My Second Version of the One Drum Boiler

On the occasion of my marriage, I moved to a newly constructed homestead and it was time to design and construct my Mark II donkey boiler:

• This was side stoked, as in my Mark I, but retained the basic layout of the classic Rhodesian boiler. The firebox remained the same size - 12" (300mm) wide and 12" (300mm) tall, but was offset toward the end away from the flue. This version was equipped with a fire grate (closer spacing than the Mark I) and an ash box.
• The lid of the boiler was made from a heavy gauge steel sheet, through which the drum could be easily exchanged - the plumbing exited through the masonry wall opposite the chimney.
• The flue exited from the end of the drum into a tall masonry chimney - the placement of the flue, however, was lower than usual. The placement opposite the lower rim of the drum allowed a greater proportion of the drum to remain above the flue exit, thus better trapping heat overnight.
• The tall chimney was necessary to lift the woodsmoke above the double story cottage. The internal dimensions ended up 9" square (225mm square.)
• Flue gases curled up and over the top of the drum from behind, before dropping down the end of the drum and exiting via the flue.
• The annulus around and to the end of the drum remained 3" (75mm), and the space to the front of the drum was restricted by popping a few loose bricks into the gas (this prevented the fire front from migrating toward the front of the firebox.)
• Unfortunately, in this case, I constructed the firebox lining from concrete blocks in order to reduce wear and tear on the walls of the firebox. Consequently, the fire burnt rather cool, and smoke often poured from the top of the chimney.

This boiler functioned very well - a bath could be drawn from a single load of wood within 30 minutes, and with no further attention, the boiler would retain sufficient heat for morning ablutions. The firebox remained relatively undamaged through 15 years of use, however, the concrete block lining is a poor choice from other perspectives. The tall chimney always provided plenty of draft and the low placement of the flue prevented excessive cooling overnight.

I would recommend this design, provided that the construction of the firebox lining is exchanged for insulating (soft burnt) brick and a suitable sheet of steel is available for the lid. This design could be topped off with a flat concrete roof or with a masonry arch - in this case arrangements must be made to exchange the drum from the end (brick in with adobe.)