Biomass Flue System

Grant wood pellet boilers have their own unique high temperature flue system. This 125mm (5”) vertical conventional stainless steel, twin wall insulated chimney system specifically designed for use with Grant pellet boilers. It has been fabricated to cope with continuous operating temperatures up to 200°C although the typical flue gas temperature produced by the Spira is much lower than this. The system is designed so that the stainless steel outer case is load bearing and stainless steel inner liner is free to expand independently to accommodate temperature change.

Available with a range of extension pieces and bends in a black or white finish, the system can easily be assembled to suit a wide variety of installations.


Sections are joined together by placing the female collar of one section over the corresponding male collar of the preceding section then locking by rotating the upper section clockwise. It is vital that all flue gas carrying components are installed with the external collar pointing upwards. An arrow on the label indicates the flue gas direction.

The inner of each section is enlarged at the male end so that the female end of the other section or fitting enters into it and overlaps. This allows any condensation to run back to the boiler without escaping from joints.


The flue should remain as straight as possible through its vertical run to assist flow. Should it be necessary to angle the run, an offset no greater than 45° to the vertical, with a run between the bends not exceeding 20% of the overall height of the chimney should be maintained. A vertical rise of 600mm should be allowed immediately above the appliance before any offsets. Reference for both guidelines can be found in the Building Regulations Document J and relevant British Standards on installations.


  • Twist-lock bayonet jointing system. Secured by locking bands
  • Advanced corrosion resistant design and construction
  • The 25mm high efficiency Superwool blanket maintains flue gas temperature, maximising efficiency, improving flue draught on start up and minimising condensation.
  • Low external case temperature.
  • Inner liner held by the male locking collar but free to expand and contract with temperature by up to 18mm through the female collar.
  • The inner liner has an inward bead at the female end which acts as a capillary break preventing moisture beingdrawn through the joint.

Case Studies

Grant renewables installed in hostel for homeless

  The Battery Street Hostel for Signpost Housing is a 46-bed homeless hostel situated in the Stonehouse area of Plymouth, built to provide housing for some of the city’s most vulnerable people.  Completed in July 2011 and located just off Union Street, the building replaced the Ship Hostel, which didn’tRead More

It is easy being green with a Grant biomass boiler

We revisit a factory in West Yorkshire which upgraded its existing heating system with a Grant biomass boiler just over two years ago. Installed under the non-domestic Renewable Heat Incentive (RHI), the Spira is not only keeping the factory warm but also significantly reducing the premises’ fuel costs and generatingRead More

19th century cottage now being heated by a Vortex Pro boiler

A cottage that was originally built in 1850 in a small Wiltshire village is now being kept warm by a Grant Vortex Pro 15-21kW kitchen/utility oil-fired boiler. Replacing an appliance that was over fifteen years old, the new Vortex now installed is providing reliable heating to the property, efficiently andRead More

Installer promotes advantages of renewable heating

Long established plumbing and heating installers, Great Yarmouth Heating Company Ltd, is promoting the benefits of energy saving, by kitting out their premises with an array of Grant MCS approved renewable technologies. Based on Gapton Hall Industrial Estate, GYH was founded in 1971 and has installed, serviced, and maintained GrantRead More