Venting and Chimney Systems

Venting Systems and Chimneys

Chapter Introduction

This chapter covers the fundamental principles, regulatory requirements, and installation procedures related to venting systems for oil-fired appliances. As an oil heating technician, you must master the sizing, installation, inspection, and maintenance of chimneys and vent connectors. This chapter aligns with the requirements of the Canadian Electrical Code, Part I (CE Code) (for related electrical aspects) and CSA B139 (Installation Code for Oil-Burning Equipment), as well as CSA B149.1 (Natural Gas and Propane Installation Code) for general ventilation principles. Specific requirements for oil-fired appliances are primarily governed by CSA B139-19 (Installation Code for Oil-Burning Equipment), with cross-references to CSA B365 (Chimneys, Fireplaces, Appliances, and Vents) for masonry and prefabricated chimneys.

Fundamental Principles of Combustion Venting

Why is a Venting System Necessary?

Oil combustion produces hot gases containing carbon dioxide (CO₂), water vapor (H₂O), nitrogen (N₂) and, under incomplete combustion conditions, carbon monoxide (CO) and soot. These products must be safely exhausted to the outdoors. The venting system has three main functions:

8.Remove combustion products from the dwelling.

9.Create sufficient draft to bring combustion air to the appliance.

10.Protect the structure from high temperatures and corrosion.

Draft: Definition and Calculation

Draft is the pressure difference between the inside of the chimney and the ambient outdoor air. It is caused by the temperature difference (and therefore density difference) between the hot gases in the chimney and the cold outdoor air. Draft is measured in pascals (Pa) or inches of water column (in. w.c.). The conversion: 1 in. w.c. = 249 Pa.

The theoretical (natural) draft can be estimated using the simplified formula:

Draft (Pa) = H × (ρ_air − ρ_gas) × g

Where:

H = effective chimney height (m)

ρ_air = density of outdoor air (kg/m³)

ρ_gas = density of flue gases at average temperature (kg/m³)

g = gravitational acceleration (9.81 m/s²)

In practice, the required draft for an oil-fired appliance typically ranges between −5 Pa and −25 Pa (negative draft, meaning a depression in the chimney). Excessive draft (greater than −40 Pa) can cause unstable combustion and appliance overheating. Insufficient draft (less than −5 Pa) can cause flue gas spillage into the room.

Factors Affecting Draft

Factor	Effect on Draft	Explanation
Chimney height	↑ height = ↑ draft	The taller the column of hot gases, the greater the pressure difference
Gas temperature	↑ temperature = ↑ draft	Hotter gases are less dense, therefore lighter
Outdoor temperature	↓ outdoor temp. = ↑ draft	Cold air is denser, increasing the density difference
Connector diameter	↑ diameter = ↓ draft (generally)	A wider connector cools the gases more quickly
Horizontal length	↑ length = ↓ draft	Horizontal sections increase resistance and cooling
Number of elbows	↑ elbows = ↓ draft	Each elbow adds resistance to gas flow

Types of Venting Systems

Masonry Chimneys

Masonry chimneys are constructed of brick, concrete block, or stone, with a liner (flue lining) made of refractory clay or corrosion-resistant material. Requirements are specified in CSA B365.

Key Requirements for Masonry Chimneys:

The liner must have a minimum thickness of 15 mm (5/8 in.) for refractory clay.

The space between the liner and the masonry must be a minimum of 20 mm (3/4 in.).

The chimney must rest on a foundation capable of supporting its weight.

The chimney top must extend at least 900 mm (3 ft) above the roof penetration point, or at least 600 mm (2 ft) above any obstacle within a 3 m (10 ft) radius.

Prefabricated (Metal) Chimneys

Prefabricated chimneys are certified systems per ULC S629 (metal chimneys for solid and liquid fuel appliances). They consist of double or triple wall sections with an insulated air space.

Key Requirements:

Follow the manufacturer's installation instructions.

Maintain minimum clearances to combustible materials (typically 50 mm (2 in.) for insulated double-wall chimneys).

Use only compatible components from the same manufacturer.

Never modify or penetrate a prefabricated chimney.

Single-Wall Metal Flue Pipes (Connector Pipes)

The flue pipe (or connector pipe) connects the appliance to the chimney. It must be made of galvanized steel (minimum thickness of 0.5 mm (24 gauge)) or stainless steel for high-temperature or corrosive applications.

Flue Pipe Installation Rules:

The maximum horizontal length is 75% of the vertical chimney height (the 75% rule).

The upward slope must be at least 25 mm per metre (1/4 in. per foot) toward the chimney.

Elbows must be limited to a maximum of two 90° elbows (or equivalent) between the appliance and the chimney.

The pipe must be supported at each joint and each elbow.

Joints must be assembled with screws and sealed with heat-resistant mastic (minimum 400 °C).

Forced-Draft Venting Systems (Power Venters)

Power venter systems (mechanical exhaust) use a fan to expel combustion products. They are certified according to ULC S636 (venting systems for gas appliances) or the specific requirements of CSA B139 for oil.

