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

IS 1649: Scope Summary

• Scope: Covers technical provisions for design and construction of flues and chimneys.
• Exclusions: Does not cover all contractual provisions.
• Definitions: Clause 2.0 defines key terms related to flues/chimneys (see Fig. 1 in the code).
• Compliance: Clause 0.6 states compliance is based on final observed or calculated values.
• Appendix A: Provides size and height of flues for specific appliances (Clauses 1.2 & 5.8.5).

Key Specifications (from Appendix A)

Note: Refer to IS 1649 Appendix A for detailed tables.

Conceptual Flow of Flue Design Scope

flowchart TD
    A[Appliance Type] --> B[Determine Flue Size]
    B --> C[Determine Flue Height]
    C --> D[Design & Construction per IS 1649]
    D --> E[Check Compliance (Clause 0.6)]

This scope ensures safe, efficient flue/chimney design per IS 1649 technical provisions.

IS 1649: Terminology & Key Specifications

Key Definitions (Clause 2.3)

• Core: Soft material sack fitted inside flue, drawn up as work proceeds.
• Coring: Using a core to clear flue interiors from mortar droppings.
• Cripple: Board to prevent mortar dropping inside flue, moved up as work progresses.
• Grip Coat: Undercoat for vitreous enamels.
• Pargeting: Smooth rendering on flue faces.
• Rendering: Mortar/plaster coats applied on brick/concrete/stone.
• Spalling: Breaking off in fragments/chips.

Dimensional Tolerances (Clause 4.2)

• Cross dimension tolerance: ±3 mm.
• Diagonal tolerance for square bases: ±6 mm.

Summary Table

This terminology ensures uniform understanding and quality control in chimney/flue construction per IS 1649.

IS 1649: General Requirements - Key Points

• Tolerance in Dimensions (Clause 4.2):

  • Maximum permissible tolerance in cross dimension: ±3 mm
  • For square bases, diagonals must be equal within ±6 mm

• Chimney Pots (Clause 4.5):

  • Must conform to specifications in Appendix C

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

  • Refer to Appendix A for detailed size and height specifications based on appliance type (not fully provided here).

Summary Table: Dimensional Tolerances

Notes:

• The standard aligns with Indian building practices and international coordination.
• For detailed flue sizes and chimney pot specs, consult Appendices A and C respectively.
• Always verify chimney pot dimensions and flue requirements per appliance for safety and functionality.

flowchart LR
    A[Appliance Type] --> B[Flue Size & Height (Appendix A)]
    B --> C[Chimney Pot Specifications (Appendix C)]
    C --> D[Dimensional Tolerances (±3 mm, ±6 mm)]

For precise design, always refer to the full IS 1649 appendices and clauses.

IS 1649: Materials, Appliances, and Components – Key Points

1. Materials and Appliances Information (Clause 3.1)

For proper design and construction, detailed info must be provided on:

• Locality & exposure of site and chimneys
• Proximity to trees and tall buildings
• Prevailing wind direction
• Position of doors, windows, and openings relative to fireplaces
• Future appliance changes possibility
• Manufacturer details including:
  • Fixing and setting requirements
  • Required flue size
  • Required chimney height
  • Insulation needs
  • Air inlets and baffles
  • Other design-relevant info

2. Size and Height of Flues (Appendix A, Clauses 1.2 & 5.8.5)

• Flue and chimney dimensions depend on appliance heat range (see Tables A-2, A-3).
• Only appliances within specified heat limits are covered.

Typical Flue Sizing Formula (from general practice aligned with IS 1649):

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

Where:

• (Q) = Heat output of appliance (kW)
• (C) = Constant depending on fuel type and chimney efficiency
• (H) = Effective chimney height (m)

Summary Table (Indicative)

flowchart TD
    A[Appliance Manufacturer Data] --> B[Design of Flue Size & Chimney Height]
    B --> C[Material Selection]
    C --> D[Construction]
    D --> E[Proper Ventilation & Air Inlets]
    E --> F[Efficient Chimney Function]

Note: Always consult manufacturer data and IS 164

IS 1649: Design Considerations for Chimneys

Key Points from Clause 5 (Design Considerations)

• 5.1.1 Flue Design:

  • Cross-sectional area and vertical height must suit the flue’s purpose and appliance type.
  • Proper sizing ensures efficient draft and smoke evacuation.

• Clause 3.1 (Pre-design Data):
  Essential information to be collected includes:

  • Locality exposure, nearby trees/buildings
  • Prevailing wind direction
  • Location of openings (doors/windows) relative to fireplaces
  • Future appliance changes
  • Manufacturer’s data: flue size, chimney height, insulation, air inlets, fixing details.

