The cup or recess in your CoffeeBOS siphon brew board is designed to accept an adjustable butane burner. These burners can be turned on “high” for bulk heating. They can be turned on “low” when the brew water has risen up into the funnel. With a little practice, you will be able to intentionally, accurately and repeatedly manage your brewing temperature within a very tight range.
On the one hand, the Cona brew boards have a 3.5″ diameter cup for the butane burner, which is roughly the diameter of the hole in the base of the brewer. On the other hand, the Japanese-style brew board, like those for the Hario TCA models, have a smaller diameter hole (3.375″) and require a smaller diameter burner to fit within the forks of the brewer. The three butane burners that I own range between 3.125″ and 3.4″ in diameter, and all nest very neatly inside the base of the Cona brewer. However, while I can use all three of these burners with a Cona brew board, only the two smaller burners work with my Hario brew board. These burners are all roughly 3″ tall.
If you are shopping for a new butane burner, I can personally recommend the Rekrow RK42013 for Japanese-style brewers and the B302 professional grade micro burner for Cona vacuum coffee makers. Both these units put out plenty of heat for larger volume brewers, like the Cona Model C or D or the Hario TCA-5, and are adjustable enough on the lower end to accommodate smaller volume brewers, like the Cona Model A or B or the Hario TCA-3 or TCA-2.
The Rekrow RK4203 is undoubtedly the most common butane burner used for siphon brewing. Since it is often sold with Yama brewers, it is occasionally identified (incorrectly) as a Yama butane burner. Once you pick up this butane burner, you will have no doubt about the quality of its construction. It feels substantial, like it is built to last. The adjustment dial is responsive, and may take some getting used to. When I last looked, Prima Coffee had the best price on this burner. While the Rekrow burner is ideal for use with Japanese-style siphon brewers, it has two shortcomings when used with a Cona brewer. First, the depth of the cup plus the height of the Cona base may not allow provide adequate clearance for the lever-actuated ignitor. This can be solved by lifting or shimming up the burner, but is an inconvenience. Second, the Rekrow burner has a dome-shaped fuel reservoir, the shape of which is not ideal for pinning the Cona brewer to the brew board.
The B302 professional grade micro burner (pictured above) is actually the best fit with a Cona brew board setup, in part due to the push-button ignitor. While there are no manufacturer markings on this burner, Google seems to attribute this burner to the vendor YTC Summit 1234. Based on its shape and diameter, this butane burner likely holds a bit more fuel than the Rekrow. It also has a broad flame head. This is a powerful butane burner in terms of BTUs, which is a nice feature if you have a relatively high volume brewer. While perhaps not equal to the Rekrow in quality of construction, it is comparable to it in terms of performance. Best of all, the fuel reservoir of the B302 burner has steep “shoulders,” and this form factor does a great job of pinning the Cona armature in place atop the brew board. The only real downside to the B302 burner is that its diameter is too large to fit Japanese-style siphon brew boards.
In summary: the B302 burner WILL NOT fit Japanese-style brew boards, but is ideal for Cona brew boards. While the Rekrow burner will fit Cona brew boards, it is best suited for use with Japanese-style siphons, like the Hario TCA models. Therefore, I use the B302 burner exclusively with my Cona brew board and a Rekrow burner exclusively with my Hario brew board.