Technical Booklet L Combustion Appliances and Fuel Storage Systems·Page 73·5.13
Chimney provisions for flue gas temperatures greater than 250°C
Oil-fired appliances with flue gas temperatures exceeding 250°C must use masonry or flue block chimneys in accordance with Sections 2 and 3, or a factory-made metal chimney compliant with Section 2.
The chimney, flue and flue pipe for an oil burning appliance, with a flue gas temperature greater than 250ºC, should be – (a) in accordance with the provisions given in Sections 2 and 3 for a masonry or flue block chimney; or (b) a factory-made metal chimney in accordance with Section 2.
Source — /Users/richardhill/Documents/planning-arch-project/data/documents/regional/Technical Booklet L - Combustion Appliances and Fuel Storage Systems.pdf