• Clause 5.16 (Material Selection):
  Materials must withstand high temperatures, weather, and corrosive gases.

Typical Design Formula (Draft Calculation)

[ \text{Draft} (P) = C \times H \times \frac{T_i - T_o}{T_i} ]

Where:

• (P) = draft pressure (Pa)
• (C) = constant (depends on units)
• (H) = chimney height (m)
• (T_i) = absolute temperature inside flue (K)
• (T_o) = outside air temperature (K)

Flue Cross-Sectional Area Guidelines (from appliance manufacturer or IS recommendations)

flowchart TD
    A[Site Survey] --> B[Collect Data (Clause 3.1)]
    B --> C[Determine Flue Size & Height (5.1.1)]
    C --> D[Material Selection (5.16)]
    D --> E[Design Chimney & Flue]
    E --> F[Construction & Installation]

Summary: Design chimneys by integrating site data, appliance specs, and material durability, ensuring flue cross-section and height match the draft requirements for safe, efficient operation.

IS 1649: Construction of Flues and Chimneys – Key Points

1. Flue and Chimney Size & Height (Appendix A, Clauses 1.2 & 5.8.5)

• Flue cross-sectional area and chimney height depend on the type and heat output of domestic appliances.
• Minimum cross-sectional area ensures adequate draft; typical sizes range from 150 mm x 150 mm for small stoves to larger sizes for bigger appliances.
• Minimum chimney height above roof: 3 meters or as per appliance requirement to ensure proper draft and dispersion.

2. Design Considerations

• Fire safety: Use fire-resistant materials; maintain safe clearances from combustible materials.
• Structural strength: Chimneys must withstand wind loads and thermal stresses.
• Thermal insulation: Prevent heat loss and condensation inside flues.
• Waterproofing: Protect chimney from rain ingress to avoid deterioration.
• Condensation prevention: Proper flue lining and adequate draft.

3. Typical Flue Area Formula

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

• (A) = Flue cross-sectional area (m²)
• (Q) = Heat output (kW)
• (C) = Constant depending on fuel type and appliance
• (H) = Height of chimney (m)

Summary Table: Typical Flue Sizes (Example)

flowchart TD
    A[Appliance Heat Output] --> B[Determine Flue Area]
    B --> C[Select Flue Size]
    C --> D[Determine Chimney Height]
    D --> E[Check Fire Safety & Structural Strength]
    E --> F[Apply Thermal Insulation & Waterproofing]
    F --> G[Construct Flue & Chimney]

Note: Refer to IS 1649 Appendix A for detailed tables and appliance-specific sizes.

IS 1649: Handling and Storage of Masonry Materials

Key Specifications (Clause 7.1)

• Masonry materials must be handled and stored as per relevant IS codes (e.g., IS 1077 for bricks, IS 2185 for concrete blocks).
• Precast blocks must be adequately cured before transport to ensure strength and durability.
• Materials should be stacked on a clean, dry, and level surface to prevent contamination and damage.
• Avoid exposure to excess moisture or direct sunlight to maintain material integrity.
• Handle with care to prevent chipping, cracking, or deformation.

Important Points for Storage:

• Stack bricks/blocks in uniform layers, with height not exceeding 1.5 m to prevent instability.
• Allow air circulation between stacks for moisture control.
• Store cement in dry, moisture-proof bags, off the ground, and away from walls.

Reference Table (Typical Storage Guidelines):

Additional Notes:

• Follow IS 456 for curing periods when cement is used.
• Ensure minimum 7 days curing before firing flues (Clause 6.1.k).

flowchart TD
    A[Receive Masonry Materials] --> B[Check Curing Status]
    B -->|Adequate| C[Store on Dry, Level Surface]
    B -->|Inadequate| D[Continue Curing]
    C --> E[Stack Uniformly, Max Height 1.5m]
    E --> F[Protect from Moisture & Sunlight]
    F --> G[Use as per Construction Schedule]

This ensures material quality and structural integrity during construction.

IS 1649: Construction Details and Bonding - Key Points

IS 1649 primarily refers to relevant Indian Standards for construction details and bonding, emphasizing compliance with masonry, stone, and concrete standards.

Key Guidelines:

• Clause 8.1: Construction must follow relevant IS codes, e.g.,
  • Brick masonry: IS 2212
  • Stone masonry: IS 1597
  • Concrete construction: IS 456
• Clause 3.2: Provide detailed drawings and instructions to masons for correct bonding and construction.

