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Post by bryani on Oct 3, 2018 7:52:13 GMT -8
I'm building a 6" (150 mm) system with a two bells (a barrel and a bench). The barrel size is 71” (circumference) x 36” (height) with a 23” diameter barrel end (180.34 cm x 91.44 cm with 58.42cm diameter barrel end) and the bench will be 132" x 16" x 16" (335.28cm x40.64cm x40.64cm). I've calculated the total barrel ISA = 11.89 sq ft = 1.11 sq meters and total bench isa = 6592 sq in = 45.78 sq ft = 4.25 sq meters. If my calculations are correct the total ISA of barrel and bench = 1.11+ 4.25 = 5.36 sq meters. I have read that the recommended bell size in 150 mm system is 5.3 m2 so my system, if calculations are correct is a bit over the recommended size.
My thought is that it would be better to undersize the total bell ISA a bit to make sure that the flue temperatures are hot enough for a good draw and I'm thinking that I will reduce the bench length to from 132" to 120" (304.8 cm)
Any thoughts and recommendations are most appreciated.
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Post by peterberg on Oct 3, 2018 10:55:05 GMT -8
Be careful with a double bell system. It won't work the same way a single one. Mainly because two bells are more efficient than one, so both together should be 15% less in total ISA. It's different again when the bench is completely open to the main bell, in that case the combination acts like a single bell. I'd think in your case, using a barrel, it's safer to under size the thing so you are assured of sufficient chimney temperature.
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