Code of practice for domestic hot water installations

IS 7558 Scope - Key Specifications & Tables

The code covers centralized domestic hot water supply systems, focusing on storage, flow rates, and pipe sizing.

Key Tables & Formulas

1. Rate of Hot Water Flow (Clause 4.4, Table 2)

Use these minimum flow rates for storage-type hot water installations.

2. Expansion/Vent Pipe Length (Clause 7.2.3, Table 7.1)

For composite pipes, use the largest diameter to determine length.

Additional Notes

• The code harmonizes with BSCP 342-1950 for international coordination.
• Definitions and scope are detailed in Clause 2.0.

flowchart LR
    A[Hot Water Storage] --> B[Fixtures]
    B --> C[Bath Tub: 22.5 L/min]
    B --> D[Kitchen Sink: 18 L/min]
    B --> E[Wash Basin: 7 L/min]
    B --> F[Shower: 7 L/min]
    A --> G[Expansion Pipe]
    G --> H{Diameter}
    H -->|≤ 20 mm| I[Length ≤ 12 m]
    H -->|20-25 mm| J[Length ≤ 7.5 m]
    H -->|> 25 mm| K[Length ≤ 3 m]

This summary provides the essential scope-related data from IS 7558 for design and installation.

IS 7558: Key Definitions & Specifications

Clause 2.0: Definitions

• The code defines terms relevant to domestic hot water supply systems to ensure uniform understanding.
• Definitions cover types of fixtures, storage, flow rates, and installation methods.

Clause 4.4 & Table 2: Rate of Hot Water Flow

• Specifies minimum recommended flow rates for various fixtures in liters per minute (L/min):

Notes:

• These flow rates help in sizing pipes and storage tanks for storage-type hot water installations.
• The code aligns with international standards like BSCP 342-1950 for centralized hot water supply.

Practical Use:

• Use these flow rates to calculate peak demand:
  [ Q_{total} = \sum (n_i \times Q_i) ] where ( n_i ) = number of fixtures, ( Q_i ) = flow rate per fixture.

flowchart LR
    A[Fixture Type] --> B[Flow Rate (L/min)]
    B --> C[Bath tub: 22.5]
    B --> D[Kitchen sink: 18]
    B --> E[Wash basin: 7]
    B --> F[Shower (spray): 7]

This aids in designing efficient hot water systems per IS 7558.

IS 7558 - General Requirements Summary

1. Rate of Hot Water Flow (Clause 4.4, Table 2)

2. Expansion/Vent Pipe Length (Clause 7.2.3, Table 7.1)

Note: For composite pipes, use the largest diameter.

3. Material Suitability for Storage Vessels (Clause 4.6.3, Table 3)

• Galvanized mild steel is not recommended if pH ≤ 7.2.
• For pH ≥ 7.3, minimum temporary hardness (mg/l) required:

4. Valve Testing (Clause 9.4)

• All valves normally left open/closed must be tested for proper operation.
• Rusty or scaled valves must be cleaned or replaced.

flowchart TD
    A[Storage Type Installation] --> B[Fixtures]
    B -->|Flow Rate| C[Bath tub: 22.5 L/min]
    B -->|Flow Rate| D[Kitchen sink: 18 L/min]
    B -->|Flow Rate| E[Wash basin: 7 L/min]
    B -->|Flow Rate| F[Shower: 7 L/min]
    G[Expansion Pipe Diameter] --> H[Length Limits]
    H -->|≤20 mm|

IS 7558: Design Considerations for Hot Water Storage Vessels

Key Points from IS 7558:

• Clause 4.5 (Design of Storage Vessel):
  Design must ensure adequate capacity and pressure resistance for the intended application.

• Clause 4.4 (Rate of Flow - Table 2):
  Minimum recommended flow rates for fixtures:

  Fixture	Flow Rate (liters/min)
  Bath tub	22.5
  Kitchen sink	18
  Wash basin	7
  Shower (spray)	7

• Clause 3.4 (Water Quality Consideration):
  Account for scale-forming and corrosive properties of water to select suitable materials and design for durability.

Additional Design Formulas:

• Storage Capacity (V):
  [ V = \sum (Q_i \times t_i) ] Where:

  • (Q_i) = flow rate of each fixture (l/min)
  • (t_i) = usage duration (min)

• Pressure Vessel Design:
  For cylindrical vessels, thickness (t) is calculated by:
  [ t = \frac{P \times D}{2 \times \sigma \times \eta} ] Where:

  • (P) = design pressure
  • (D) = internal diameter
  • (\sigma) = allowable stress of material
  • (\eta) = joint efficiency

Summary:

• Use Table 2 flow rates for sizing.
• Consider water quality for material selection.
• Calculate storage volume based on fixture demand.
• Design vessel thickness per pressure requirements.

flowchart TD
    A[Identify Fixtures & Flow Rates] --> B[Calculate Total Flow Demand]
    B --> C[Determine Usage Duration]
    C --> D[Compute Storage Capacity V]
    D --> E[Select Material Considering Water Quality]
    E --> F[Calculate Vessel Thickness t]
    F --> G[Design Storage Vessel]

IS 7558: Hot Water Heaters - Key Specifications

1. Types & Rated Capacities (Clause 1.0)

• For dual heaters, input rating = sum of both elements.

