How close can triple walled polycarbonate be placed to a combi boiler vent?

I'm roofing a small back porch in clear polycarbonate (it'll be a dark dungeon otherwise) but next door's combi vent is at the same height as the roof. It'll be cheaper for me to fiddle some 3d origami than to pay to have his vent moved. I'm planning on placing a metal plate under the vent (about 50mm below it) attached to the wall. It'll be about 300mm by 150mm to match the size of the vent but a bit bigger

What I'd like to know is can the poly touch the plate at the specified dimensions or should the plate be bigger or should there be some form of thermal gap (air or wood or ?) Space is too tight for the poly to be placed under the plate.

I will be placing a off cut of poly under the vent for a few days to see what happens, but I don't want to over engineer a solution if I can get away with less.

All the boiler manufacturers give these following tolerances and distances for flue proximity to objects:

http://www.worcester-bosch.co.uk/index.php?fuseaction=product.detail&con_id=1221...

So are dimensions i and k the ones you need?

HJ, i know this might sound daft, but when the boiler is running, have you tried to "gingerly" put the BACK of your hand to the side of the flue!! is it very hot!??, i ask this as the majority of flues these days are two compartmented, the outer area of the flue is the AIR INTAKE to the boiler, and the centre section is the exhaust discharge!! for reasons of trying to keep the heat transfer to the outer most edges of the flue "cooler" than just a discharge only flue!!  on my workshops washroom , i have a std boiler "twin" flue at about 12" away from just std clear corrigated poly sheet, and has been for about 8 years, with no ill effect!!
just a thought!!!

[quote author=WOLF  link=1133556172/0#4 date=1133688014]HJ, i know this might sound daft, but when the boiler is running, have you tried to "gingerly" put the BACK of your hand to the side of the flue!! is it very hot ........... on my workshops washroom , i have a std boiler "twin" flue at about 12" away from just std clear corrigated poly sheet, and has been for about 8 years, with no ill effect!! [/quote]

It's not that hot. I can put my hand right over the exhaust and not get burnt, but I don't know how the poly will cope for long periods. I can always move my hand but not the poly. Though if it last 5 years then needs replacing I could live with that since it's only about £30 for a sheet of poly.

12" is something for to work from. The fact that it's lasted so long means that is a good minimum for me to work from.

We've hadn't about glass, thinking it'll be too awckward to install and heavy to boot. Also it would have to be obscure since next door's landing window would look into the porch. With poly I just need 3 3000x900 sheets to cover the whole porch and only need a simple purlin in the centre to hold up the poly.