Code of practice for design and construction of flues and chimneys for domestic heating appliances
1962 Edition

Overview of IS 1649 Scope

• Defines technical parameters for the design and erection of flues and chimneys.
• Excludes contractual or administrative provisions.
• Clause 2.0 provides definitions for terms related to flues and chimneys (refer to Fig. 1).
• Clause 0.6 clarifies that compliance is based on measured or calculated final values.
• Appendix A details flue size and chimney height requirements for particular appliances (see Clauses 1.2 and 5.8.5).

Appendix A Highlights

For full details, consult Appendix A of IS 1649.

Flue Design Process Flowchart

flowchart TD
    A[Identify Appliance Type] --> B[Calculate Flue Dimension]
    B --> C[Determine Chimney Height]
    C --> D[Design per IS 1649 Standards]
    D --> E[Verify Compliance (Clause 0.6)]

This section ensures safe and effective flue and chimney designs conforming to IS 1649.

Terminology & Key Definitions in IS 1649

Important Terms (Clause 2.3)

• Core: A soft material sack inserted inside the flue, progressively raised during construction.
• Coring: The act of clearing mortar debris from within the flue using a core.
• Cripple: A board placed to prevent mortar from falling inside the flue, moved upward as masonry progresses.
• Grip Coat: Base coat applied prior to vitreous enamel finishes.
• Pargeting: A smooth mortar rendering applied to flue surfaces.
• Rendering: Application of mortar or plaster on masonry surfaces.
• Spalling: Fragmentation or chipping of materials.

Dimensional Allowances (Clause 4.2)

• Tolerances of ±3 mm in cross-sectional dimensions.
• For square bases, diagonal dimensions must not vary more than ±6 mm.

Terminology Summary Table

Uniform terminology facilitates consistent understanding and quality assurance in chimney construction.

Essential Requirements in IS 1649

• Dimensional Tolerances (Clause 4.2):

  • Cross-sectional dimensions permitted variation: ±3 mm
  • For square bases, diagonal equality within ±6 mm

• Chimney Pot Specifications (Clause 4.5):

  • Must comply with Appendix C requirements

• Flue Size & Height (Clause 1.2 and Appendix A):

  • Refer to Appendix A for appliance-specific dimensions and heights

Dimensional Tolerance Table

Notes:

• The code aligns with Indian building norms and international standards.
• Always verify chimney pot sizes and flue dimensions per appliance for safety and performance.

flowchart LR
    A[Appliance Type] --> B[Consult Flue Size & Height (Appendix A)]
    B --> C[Review Chimney Pot Specs (Appendix C)]
    C --> D[Apply Dimensional Tolerances]

For detailed design, consult full IS 1649 appendices.

Materials and Appliance Data per IS 1649

1. Information Required for Design (Clause 3.1)

Design must consider:

• Site exposure and location
• Nearby tall trees and buildings
• Prevailing wind patterns
• Positioning of doors, windows, and openings in relation to fireplaces
• Potential future appliance replacements
• Manufacturer's specifications including:
  • Installation and fixing details
  • Required flue dimensions
  • Required chimney heights
  • Insulation requirements
  • Air inlet and baffle details

2. Flue and Chimney Dimensions (Appendix A, Clauses 1.2 & 5.8.5)

• Dimensions depend on heat output of appliances (see Tables A-2 and A-3).
• Only appliances within defined heat ranges are covered.

Typical Flue Area Calculation Formula

[ \text{Flue Cross-Sectional Area} = \frac{Q}{C \times \sqrt{H}} ] Where:

• (Q) = heat output (kW)
• (C) = constant based on fuel type and chimney efficiency
• (H) = effective chimney height (m)

Example Flue Dimensions

flowchart TD
    A[Gather Manufacturer Data] --> B[Design Flue & Chimney Dimensions]
    B --> C[Select Materials]
    C --> D[Construct Flue and Chimney]
    D --> E[Ensure Adequate Ventilation]
    E --> F[Optimize Chimney Performance]

Always review manufacturer data along with IS 1649 for accurate design.

Chimney Design Considerations in IS 1649

Highlights from Clause 5

• Flue Design (5.1.1):

  • Dimensions and height must match appliance type and intended use.
  • Proper sizing ensures effective draft and smoke removal.

• Pre-design Data (Clause 3.1):

  • Include site exposure, nearby obstructions, wind direction.
  • Position of openings relative to fireplaces.
  • Possible future appliance changes.
  • Manufacturer’s specifications on size, height, insulation, air inlets, and fixing.

• Material Requirements (5.16):

  • Materials should resist high temperature, weathering, and corrosive flue gases.

