Preliminary homeowner estimator
Chimney Height Calculator
Enter the measured vertical rise from the roof penetration to the highest nearby roof surface or structure within 3 metres. The estimator compares 900 mm above the penetration with 600 mm above that nearby point.
Your result
Enter a measurement to see the larger of the two preliminary height checks.
Do not use this result as an installation approval
The estimate does not evaluate appliance type, chimney system listing, manufacturer instructions, Ontario amendments, roof geometry, nearby trees, terrain, wind, draft, bracing, structural support, or local-authority requirements. Never climb onto a roof to obtain a measurement unless you are trained and equipped to do so.
How the calculation works
The tool returns the greater of:
- 0.9 m above the point where the chimney contacts the roof; or
- the measured nearby vertical rise plus 0.6 m.
The 3 m horizontal search distance is something you must establish before entering the vertical rise. The calculator does not derive it from roof pitch.
Sources to verify
- Ontario's current Building Code information
- O. Reg. 163/24 adopting the NBC 2020 with Ontario amendments
- NRC archive showing the 900-600-3 m geometry
Use the current applicable code, amendments, listed chimney instructions, and local authority—not an archived document alone—for an actual project.
Need the whole system reviewed?
A termination-height estimate is only one installation detail. Use the readiness checklist or request contact from an independent provider for an appropriate inspection discussion.
Last reviewed: July 23, 2026.