Thank you. A lot of this all is on your expence. Without your help things wuldnt turn out so good for sure.
Correct. I guess some air gets drawn in by the venturi effect but not enough. Still it burned well.
No hach. For now. We decided to try eliminating the chimney all together and just extend the existing pipe ~ a meter, then with a strong fan and a good ejector provide the nesseeery draft and regulation. The reasons behind are the boiler will stand on its own near to the pool, in the open, and having a 7m pipe sticking out in the air, ancered with cables, just isnt practical. Second reason is shuld one of the water pumps fail, the boiler wuld overheat in minutes and since this must be a hands off system when in operation, such a failiure wuld be catastrophic. When using no natural draft, a safety overheating sweech can be hooked on the fan killing it if overheating is detected. This will quickly suffocate the burn.
Primary air enters on top 2 corners of the top door.
Well this was the most elegant solution for chimney position. A brush on a rigid steel cable shuld do the job of sweeping the heatex tubes.