Draft Pressure Calculation

[ P = C \times H \times \frac{T_i - T_o}{T_i} ] Where:

• (P) = draft pressure (Pa)
• (C) = constant
• (H) = chimney height (m)
• (T_i), (T_o) = absolute temperatures inside and outside chimney (K)

Flue Cross-Sectional Area Recommendations

flowchart TD
    A[Site Assessment] --> B[Data Collection (Clause 3.1)]
    B --> C[Calculate Flue Size & Height (5.1.1)]
    C --> D[Choose Materials (5.16)]
    D --> E[Design Final Chimney and Flue]
    E --> F[Execute Construction]

In summary, integrate site conditions, appliance data, and material durability to ensure safe, efficient chimney design.

Guidelines for Building Flues and Chimneys as per IS 1649

1. Dimensions (Appendix A, Clauses 1.2 & 5.8.5)

• Cross-sectional area and chimney height depend on appliance type and heat output.
• Minimum flue sizes ensure adequate draft; typical minimums start at 150 x 150 mm for small stoves.
• Chimney height above roof minimum is 3 meters or as appliance demands.

2. Design Requirements

• Fire safety: Use non-combustible materials; maintain clearance from flammable items.
• Structural integrity: Must resist wind and thermal stresses.
• Thermal insulation: Prevent heat loss and condensation.
• Waterproofing: Protect against rain infiltration.
• Condensation control: Use proper lining and maintain draft.

3. Flue Area Formula

[ A = \frac{Q}{C \times \sqrt{H}} ] Where:

• (A) = flue cross-sectional area (m²)
• (Q) = heat output (kW)
• (C) = constant based on fuel and appliance
• (H) = chimney height (m)

Example Flue Sizes

flowchart TD
    A[Heat Output] --> B[Determine Flue Area]
    B --> C[Select Flue Dimensions]
    C --> D[Define Chimney Height]
    D --> E[Check Fire Safety and Structural Strength]
    E --> F[Add Thermal Insulation and Waterproofing]
    F --> G[Proceed with Construction]

Refer to IS 1649 Appendix A for specific appliance-based sizing details.

Handling and Storage Requirements for Masonry Materials (IS 1649)

Key Provisions (Clause 7.1)

• Masonry materials must comply with related IS standards (e.g., IS 1077 for bricks, IS 2185 for concrete blocks).
• Precast blocks must be thoroughly cured before transportation.
• Materials should be stored on clean, dry, and level ground to avoid contamination.
• Avoid exposure to excessive moisture and direct sunlight.
• Handle carefully to prevent damage such as chipping or cracking.

Storage Guidelines

• Stack bricks/blocks in even layers up to 1.5 m height for stability.
• Ensure air circulation between stacks to control moisture.
• Store cement in moisture-resistant bags, off the floor, and away from walls.

Storage Summary Table

Additional Notes

• Follow IS 456 curing requirements.
• Minimum 7-day curing before firing flues (Clause 6.1.k).

flowchart TD
    A[Receive Materials] --> B[Verify Curing]
    B -->|Adequate| C[Store on Dry, Level Surface]
    B -->|Not Adequate| D[Continue Curing]
    C --> E[Stack Uniformly, Max Height 1.5m]
    E --> F[Protect from Moisture and Sunlight]
    F --> G[Use as Scheduled]

Proper handling maintains material quality and structural soundness during construction.

Construction and Bonding Guidelines in IS 1649

The standard references appropriate Indian Standards for masonry and concrete construction.

Key Points:

• Clause 8.1: Follow IS codes such as:
  • Brick masonry: IS 2212
  • Stone masonry: IS 1597
  • Concrete construction: IS 456
• Clause 3.2: Provide comprehensive drawings and instructions to masons for correct bonding.

Common Bond Types (from IS 2212 & IS 1597):

• Stretcher Bond: Bricks laid lengthwise; ideal for half-brick thick walls.
• English Bond: Alternating courses of headers and stretchers; strong and widely used.
• Flemish Bond: Each course alternates headers and stretchers.

Additional Details:

• Ensure proper overlap to avoid aligned vertical joints.
• Use mortar as per IS 2250, typically a 1:6 cement-sand ratio for bricks.
• Maintain uniform joint thickness of approximately 10 mm.

flowchart LR
    A[Design & Drawings] --> B[Material Selection]
    B --> C[Choose Bond Type]
    C --> D[Execute Construction]
    D --> E[Quality Assurance]

IS 1649 mandates adherence to relevant IS standards for bonding and construction to ensure durability and safety.