Advantages:

No conventional chimney required.

Can be installed through exterior walls.

Increased efficiency (less heat loss).

Requirements:

The system must be certified for use with oil.

The termination must be located at least 1 m (3 ft) from any building opening (window, door, air inlet).

The termination must be at least 300 mm (12 in.) above ground level or anticipated snow accumulation.

A safety switch must shut off the oil supply in the event of fan failure.

Sizing of Chimneys and Connectors

General Sizing Rule

Sizing a chimney for an oil-fired appliance must be based on:

63.The appliance input rating (kW or BTU/h).

64.The chimney height.

65.The flue gas temperature.

66.The appliance type (natural draft or forced draft).

The rule of thumb: the cross-sectional area of the chimney must be at least equal to the area of the appliance flue collar (the combustion product outlet). For a typical residential oil-fired appliance of 100,000 BTU/h (29.3 kW), a 150 mm (6 in.) diameter connector is generally sufficient with a 150 mm (6 in.) or 200 mm (8 in.) chimney.

Quick Sizing Reference Table

Appliance Input (kW)	Minimum Flue Pipe Diameter	Minimum Chimney Diameter (Masonry)
Up to 30 kW (100,000 BTU/h)	150 mm (6 in.)	150 mm (6 in.)
30 to 60 kW (100,000 to 200,000 BTU/h)	200 mm (8 in.)	200 mm (8 in.)
60 to 100 kW (200,000 to 350,000 BTU/h)	250 mm (10 in.)	250 mm (10 in.)
Over 100 kW	Calculate per CSA B139	Calculate per CSA B139

Combined Cross-Section Calculation

When multiple appliances are connected to the same chimney, the combined cross-section must be calculated. CSA B139 requires that the chimney cross-section be at least equal to the sum of the individual flue pipe cross-sections, with a 25% reduction factor for forced-draft appliances (since they control their venting better).

Example: Two 30 kW appliances, each with 150 mm connectors (area = π × r² = 3.1416 × 75² = 17,671 mm² each). Total area = 35,342 mm². The chimney must have a cross-section of at least 35,342 mm², which corresponds to a diameter of √(35,342 / π) × 2 = 212 mm (rounded up to 225 mm or 9 in.).

The 75% Rule (Horizontal Length)

The total length of horizontal sections of a flue pipe must not exceed 75% of the vertical chimney height.

Example: Chimney height of 6 m. Maximum horizontal length = 6 × 0.75 = 4.5 m.

Installation and Installation Requirements

Clearances to Combustible Materials

Minimum clearances are essential to prevent fires. They are specified in CSA B139 and CSA B365.

Component	Minimum Clearance to Combustibles
Single-wall flue pipe	450 mm (18 in.)
Double-wall (insulated) flue pipe	150 mm (6 in.)
ULC S629 certified prefabricated chimney	50 mm (2 in.)
Masonry chimney (exterior surface)	50 mm (2 in.)
Oil-fired appliance (surface)	450 mm (18 in.) (depending on model)

Wall and Floor Penetrations

When a flue pipe passes through a combustible wall or floor, it must be protected by a protective sleeve or a certified penetration. The rules:

For single-wall pipe: use a masonry thimble or a heat shield with a minimum clearance of 450 mm (18 in.).

For double-wall pipe: the clearance can be reduced to 150 mm (6 in.) with appropriate protection.

The penetration must be sealed with fire-resistant caulking (fire resistance rating of at least 1 hour).

Chimney Termination

The termination (top) of the chimney must:

Be fitted with a cap to prevent the entry of rain, snow, and animals.

Extend at least 900 mm (3 ft) above the roof penetration point.

Be at least 600 mm (2 ft) above any obstacle (tree, wall, other roof) within a 3 m (10 ft) radius.

Have a spark arrestor screen (mesh) with openings no larger than 12 mm (1/2 in.) to prevent bird entry.

Connecting Multiple Appliances

When multiple appliances are connected to the same chimney:

Each appliance must have its own individual flue pipe.

The pipes must enter the chimney at different levels (minimum vertical spacing of 300 mm).

The pipes must not enter the chimney at the same level (to avoid draft interference).

A damper may be required on each pipe to control draft.

Inspection and Maintenance

Chimney Inspection Procedure

101.Exterior visual inspection: check the condition of the cap, joints, and masonry (cracks, spalling).

102.Interior inspection: use a mirror and flashlight to check the condition of the liner (cracks, displacement, soot buildup).

103.Draft measurement: use a manometer to measure the draft at the chimney inlet (at the appliance flue collar).

104.Clearance verification: measure the distances to combustible materials.

105.Tightness check: use a smoke pencil or artificial smoke to detect leaks.

