This rare kanji has no clear standalone meaning. Treat its meaning as uncertain.
煹 combines 火 (fire) with 冓, which likely contributes the sound. The exact historical development is uncertain.
The left side is fire 火, and the right side is 冓. Without a clear meaning, picture a mysterious fire burning inside a structure shaped like 冓.
For コウ, imagine a coal fire burning inside the 冓 structure: coal -> コウ, and the fire keeps it glowing.