Damp-proof and Acoustic Insulation Provisions in IS 1649

Specifications (Clauses 9.1, 8.10.1, 5.4, 4.1)

• Prepare mortar beds flush and even (9.1).
• Protect insulation courses with boards when exposed to prevent damage.
• Prevent mortar penetration or fractures in insulation layers.
• Cast in-situ concrete withes integrally with external walls to maintain continuity (8.10.1).
• Follow proper detailing to prevent moisture ingress through walls (5.4).
• Use materials conforming to relevant IS standards for masonry and concrete blocks (4.1).
• Damp-proof courses and flashings must comply with these standards.

Typical Damp-proof Course Materials

Installation Tips

• Position DPC at plinth level, above ground to prevent rising damp.
• Ensure continuous horizontal barrier without gaps.
• Overlap joints by minimum 75 mm.

flowchart TD
    A[Prepare Mortar Bed] --> B[Install Damp-proof Course]
    B --> C[Protect Insulation if Exposed]
    C --> D[Build Masonry on DPC]
    D --> E[Cast Concrete Withes Integrally]

These measures ensure effective protection against moisture and noise.

Work Procedures at Chimney and Flue Tops as per IS 1649

1. Preliminary Data (Clause 3.1)

Provide detailed information on:

• Site exposure and surroundings
• Nearby trees or tall structures
• Prevailing wind directions
• Location of doors/windows relative to heating appliances
• Potential future appliance modifications
• Manufacturer details including fixing, flue size, chimney height, insulation, air inlets, and baffles

2. Flue Size and Chimney Height (Appendix A)

• Dimensions vary with appliance type to ensure efficient evacuation of combustion gases.
• Minimum cross-sectional areas and chimney heights are specified for adequate draft.

3. General Requirements

• Flues must ensure fire safety, structural soundness, thermal insulation, and waterproofing.
• Design must minimize condensation through appropriate materials and sizing.

Draft Calculation Formula

[ Q = A \times V ] Where:

• (Q) = volumetric flow rate of flue gases (m³/s)
• (A) = cross-sectional area of flue (m²)
• (V) = flue gas velocity (m/s)

Sample Flue Dimensions for Domestic Appliances

Refer to Appendix A for comprehensive tables.

flowchart TD
    A[Appliance] --> B[Manufacturer Specifications]
    B --> C[Determine Flue Dimensions]
    B --> D[Determine Chimney Height]
    B --> E[Design Insulation and Air Inlets]
    C & D & E --> F[Finalize Chimney Design]
    F --> G[Ensure Safe Draft and Combustion]

Summary: Detailed site and appliance data combined with correct sizing ensure safe chimney operation.

Maintenance and Sweeping Guidelines from IS 1649

Key Points (Clauses 5.23.5 & 5.18)

• Access Openings:

  • Provided at base and bends for insertion of cleaning brushes.
  • Sized to accommodate cleaning equipment.
  • Equipped with airtight doors to prevent leakage.
  • Positioned to allow complete sweeping of the flue.

• Soot Doors:

  • Required for maintenance access (Clause 5.18).
  • Must be airtight and easily operable.

Operational Testing (Clause 12.4)

• Burn materials like old gunny bags or paper in the hearth.
• Smoke should exit freely without obstruction under normal weather conditions.

Maintenance Design Inputs (Clause 3.1)

• Account for site exposure, nearby obstructions, wind direction.
• Consider door/window positioning relative to fireplaces.
• Include future appliance modifications and manufacturer data.

Maintenance Features Table

flowchart LR
    A[Chimney Design] --> B[Provide Access Openings]
    B --> C[Install Soot Doors at Key Points]
    C --> D[Enable Complete Flue Sweeping]
    A --> E[Conduct Operational Testing]
    E --> F[Burn Test]
    F --> G[Verify Smoke Flow]
    A --> H[Incorporate Site and Appliance Data]
    H --> I[Plan for Maintenance]

Ensure airtight access points for effective cleaning and safe operation.

Fire Protection and Flue Specifications under IS 1649

References

• Fire safety requirements align with IS 1645-1960 (Code of Practice for Fire Safety of Buildings - Chimneys, Flues, Flue Pipes, Hearths).
• Clauses 5.2 and 5.11.1 mandate compliance with IS 1645 fire protection norms.
• Appendix A (Clauses 1.2 and 5.8.5) specifies flue sizes and heights for various appliances.

Flue Dimensions for Fire Safety

Dimensions depend on fuel type and appliance capacity.

