+3 photos Darco GCK Chimney Draft Generator 150mm Diameter with Tubula Sunday, July 23, 10:32 PM - DIY Darco GCK Chimney Draft Generator 150mm Diameter with Tubular Base. The draft generator is a chimney cowl mounted on top of a ventilation, combustion or smoke chimney (only wood-fired boilers ... KT15 Addlestone £109.99