The Ontario Building Code | Fireplace Chimneys
9.21.2.5. fireplace Chimneys
(1) The size of a chimney flueserving a masonry fireplace shall be within the allowable range specified in 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)
| Item | Column 1 | Column 2 | Column 3 | Column 4 | Column 5 | Column 6 | Column 7 | Column 8 | Column 9 |
|
| fireplace Opening, m² | Chimney Height, m |
|
|
|
|
|
| |
|
|
| 3.0 to 4.5 | > 4.5 to 5.9 | > 5.9 to 8.9 | > 8.9 to 12 | ||||
|
|
| Flue diameter, mm |
|
|
|
|
|
| |
|
|
| Min. | Max. | Min. | Max. | Min. | Max. | Min. | Max. |
| 1. | Up to 0.150 | 110 | 170 | 100 | 160 | 90 | 150 | 90 | 150 |
| 2. | 0.151 to 0.250 | 150 | 210 | 130 | 190 | 130 | 190 | 120 | 180 |
| 3. | 0.251 to 0.350 | 180 | 240 | 160 | 220 | 150 | 210 | 140 | 200 |
| 4. | 0.351 to 0.500 | 220 | 280 | 200 | 260 | 190 | 250 | 170 | 230 |
| 5. | 0.501 to 0.650 | 260 | 320 | 230 | 290 | 220 | 280 | 200 | 260 |
| 6. | 0.651 to 0.800 | 290 | 350 | 260 | 320 | 240 | 300 | 220 | 280 |
| 7. | 0.801 to 1.00 | 330 | 390 | 290 | 350 | 270 | 330 | 250 | 310 |
| 8. | 1.01 to 1.20 | 360 | 420 | 320 | 380 | 300 | 360 | 270 | 330 |
| 9. | 1.21 to 1.40 | 390 | 450 | 350 | 410 | 330 | 390 | 300 | 360 |
| 10. | 1.41 to 1.60 | 420 | 480 | 380 | 440 | 350 | 410 | 320 | 380 |
| 11. | 1.61 to 1.80 | — | — | 400 | 460 | 370 | 430 | 340 | 400 |
| 12. | 1.81 to 2.00 | — | — | — | — | 400 | 460 | 360 | 420 |
| 13. | 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)
| Item | Column 1 | Column 2 | Column 3 | Column 4 | Column 5 | Column 6 | Column 7 | Column 8 | Column 9 |
|
| fireplace Opening, m² | Chimney Height, m |
|
|
|
|
|
| |
|
|
| 3.0 to 4.5 | > 4.5 to 5.9 | > 5.9 to 8.9 | > 8.9 to 12 | ||||
|
|
| Flue Size, mm |
|
|
|
|
|
| |
|
|
| Min. | Max. | Min. | Max. | Min. | Max. | Min. | Max. |
| 1. | Up to 0.150 | 200 × 200 | 200 × 200 | 100 × 200 | 100 × 200 | 100 × 200 | 100 × 200 | 100 × 200 | 100 × 200 |
| 2. | 0.151 to 0.250 | 200 × 200 | 200 × 200 | 200 × 200 | 200 × 200 | 200 × 200 | 200 × 200 | 200 × 200 | 200 × 200 |
| 3. | 0.251 to 0.350 | 200 × 300 | 200 × 300 | 200 × 200 | 200 × 300 | 200 × 200 | 200 × 200 | 200 × 200 | 200 × 200 |
| 4. | 0.351 to 0.500 | 300 × 300 | 300 × 300 | 200 × 300 | 200 × 300 | 200 × 300 | 200 × 300 | 200 × 200 | 200 × 300 |
| 5. | 0.501 to 0.650 | 300 × 300 | 300 × 400 | 300 × 300 | 300 × 300 | 300 × 300 | 300 × 300 | 200 × 300 | 200 × 300 |
| 6. | 0.651 to 0.800 | 300 × 400 | 300 × 400 | 300 × 300 | 300 × 400 | 300 × 300 | 300 × 300 | 300 × 300 | 300 × 300 |
| 7. | 0.801 to 1.00 | 400 × 400 | 400 × 400 | 300 × 400 | 300 × 400 | 300 × 400 | 300 × 400 | 300 × 300 | 300 × 300 |
| 8. | 1.01 to 1.20 | 400 × 400 | 400 × 400 | 400 × 400 | 400 × 400 | 300 × 400 | 300 × 400 | 300 × 400 | 300 × 400 |
| 9. | 1.21 to 1.40 | — | — | 400 × 400 | 400 × 400 | 400 × 400 | 400 × 400 | 300 × 400 | 300 × 400 |
| 10 | 1.41 to 1.60 | — | — | — | — | 400 × 400 | 400 × 400 | 400 × 400 | 400 × 400 |
| 11. | 1.61 to 1.80 | — | — | — | — | — | — | 400 × 400 | 400 × 400 |
| 12. | 1.81 to 2.00 | — | — | — | — | — | — | 400 × 400 | 400 × 400 |
In Plain Language
Fireplace chimneys have their own flue requirements set out in this article, tailored to the particular venting needs of a wood-burning fireplace.
This is a plain-language summary of the 2012/2017 Ontario Building Code text above, for general understanding only and not a substitute for the Code. Always confirm current requirements against the 2024 edition (O.Reg. 163/24) or a qualified professional before construction.