Signs of Common Problems

Problem	Visible Sign	Probable Cause
Spillage	Oil odors, soot traces around the appliance	Insufficient draft, blocked chimney
Condensation	Water droplets in the pipe, rust	Flue gas temperature too low, oversized chimney
Creosote (soot)	Black sticky deposit in the pipe	Incomplete combustion, temperature too low
Masonry cracks	Visible cracks from the outside	Thermal expansion, freeze-thaw cycles, excessive draft

Recommended Maintenance Frequency

Annual inspection: mandatory before each heating season.

Cleaning: based on soot buildup (generally annual for oil).

Comprehensive inspection: every 5 years by a qualified technician (with inspection camera if necessary).

Regulatory Requirements and Codes

CSA B139-19 (Installation Code for Oil-Burning Equipment)

This standard is the primary reference for the installation of oil-fired appliances and their venting systems. Key points:

Article 6.4: Requirements for chimneys and flue pipes.

Article 6.5: Sizing of venting systems.

Article 6.6: Clearances to combustible materials.

Article 6.7: Connection of appliances to chimneys.

CSA B365 (Chimneys, Fireplaces, Appliances, and Vents)

This standard covers the installation of masonry and prefabricated chimneys, as well as flue pipes. Key points:

Article 4.2: Requirements for masonry chimneys.

Article 4.3: Requirements for prefabricated chimneys.

Article 5.1: Installation of flue pipes.

Canadian Electrical Code, Part I (CE Code)

For the electrical aspects of venting systems (fans, safety switches, alarms):

Rule 8-200: General requirements for the installation of electrical equipment.

Rule 26-700: Installation of motors and controls.

Other Relevant Standards

CSA B140.0: Oil-fired appliances (general requirements).

CSA B140.2.1: Vaporizing oil burners.

ULC S629: Prefabricated metal chimneys.

ULC S636: Venting systems for gas appliances (reference for power venters).

Pitfalls to Avoid

136.Confusing the standards: CSA B139 applies to oil, CSA B149.1 applies to gas. Do not apply the requirements of one to the other without verification.

137.Neglecting the 75% rule: Excessive horizontal length is a common cause of spillage. Always calculate the horizontal length / vertical height ratio.

138.Forgetting the 450 mm clearance for single-wall pipes. This clearance is often incorrectly reduced.

139.Using aluminum pipe for the connector. Aluminum is not resistant to corrosion from oil combustion products. Use galvanized or stainless steel.

140.Ignoring condensation in oversized chimneys. A chimney that is too wide cools the gases and causes acidic condensation that corrodes the pipe.

141.Not checking the draft after installation. The draft must be measured and adjusted (with a damper or draft regulator) to fall within the range recommended by the appliance manufacturer.

142.Connecting an appliance to an unlined chimney: A masonry chimney without a liner must not be used for an oil-fired appliance.

143.Forgetting the chimney cap: A cap is mandatory to prevent the entry of water and animals.

144.Not respecting power venter termination requirements: The minimum distance of 1 m (3 ft) from building openings is often misinterpreted.

145.Confusing positive and negative draft: Draft is a depression (negative pressure) in the chimney. Positive draft indicates spillage.

Summary

Draft is the driving force that exhausts combustion products. It depends on chimney height, gas temperature, and outdoor temperature.

Masonry chimneys must have a liner and comply with the requirements of CSA B365.

Prefabricated chimneys must be certified to ULC S629 and installed according to the manufacturer's instructions.

Flue pipes must be galvanized or stainless steel, with an upward slope of 25 mm/m and a maximum horizontal length of 75% of the vertical height.

Clearances to combustible materials are critical: 450 mm for single-wall pipes, 50 mm for certified prefabricated chimneys.

Sizing must account for the appliance input, chimney height, and flue gas temperature.

CSA B139 is the primary standard for the installation of oil-fired appliances and their venting systems.

Annual inspection is mandatory and must include draft measurement, clearance verification, and chimney condition assessment.

Power venters (forced draft) offer an alternative to conventional chimneys but must comply with strict termination requirements.

Condensation is a major problem in oversized or poorly insulated chimneys.

Spillage is a serious health hazard (CO poisoning) and must be addressed immediately.

Self-Assessment Questions

161.What is the recommended draft for a typical residential oil-fired appliance?

162.What is the maximum horizontal length of a flue pipe for a chimney 8 m in height?

163.What is the minimum clearance to combustible materials for a single-wall flue pipe?

164.Which standard governs the installation of oil-fired appliances in Canada?

165.What is the minimum slope of a horizontal flue pipe?

166.What are the three main factors that affect chimney draft?

167.What is the minimum distance between a power venter termination and a window?

168.What material must never be used for an oil flue pipe?

169.What is the minimum height a chimney must extend above the roof?

170.What is the 75% rule and how does it apply?

(Answers: 1. −5 to −25 Pa ; 2. 6 m (8 × 0.75) ; 3. 450 mm ; 4. CSA B139 ; 5. 25 mm/m ; 6. Height, gas temperature, outdoor temperature ; 7. 1 m ; 8. Aluminum ; 9. 900 mm ; 10. The horizontal length must not exceed 75% of the vertical chimney height.)