Fire Safety Guidelines

• Maintain minimum clearances from combustible materials as per IS 1645.
• Use non-flammable materials in flue construction.
• Ensure adequate ventilation to prevent gas buildup.
• Conduct regular inspections and maintenance to avoid fire risks.

flowchart LR
    A[Appliance] --> B[Select Flue Size & Height (IS 1649 Appendix A)]
    B --> C[Comply with Fire Safety (IS 1645)]
    C --> D[Maintain Clearance & Use Proper Materials]
    D --> E[Perform Regular Inspection & Maintenance]

For detailed fire safety design, refer to IS 1645 alongside IS 1649.

IS 1649: Domestic Appliances Scope and Flue Specifications

1. Appliance Coverage (Clause 1.2 & Appendix A)

• Appliances included are enumerated in Appendix A.
• Flue and chimney guidelines apply only if appliance heat output falls within limits in Appendix A-2 and A-3.

2. Flue Sizing and Height (Clauses 5.8.3 & 5.8.5)

• For appliances with heat output exceeding 10,000 kcal/h, chimney height must be designed to provide sufficient draft.
• Flue internal dimensions must comply with Appendix A specifications.

Flue Design Parameters

Draft Calculation Formula

[ D = C \sqrt{2gH \frac{T_i - T_o}{T_o}} ] Where:

• (D) = draft pressure (Pa)
• (C) = discharge coefficient (~0.65)
• (g) = gravity acceleration (9.81 m/s²)
• (H) = chimney height (m)
• (T_i), (T_o) = absolute internal and external temperatures (K)

flowchart TD
    A[Identify Appliance] --> B[Check Heat Output]
    B -->|≤10,000 kcal/h| C[Use Standard Flue Sizes]
    B -->|>10,000 kcal/h| D[Custom Flue Design]
    D --> E[Calculate Draft]
    E --> F[Determine Chimney Height]

Summary: Use Appendix A for appliance listings and flue dimensions; design chimneys for larger appliances to ensure adequate draft.

IS 1649: Clay Flue Lining Requirements (Appendix B, Clause 4.4)

Specifications

• Minimum wall thickness: 2 cm
• Length of straight units: 30–40 cm
• Curved units have end angles of either 22½° or 37½° (refer Fig. 4D)
• Maximum straightness deviation: 6 mm (using straight edge, Fig. 5)
• Maximum deviation from 90° edge angles: 6 mm (Fig. 7)
• Maximum deviation from wall angles: 6 mm at any point (Fig. 6)

Material Characteristics

• Made from fireclay or terracotta
• Must be sound with no visible defects
• Should produce a clear ringing sound when lightly tapped (hammer ≤ 0.15 kg)
• May be vitrified or glazed/un-glazed

Typical Shapes (Fig. 4)

• Square section
• Circular section
• Square or ogee rebates
• Straight and curved units

Specification Summary

flowchart TD
    A[Clay Flue Linings] --> B[Material: Fireclay or Terracotta]
    A --> C[Minimum Wall Thickness: 2 cm]
    A --> D[Straight Units: 30–40 cm Length]
    A --> E[Curved Units: 22½° or 37½° Angles]
    A --> F[Max Deviation ≤ 6 mm]
    F --> F1[From Straightness]
    F --> F2[From Edge Angles]
    F --> F3[From Wall Angles]

These standards ensure consistent quality and fit of clay flue linings.

IS 1649: Chimney Pot Specifications

Material and Quality (Clause 1.1)

• Manufactured from fireclay or terracotta
• Must be sound and free from defects
• Should emit a clear ringing sound when lightly tapped (hammer ≤ 0.15 kg)
• May be vitrified or non-vitrified, glazed or unglazed

Dimensional Tolerances

• Maximum deviation from straightness: 6 mm (Fig. 5)
• Maximum deviation from 90° angle between edges or walls: 6 mm (Figs. 6 & 7)
• Maximum deviation at any point: 6 mm

Shape and Size (Clause 2.1)

• Bottom section matches flue lining dimensions
• For flue linings ≥ 20 cm, pots are tapered from base dimension to circular top with 15 cm internal diameter (Fig. 8A)
• For flue linings < 20 cm, pots may be straight cylindrical (Fig. 8B)

Base Specifications (Clause 3.1)

• Base must be flat and free of indentations or protrusions
• Base must be perpendicular to the pot’s vertical axis

Summary Table

flowchart TB
    A[Flue Lining Size] -->|≥ 20 cm| B[Tapered Chimney Pot]
    A -->|< 20 cm| C[Straight Cylindrical Pot]
    B --> D[Base Matches Flue Section]
    C --> D
    D --> E[Top Diameter = 15 cm (for tapered)]

These specifications ensure proper fit and durability of chimney pots.