Ben Deacon, via e-mail:
I’m installing a 30kW log burner and have been told to use 904/904 flue parts. However, when I contact suppliers, all of them are advising me to use 316 grade. Is this the preferred option or is it solely down to mark up profit? And, are there any obvious ‘health and safety’ matters that I could be breaking by installing 316 grade?
Robert Burke, technical and standards manager at HETAS:
It is now a requirement across Europe to use a chimney that has been tested by a notified laboratory to the relevant EN standard. For metal chimneys, the relevant standards are: “BSEN 1856 -1 Chimneys, Requirements for Metal Chimneys Part 1: System chimneys”, which covers twin wall ridged metal insulated chimneys and “BSEN 1856-2 Chimneys, Requirements for Metal Chimneys Part 2: Metal liners and connecting flue pipes”, which covers rigid and flexible flue liners and connecting flue pipes.
The BSEN’s are not material specific and base the requirements on performance testing, which includes: mechanical resistance, resistance to fire, gas tightness, safety in use and durability.
The UK National Annex to the standard has given a table of recommended materials for use as flue linings used with appliances burning solid fuel and having a rated output up to 45kW. This table includes 316 grade stainless steel.
So from this, we are assured that chimneys manufactured from 316 grade stainless steel and tested by a notified laboratory to BSEN 1856 are fit for purpose. The chimney used with a wood burning appliance should at least be to the designation T400 N2 D3 G, which means it is suitable for use as a natural draught chimney, with a nominal flue temperature of 400º, for non-condensing use, with a corrosion rating of three (highest rating) and be soot fire resistant.
I must however stress that with wood burning there is an onus on you to burn the correct quality of firewood. It is extremely important to only burn clean dry wood, as wet wood will suppress the fire preventing complete combustion. This leads to substantially increased exhaust emissions and a much higher corrosion load on the appliance and chimney, increasing the likelihood of the chimney becoming tarred up and heightening the possibility of chimney fires.
High moisture content will also substantially reduce the heat output from the wood, costing you more in the long run. HETAS run a Solid Biomass Assurance Scheme (SBAS) for firewood producers that supply firewood of a suitable quality. Always look for the SBAS logo from your firewood supplier.