Boat stove improvements

[Gipsymac]

I have just fitted a new multi-fuel stove on our narrowboat, replacing a Morso Squirrel, which worked very well on both wood and coal (Supertherm) until getting to the stage where it was easier to replace than repair.

The new stove is a Parkray 4 multifuel. Nothing has changed about the installation; the flue length and size is the same as on the Morso. However, the stove burns wood perfectly well, but only burns coal - also Supertherm as before - very slowly. The problem seems to be related to the draw of the stove - there is plenty of bottom air. What experience does anyone have of increasing the draw?

 

I have seen increasing the length of the flue, which will be tried at the weekend with a longer chimney and also seen rotary chimney cowls. Do they work?