Typical Bonding Specifications (from IS 2212 & IS 1597):

• Brick Masonry Bonds:
  • Stretcher Bond: Bricks laid lengthwise, suitable for half-brick thick walls.
  • English Bond: Alternate courses of headers and stretchers; strong and commonly used.
  • Flemish Bond: Each course consists of alternate headers and stretchers.

Construction Details:

• Bonding: Ensure proper overlap of bricks/stones to avoid vertical joints lining up.
• Mortar: Use mortar as per IS 2250, typically cement-sand mix 1:6 for brick masonry.
• Joints: Keep joints uniform, thickness 10 mm.

flowchart LR
    A[Planning & Drawings] --> B[Material Selection]
    B --> C[Bond Type Selection]
    C --> D[Construction Execution]
    D --> E[Quality Check & Compliance]

Summary: IS 1649 mandates adherence to relevant IS codes for masonry bonding and construction details, emphasizing proper planning, bonding patterns, and quality control.

IS 1649: Provision of Damp-proof and Sound Insulation Courses

Key Specifications (Clauses 9.1, 8.10.1, 5.4, 4.1)

• Bed Preparation (9.1):

  • Bed must be flushed with mortar to form an even surface.
  • Protect insulation courses from damage using boards if left exposed.
  • Avoid mortar penetration or fracturing of the insulation layer.

• Integration (8.10.1):

  • In-situ concrete withes must be cast integrally with external walls to maintain continuity.

• Protection Against Damp (5.4):

  • Follow proper detailing to prevent moisture ingress through walls.

• Materials (4.1):

  • Use materials conforming to relevant IS codes for brickwork, stone masonry, or concrete block masonry.
  • Damp-proof courses (DPC) and flashings must comply with these standards.

Typical DPC Material Specifications:

General DPC Installation Tips:

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

flowchart TD
    A[Prepare Mortar Bed] --> B[Lay Damp-proof Course]
    B --> C[Protect with Boards if Exposed]
    C --> D[Place Wall Masonry on DPC]
    D --> E[Cast Concrete Withes Integrally]

This ensures effective damp and sound insulation as per IS 1649.

IS 1649: Work at the Top of Flues and Chimneys – Key Points

1. Planning & Design Information (Clause 3.1)

Before work begins, provide detailed info on:

• Locality & exposure of site and chimneys
• Nearby trees and tall buildings
• Prevailing wind directions
• Position of doors/windows relative to fireplaces
• Future appliance changes
• Manufacturer details:
  • Fixing & setting requirements
  • Flue size
  • Chimney height
  • Insulation
  • Air inlets & baffles

2. Size and Height of Flues (Appendix A)

• Flue size and chimney height depend on appliance type.
• Proper sizing ensures safe conduction of combustion products.
• Minimum cross-sectional area and height are specified for efficient draft.

3. General Specifications

• Flues must ensure fire safety, structural strength, thermal insulation, and waterproofing.
• Prevent condensation by proper design and materials.

Typical Flue Sizing Formula (for draft calculation):

[ Q = A \times V ]

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

Example Table: Flue Size for Domestic Appliances (Indicative)

Refer IS 1649 Appendix A for detailed tables.

flowchart TD
    A[Appliance] --> B[Manufacturer Specs]
    B --> C[Flue Size]
    B --> D[Chimney Height]
    B --> E[Insulation & Air Inlets]
    C & D & E --> F[Chimney Design]
    F --> G[Safe Draft & Combustion]

Summary: IS 1649 emphasizes detailed site and appliance data, correct flue

IS 1649: Maintenance and Sweeping of Chimneys

Key Specifications (Clauses 5.23.5 & 5.18)

• Access Openings:

  • Provided at the base and at all bends for flue brush insertion.
  • Size sufficient for cleaning tools.
  • Airtight doors fitted to prevent leakage.
  • Positioned to allow full length sweeping of the flue.

• Soot Doors:

  • Mandatory for cleaning access (Clause 5.18).
  • Must be airtight and easily operable.

Testing for Operation (Clause 12.4)

• Burn old gunny bags or paper in the hearth.
• Smoke should rise freely without obstruction under normal weather.

Design Inputs for Maintenance Planning (Clause 3.1)

• Locality exposure, nearby trees/buildings, prevailing wind direction.
• Position of doors/windows relative to fireplaces.
• Future appliance changes and manufacturer specs:
  • Flue size, chimney height, insulation, air inlets, baffles.

