Midtherm Midflex Flexible Flue Liner

Midtherm Midflex is a class 1 flexible flue liner produced in both 316L and 904L grade Stainless Steel. It is manufactured under Midtherms ISO 9001 accredited quality management system, with CE Certification and is a HETAS registered manufacturer.

To be used for multifuel, wood burning, biomass, pellet, gas and oil applications.

Product Specifications:

  • 316L has a good resistance to pitting and crevice corrosion and 20 year warranty.
  • 904L has high levels of Chrome, Nickel, Molybdenum and copper which provides excellent corrosion resistance and very good resistance to stress corrosion cracking. 904L has a 35 year warranty.



The inner wall has a smooth bore construction which means it has very low resistance to the flue gas flow with a convoluted out profile with a crimped and locked seam. This ensures stability and integrity.


Operating Temperatures:

600° Celsius normal operating for solid fuel applications. Gas and Oil are lower at 250° Celsius. The Thermal shock resistance temperature is 1000° Celsius for short duration in emergencies.