Might be worth talking to Merryhill down your way, they do all our Asbestos removal/disposal on our Southampton contract, extremely good value against some we have used.
Sorry OP, bit off topic.
It is, probably an unfair comparison if i'm honest, as we spend upwards of a million a year on skips, but more trying to identify what they make out of the 'A' word to your everyday fellas.
Phone your local skip company and ask how much dedicated skip for Chrysotile Asbestos is.
Failing that, multi drop at tip once it's been wrapped and taped.
I would also view a barn as commercial.
If there is no coil in it, how is the water getting heated ?
I habe a Rayburn doing mine, small tank to feed the heating circuit, through the coil in the tank.
Looks plastic to me...Felt will have metal flange.
http://www.ubbink.co.uk/products/Roofing/Roof-vents-terminals/Flat-roof-(1)/OFT-Vent-and-Terminals-(1).aspx