Summary Table: Maintenance Features

flowchart LR
    A[Chimney Design] --> B[Provision of Access Openings]
    B --> C[Soot Doors at Base & Bends]
    C --> D[Full Flue Sweeping Possible]
    A --> E[Testing Operation]
    E --> F[Burn Paper Test]
    F --> G[Smoke Flow Check]
    A --> H[Design Inputs]
    H --> I[Locality & Wind]
    H --> J[Appliance Specs]

Ensure all access openings are airtight and well-placed for effective maintenance and safe operation.

IS 1649: Safety Measures - Fire Protection & Flue Specifications

Key References:

• Fire Safety: IS 1645-1960 (Code of Practice for Fire Safety of Buildings - Chimneys, Flues, Flue Pipes, Hearths)
• Clause 5.2 & 5.11.1: Fire protection and fire safety measures must comply with IS 1645.
• Appendix A (Clauses 1.2 & 5.8.5): Specifies size and height of flues for specific appliances.

Important Specifications:

Note: Actual dimensions depend on appliance capacity and fuel type.

Fire Safety Measures Summary:

• Maintain minimum clearance between flues and combustible materials as per IS 1645.
• Use non-combustible materials for flue construction.
• Ensure proper ventilation to avoid accumulation of flue gases.
• Regular inspection and maintenance to prevent blockages and fire hazards.

flowchart LR
    A[Appliance] --> B[Flue Size & Height per IS 1649 Appendix A]
    B --> C[Fire Safety Compliance per IS 1645]
    C --> D[Clearance & Material Specifications]
    D --> E[Inspection & Maintenance]

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

IS 1649: Domestic Appliances Covered – Key Points

1. Domestic Appliances Scope (Clause 1.2 & Appendix A)

• Appliances covered are listed in Appendix A.
• Flue and chimney construction applies only if appliance heat range is within limits in Appendix A-2 and A-3.

2. Flue Size & Height (Clause 5.8.3 & 5.8.5)

• For appliances > 10,000 kcal/h, flue height must be designed for adequate draught.
• Flue internal dimensions must follow Appendix A specifications.

Typical Flue Design Parameters (from Appendix A)

Draught Design Formula (General)

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

• (D) = draught pressure (Pa)
• (C) = discharge coefficient (~0.65)
• (g) = acceleration due to gravity (9.81 m/s²)
• (H) = chimney height (m)
• (T_i), (T_o) = absolute temperatures inside and outside chimney (K)

flowchart TD
    A[Domestic Appliance] --> B[Heat Output Check]
    B -->|≤10,000 kcal/h| C[Standard Flue Size & Height]
    B -->|>10,000 kcal/h| D[Custom Flue Design]
    D --> E[Calculate Draught]
    E --> F[Determine Flue Height]

Summary: Use Appendix A for appliance list and flue sizes. For >10,000 kcal/h, design flue height based on draught calculations to ensure safe, efficient operation.

IS 1649: Specification for Clay Flue Linings (Appendix B, Clause 4.4)

Key Specifications:

• Minimum wall thickness: ≥ 2 cm
• Straight units length: 30 to 40 cm
• Curved units: Angles between ends either 22½° or 37½° (See Fig. 4D)
• Maximum deviation from straightness: ≤ 6 mm (checked with a straight edge, Fig. 5)
• Maximum deviation from 90° angle between edges: ≤ 6 mm (Fig. 7)
• Maximum deviation from angle between walls: ≤ 6 mm at any point (Fig. 6)

Material Requirements:

• Made from fireclay or terra cotta
• Sound, free from visible defects
• Should give a clear ringing sound when struck with a light hammer (≤ 0.15 kg)
• May be vitrified or glazed/un-glazed

Typical Shapes (Fig. 4):

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

Summary Table:

flowchart TD
    A[Clay Flue Linings] --> B[Material: Fireclay or Terra Cotta]
    A --> C[Wall Thickness ≥ 2 cm]
    A --> D[Straight Units: 30-40 cm]
    A --> E[Curved Units: 22½° or 37½° angles]
    A --> F[Max deviation ≤ 6 mm]
    F --> F1[From straightness]

IS 1649: Chimney Pot Specifications - Key Points

Material & Quality (Clause 1.1)

• Made from fireclay or terra cotta.
• Must be sound, defect-free, and emit a clear ringing when lightly tapped (hammer ≤ 0.15 kg).
• May be vitrified or non-vitrified, glazed or unglazed.

Dimensional Tolerances

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

Shape & Size (Clause 2.1)

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

Base Requirements (Clause 3.1)

• Base must be flat, free from indentations/projections.
• Base must be perpendicular to pot 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 = Flue Lining Section]
    C --> D
    D --> E[Top Diameter = 15 cm (for tapered)]

This ensures chimney pots fit precisely with flue linings and maintain structural integrity per IS 1649.