Which flue factory in Changsha has the patent right to produce "combined fire-resistant flue"?

Changsha Yuhua District Fire-resistant Flue Building Materials Engineering Technology Center has obtained the exclusive patent right of the combined variable pressure fire-resistant exhaust flue in Hunan Provincial Architectural Standard Design Atlas "Residential Kitchen and Bathroom Combined Fire-resistant Exhaust Duct" (the atlas number is "Xiang 20 12J902").