PART 9 — HOUSING AND SMALL BUILDINGSUpdated for the 2024 Ontario Building Code
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9.21.2.5.Fireplace Chimneys
(1) The size of a chimney flue serving a masonry fireplace shall conform to Table 9.21.2.5.-A or Table 9.21.2.5.-B.
Table 9.21.2.5.-A
Diameter of Round Flues for Fireplace Chimneys
Forming Part of Sentence 9.21.2.5.(1)
Chimney Height, m
3.0 to 4.5 > 4.5 to 5.9 > 5.9 to 8.9 > 8.9 to 12
Fireplace Opening, m²
Flue Diameter, mm
Min. Max. Min. Max. Min. Max. Min. Max.
Up to 0.150 110 170 100 160 90 150 90 150
0.151 to 0.250 150 210 130 190 130 190 120 180
0.251 to 0.350 180 240 160 220 150 210 140 200
0.351 to 0.500 220 280 200 260 190 250 170 230
0.501 to 0.650 260 320 230 290 220 280 200 260
0.651 to 0.800 290 350 260 320 240 300 220 280
0.801 to 1.00 330 390 290 350 270 330 250 310
1.01 to 1.20 360 420 320 380 300 360 270 330
1.21 to 1.40 390 450 350 410 330 390 300 360
1.41 to 1.60 420 480 380 440 350 410 320 380
1.61 to 1.80 — — 400 460 370 430 340 400
1.81 to 2.00 — — — — 400 460 360 420
2.01 to 2.20 — — — — — — 380 440
Table 9.21.2.5.-B
Rectangular Flue Sizes for Fireplace Chimneys
Forming Part of Sentence 9.21.2.5.(1)
Chimney Height, m
3.0 to 4.5 > 4.5 to 5.9 > 5.9 to 8.9 > 8.9 to 12
Fireplace Opening, m²
Flue Size, mm
Min. Max. Min. Max. Min. Max. Min. Max.
Up to 0.150 200 × 200 200 × 200 100 × 200 100 × 200 100 × 200 100 × 200 100 × 200 100 × 200
0.151 to 0.250 200 × 200 200 × 200 200 × 200 200 × 200 200 × 200 200 × 200 200 × 200 200 × 200
0.251 to 0.350 200 × 300 200 × 300 200 × 200 200 × 300 200 × 200 200 × 200 200 × 200 200 × 200
0.351 to 0.500 300 × 300 300 × 300 200 × 300 200 × 300 200 × 300 200 × 300 200 × 200 200 × 300
0.501 to 0.650 300 × 300 300 × 400 300 × 300 300 × 300 300 × 300 300 × 300 200 × 300 200 × 300
0.651 to 0.800 300 × 400 300 × 400 300 × 300 300 × 400 300 × 300 300 × 300 300 × 300 300 × 300
0.801 to 1.00 400 × 400 400 × 400 300 × 400 300 × 400 300 × 400 300 × 400 300 × 300 300 × 300
1.01 to 1.20 400 × 400 400 × 400 400 × 400 400 × 400 300 × 400 300 × 400 300 × 400 300 × 400
1.21 to 1.40 — — 400 × 400 400 × 400 400 × 400 400 × 400 300 × 400 300 × 400
1.41 to 1.60 — — — — 400 × 400 400 × 400 400 × 400 400 × 400
1.61 to 1.80 — — — — — — 400 × 400 400 × 400
1.81 to 2.00 — — — — — — 400 × 400 400 × 400
This provision includes a table — formatting is preserved from the source; refer to the official code for the authoritative layout.
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Code text is reproduced for reference from the Ontario Building Code (O. Reg. 163/24, 2024 Building Code Compendium). This page is provided for general information and is not an official copy. Always verify requirements against the official Ontario Building Code and confirm with your local building department.