No way i would do that, if any moisture enters the external one it could trip internal power, i would put an isolater in between the 2 so at least separate it.
Yeah but its bragging rights that counts, my old 2009 banger failed its first mot on tyre in 2012, since then its passed every single mot upto latest mot in oct 2024 with mileage at 167k.
I bought a house in 2004, chimney breast was removed from it before i purchased it, chimney stack was still still there (supported by timber in the loft), no paperwork.
Today , no chimney stack as was removed in 2016 during dormer construction and have building regs cert for loft conversion...