The specs. are;

Gas supply source - 2 tonne cylindricat gas tank
Existing supply pipe - 1/2 inch copper pipe
Existing gas stove - maximum of 4.5 kilowatts input
New open gas fire - maximum of 32 kilowatts input


The input figure (32 kilowatts) for the new open gas fire may seem
excessive, but it is correct - manufacturer's figures.
I suspect they've left out the decimal point?
Maybe it should be 3.2 Kw
unless there is a very large boiler behind it :-).

Some figures from and old catalogue which may help :-
15mm pipe dia.
pipe length- 10ft 20ft 30ft 40ft
gas flow, 108 76 62 -- cu ft/hr

& for 22mm pipe 225 160 130 110 cu ft/hr

Hope this helps
Donwill