all depends on what your firing it with – gas=no, coal=definately. Ive never seen any coal fired boiler without one…and ive made and seen a few.

If you need the fan to get a decent flame and without it you suspect incomplete combustion, I'd suspect you may have insufficient air supply to the burner, or insufficient chimney area.

Gordon

Incomplete combustion is something we see with small burners, just put a CO meter near one, be they ceramic, mesh or brass. All three have different burn characteristics. I use solid brass in my commercially availible boilers as they produce the most heat, they are quiet fierce compared to ceramic. I only use ceramic in the twin flue 5" boiler as their sublime nature makes for much easier firing of both flues at the same time. A well designed burner needs no chimney as all of the combustion products are supplied from outside the burner. You will see slits in the sides of PSB burners but these have absolutely nothing to do with the combustion process. Invariably if you have your gas mix too rich a blue flame will be seen where it exits the chimney – check with lights off as it can be difficult to see. Whilst a more stable flame is seen when a chimney is present I can produce effective boilers without a chimney. An option is to have the steam return plumbed into the chimney but this is for authenticity rather than efficiency and i have not noticed any improvment in output.. My advice is…run exit steam through chimney but there should be no reason to add a stand alone blower, especially in a boiler so small.