ROUND CHIMNEY (Diameter)		SQUARE CHIMNEY		SIZE OF OPENING SERVED
inches	mm	inches	cm	sq inches	sq cm
5	127	4.4	11.2	157	1,013
6	152	5.3	13.5	226	1,458
7	178	6.2	15.8	308	1,987
8	203	7.1	18.0	402	2,594
9	229	8.0	20.3	509	3,284
10	254	8.9	22.6	628	4,052
11	279	9.7	24.6	760	4,903
12	305	10.6	26.9	904	5,832
13	330	11.5	29.2	1,061	6,845
14	356	12.4	31.5	1,231	7,942
15	381	13.3	33.8	1,413	9,116
16	406	14.2	36.1	1,608	10,374
17	432	15.1	38.4	1,815	11,710
18	457	15.9	40.4	2,035	13,129