Having installed some LV halogen lights in the bathroom, I need to
protect them against overheating or causing a fire by buring them
under 250mm of Rockwool.

I know this has been covered before here, and solutions of large
inverted plant pots (don't have any) or proprietary incandescent
shields (expensive) have been suggested.

I think I've come up with an alternative solution; that is, to use
offcuts of 4" soil pipe or ducting as 'chimneys' to surround the
fitting neatly and duct the hot air upwards (would also illuminate the
roof space quite nicely! Don't have any spare of either unfortunately
so was going to order up some Screwfix ducting (ref 15872 - five 350mm
lengths for 5.95GBP).

So - do we think this would be OK? Or might it melt if it was that
close to the fitting (50W bulb)?

Thanks
David