases reach optimal temperatures quickly, allowing appliances to perform at peak shortly after lighting. It keeps chimneys warmer longer, reducing soot buildup and condensation risks compared to non-insulated systems.

Cost-Effective
Reduces reliance on gas/electric heating; lightweight design enables one-person installation (most cases), reducing man hours and construction costs. Ideal during power outages as a reliable alternative heat source.

Durability
Strong resistance to thermal stress; pumice's natural properties outperform other materials by keeping flue gases above the dew point for longer.

Versatility
Suitable for indoor/outdoor, internal/external chimneys; works with stoves, open fires, and inglenooks. Easy to cut and handle for custom fits. Magnum Firechest offers quick assembly (<1 hour); Garden Fireplace adds outdoor coziness with integrated wood stores; Manor and Concrete Gathers provide robust transitions for open fires.

Environmental and Safety
Promotes clean burning with dry seasoned wood; complies with regulations for safe, long-term use.

Sizes and Components
Diameters up to 600mm internal diameter, matching standard stove outlets (e.g., 150mm-300mm for residential use). Lengths 600mm or 1000mm on pumice liners.

Applications

New Builds and Relining
Perfect for constructing or upgrading masonry chimneys surrounded by at least 100mm brick/block/stone.

Stove Installations
Recess or free-standing setups; minimum 600mm flue pipe before liner connection; soot doors for maintenance.

Open Fires
Use Magnum Firechest and gathers (Manor or Concrete) for structural support.  Render, or masonry chimney stacks possible

Outdoor Use
Garden Fireplace for patios, free-standing or against walls, with integrated wood stores and now full outdoor kitchens.