Chimneys, Fireplaces & Fire Ratings
Chimney caps, height requirements, flue liners, fire brick, refractory mortar, fire walls, and masonry fire ratings.
- State chimney height requirements above the roofline
- Explain chimney cap and flue liner functions and materials
- Describe fire brick properties and refractory mortar use
- Identify masonry fire wall construction and fire rating requirements
Lección 1
Chimney Height, Caps & Flue Liners
Chimney Height Requirements
The height of a chimney above the roofline is critical for proper draft and fire safety. According to Canadian building codes, the top of the chimney must extend at least 3 feet (900 mm) above the point where it exits the roof and must be at least 2 feet (600 mm) higher than any portion of the roof or adjacent structure within 10 feet (3 m) horizontally.
These height requirements ensure that the chimney generates sufficient draft (upward airflow) to safely exhaust combustion gases and that sparks cannot reach adjacent roofing materials.
Exam Fact
The 3-2-10 rule for chimney height is a frequently tested topic: 3 feet above the roof, 2 feet above anything within 10 feet. Memorize these three numbers.
Chimney Caps
A chimney cap (also called a rain cap or spark arrestor) is installed on top of the chimney to:
- Prevent rain and snow from entering the flue
- Block downdrafts caused by wind
- Stop sparks from escaping (spark arrestor screen)
- Keep animals and debris out of the flue
Caps are typically made of stainless steel, copper, or galvanized steel. Masonry chimney caps may also include a concrete or stone slab with an overhang and drip edge.
Flue Liners
The flue liner protects the chimney masonry from heat and corrosive combustion gases. Without a liner, heat and acidic condensate would deteriorate the mortar joints and eventually allow gases (including carbon monoxide) to leak through the chimney walls.
| Liner Type | Material | Notes |
|---|---|---|
| Clay tile liner | Fired clay | Most common in new masonry chimneys; sections joined with refractory mortar |
| Stainless steel liner | Flexible or rigid stainless | Used for relining existing chimneys |
| Cast-in-place liner | Lightweight refractory cement | Poured around an inflatable form inside the chimney |
Liner Sizing
The flue liner must be sized to match the appliance it serves. An oversized flue causes poor draft and excessive creosote buildup. An undersized flue restricts airflow and can cause backdrafting of combustion gases into the building.
Chimney Construction Details
- Minimum wall thickness for a masonry chimney is typically 4 inches (nominal) of solid masonry around the flue liner
- A 2-inch clearance must be maintained between the chimney masonry and any combustible materials (framing, sheathing)
- The space between the chimney and combustible framing is filled with non-combustible insulation (firestop)
- Each appliance (fireplace, furnace, water heater) should have its own separate flue
The 3-2-10 rule governs chimney height: 3 feet above the roof, 2 feet above any structure within 10 feet. The flue liner protects chimney masonry from heat and corrosive gases. Maintain a 2-inch clearance between the chimney and all combustible materials.