2. Insulation Requirements (Clause 4.9.2)

• External surface + handhole cover insulated with ≥ 75 mm thickness of thermal insulation.
• Thermal conductivity ≤ 0.043 K Cal/m²/h/°C/mm.

3. Rate of Hot Water Flow (Clause 4.4, Table 2)

4. Design Considerations (Clause 4.3)

• Storage capacity (max cold water volume)
• Draw-off frequency (rate of utilization)
• Recovery period allowed
• Inlet water temperature

Summary Formula for Storage Capacity Estimation:

[ V = \frac{Q \times t}{\Delta T} ]

Where:

• (V) = Storage volume (litres)
• (Q) = Heat input (kW)
• (t) = Recovery time (hours)
• (\Delta T) = Temperature rise (°C)

flowchart TD
    A[Cold Water Inlet] --> B[Storage Vessel]
    B --> C[Heating Element]
    C --> D[Hot Water Outlet]
    B -. Insulation 75mm .-> E[Thermal Insulation]

This summarizes IS 7558's key points on hot water heaters.

Cold Water Supply to Heaters (IS 7558 Key Points):

1. Storage Tank Capacity (Clause 6.2.1)

• Capacity of cold water storage tank ≥ 2 × capacity of hot water heater.
• If >10 heaters share one tank, capacity ≥ 1.5 × capacity of hot water heater.

2. Separate Tank for Cold Water Supply (Clause 6.2.2)

• Preferably, use a separate cold water tank for hot water heaters.
• If common tank is used, 50% of net capacity must be reserved for hot water heaters.

3. Flow Rates for Fixtures (Clause 4.4, Table 2)

4. Ventilation for Gas Water Heaters (Clause 5.2.11)

• Flue required for prolonged use or poor ventilation.
• Fresh air inlet area ≥ flue socket area.
• Ensure combustion products discharge outside.

Summary Diagram:

flowchart LR
    ColdWaterTank[Cold Water Storage Tank]
    HotWaterHeater[Hot Water Heater]
    Fixtures[Fixtures: Bath, Sink, Basin, Shower]

    ColdWaterTank -->|≥ 2× heater capacity| HotWaterHeater
    HotWaterHeater --> Fixtures
    subgraph FlowRates
        BathTub(Bath tub: 22.5 L/min)
        KitchenSink(Kitchen sink: 18 L/min)
        WashBasin(Wash basin: 7 L/min)
        Shower(Shower: 7 L/min)
    end
    Fixtures --> FlowRates

Use these specs to ensure adequate cold water supply and safe operation of heaters per IS 7558.

IS 7558: Hot Water Delivery & Ventilation Key Points

1. Rate of Hot Water Flow (Clause 4.4, Table 2)

2. Vent Pipe Specifications (Clause 7.1.1)

• Minimum bore: 20 mm

• Height above cold water tank water line:

  [ \text{Vent height} = 15,cm + \left(\frac{1,cm}{30,cm} \times \text{height of water line above heater bottom}\right) ]

• Vent must discharge above cold water tank level.

• Ensure vent discharge does not cause scalding or injury.

3. Installation Schemes (Clauses 6.2.5 & Figures 3-5)

• For multi-storeyed buildings, overhead tanks can be common or individual per shaft/floor group.
• Individual storage tanks per flat are allowed as alternate arrangements.
• Hot water heaters are fed from these storage tanks.

Mermaid Diagram: Vent Pipe Height Calculation

flowchart TD
    A[Bottom of Heater] --> B[Water Line Height (h)]
    B --> C[Calculate Vent Height]
    C --> D[Vent Height = 15 cm + (h/30) cm]
    D --> E[Vent Pipe rises above Water Line]

Summary: Use Table 2 for flow rates, ensure vent pipes ≥20 mm bore with correct height, and follow installation layouts per building height/type.

IS 7558: Thermal Insulation Key Points

Clause 4.9 - Thermal Insulation

• 4.9.1: Insulate hot water storage vessels and pipes to minimize heat loss for efficiency and economy.
• 4.9.2: Entire external surface of the storage vessel, including handhole covers, must have thermal insulation equivalent to:
  • Minimum thickness: 75 mm
  • Thermal conductivity: ≤ 0.043 Kcal/m²/h/°C/mm

Summary Table: Thermal Insulation Specification

Additional Notes:

• Proper insulation reduces heat loss, maintaining water temperature and saving energy.
• Use materials like mineral wool, glass wool, or foam with the specified conductivity.
• Thickness can be adjusted if conductivity differs, maintaining equivalent thermal resistance.

