I don't know why such a simple issue has been bothering me for weeks. Im doing multiple jobs around the home and hopefully nearly finished.
A few months back I replaced flex ducting that an electrician had put in for ducting on a cooker hood.
I replaced the flex ducting with semi rigid ducting from b&q. Much better feel to it now and obviously much safer.
At the time I just patched up the large'ish gap around the ducting where the ducting goes through the ceiling, into the loft and up to a roof vent. At the time I think I just stuffed some plastic bags around it to keep any cold out and until I could look into exactly what sealant was needed.
I read that certain sealants react with certain materials and also that for heat sources I should not use ordinary silicone.
Ive got a large tub full of caulks and sealants which I have collected since then for various jobs. Ive got soudal genius gap filling expanding foam, ive got silicone and solvent free silicone, ive got Intumescent Sealant, and decorators caulk.
I just wanted to check with the experts first before I used anything.
Thanks for your time and feedback. Much appreciated.
Teddy