posted 8 years ago
Rob, i have done it, from 139mm, to 111mm. Worked vaguely ok.
Done it on 150 to 111. Worse. Still worked. This is with J tubes.
I have done it with a batch, having all the piping the same as the system tube, except the transition going through the wall, about 70cm long, which was still 111mm. Worked surprisingly well.
Then i moved place. And going through a proper chimney makes a world of difference. Now i go from 220mm batch system, to 20cm square chimney.
So try hard to find the proper piping for your system.