Thermal Resistance Formula

[ R = \frac{d}{k} ]

Where:

• (R) = thermal resistance (m²·°C/W)
• (d) = thickness of insulation (m)
• (k) = thermal conductivity (W/m·°C)

flowchart LR
    A[Hot Water Storage Vessel] --> B[Thermal Insulation]
    B --> C{Thickness ≥ 75 mm}
    B --> D{Conductivity ≤ 0.043 Kcal/m²/h/°C/mm}
    C & D --> E[Minimized Heat Loss]
    E --> F[Improved Efficiency & Economy]

This ensures compliance with IS 7558 for thermal insulation on hot water vessels.

IS 7558: Inspection and Maintenance - Key Points & Specifications

Clause 9.7 - Maintenance Records & Inspection:

• Keep record drawings of piping layout and valve positions updated.
• Inspect regularly to ensure no cross-connections or undesirable features post-maintenance.
• Record all additions or alterations promptly.

Clause 9.1 - Regular Inspection:

• Inspect system for leakages and corrosion regularly.

Clause 9.4 - Valve Testing:

• Test valves normally left open/closed by operating them fully.
• Clean or replace valves with rust or scale deposits.

Useful Table from Clause 4.4 (Flow Rates for Hot Water Fixtures)

Maintenance Best Practices Summary

• Update drawings after every maintenance.
• Inspect valves for functionality and cleanliness.
• Check for leaks/corrosion frequently.
• Maintain flow rates as per Table 2 for system performance.

flowchart LR
    A[Maintenance Work] --> B[Update Record Drawings]
    B --> C[Inspect Piping & Valves]
    C --> D{Any Cross-Connections?}
    D -- Yes --> E[Correct Immediately]
    D -- No --> F[Continue Operation]
    C --> G[Check Valves Operation]
    G --> H{Valve Rust/Scale?}
    H -- Yes --> I[Clean or Replace Valve]
    H -- No --> F

This ensures safe, efficient, and code-compliant system operation.

IS 7558 - Electrical Installation Requirements: Key Points

IS 7558 refers to electrical installations with references to:

• IS 4648:1968 — Guide for electrical layout in residential buildings
• IS 732:1963 — Code of practice for electrical wiring (up to 650 V)

Key Specifications:

• Plans & Documentation (Clause 3.5):
  Provide permanent, clear layout plans after installation for record and future reference.

• Earth Continuity Check (Clause 9.3):
  Verify earth continuity of the installation. Correct any defects to ensure safety against electric shock.

Important General Guidelines (from IS 732):

Basic Earth Continuity Test Formula:

[ R_{earth} = \frac{V}{I} ]

Where:

• (V) = voltage drop measured
• (I) = test current applied

flowchart TD
    A[Start Installation] --> B[Plan Electrical Layout]
    B --> C[Install Wiring as per IS 732]
    C --> D[Complete Installation]
    D --> E[Check Earth Continuity]
    E --> F{Earth Continuity OK?}
    F -- Yes --> G[Record Plans & Documentation]
    F -- No --> H[Correct Defects and Recheck]
    H --> E

Summary: Follow IS 732 for wiring practices, ensure earth continuity per IS 7558 Clause 9.3, and maintain proper documentation as per Clause 3.5.

IS 7558: Safety & Regulatory Compliance (Ref: IS 302-1967)

Key Points:

• Valve Testing (Clause 9.4):

  • All valves normally left open/closed must be tested by operating them fully to ensure proper function.
  • Rusty or scaled valves must be cleaned or replaced.

• Maintenance Records (Clause 9.7):

  • Maintain up-to-date drawings of piping layout and valve positions.
  • Inspect regularly to prevent cross-connections or unsafe alterations.
  • Record all system additions or changes promptly.

General Safety Guidelines for Light Electrical Appliances (IS 302-1967)

• Appliances must comply with electrical insulation, earthing, and protection against electric shock.
• Regular inspections and maintenance are mandatory.
• Use only certified components and follow manufacturer instructions.

Summary Table: Valve & Maintenance Compliance

For detailed specifications, contact BIS Regional Offices listed in IS 7558 or visit BIS website.

flowchart TD
    A[Valve Testing] --> B{Valve Condition}
    B -->|Good| C[Record Operation]
    B -->|Rusty/Scaled| D[Clean or Replace Valve]
    C --> E[Update Maintenance Records]
    D --> E
    E --> F[Inspect for Cross-Connections]
    F --> G[Safe System Operation]

Note: IS 7558 relies on IS 302-1967 for electrical appliance safety; always consult both for compliance.