Type L Copper Piping for Domestic Hot Water Systems

Overview

Type L copper tubing represents the medium-wall thickness standard for domestic hot water (DHW) distribution systems, offering superior pressure capacity and durability compared to Type M copper. Manufactured to ASTM B88 specifications, Type L copper is the preferred choice for underground installations, higher-pressure applications, and environments requiring enhanced corrosion resistance.

The primary distinguishing characteristic of Type L copper is its wall thickness, which ranges from 0.045 inches (1.14 mm) for 1/2-inch nominal diameter up to 0.070 inches (1.78 mm) for larger sizes. This increased material thickness provides:

• Enhanced pressure rating capability
• Superior mechanical strength for underground burial
• Improved resistance to water hammer and pressure transients
• Extended service life in aggressive water conditions
• Better resistance to physical damage during installation

Wall Thickness and Pressure Ratings

The wall thickness for Type L copper tubing is defined by ASTM B88 and varies with nominal pipe size. The relationship between internal pressure rating and wall thickness follows the Barlow formula:

$$P = \frac{2 \cdot S \cdot t}{D}$$

Where:

• $P$ = allowable internal pressure (psi)
• $S$ = allowable stress for copper (typically 6,000 psi for annealed, 10,000 psi for drawn temper)
• $t$ = wall thickness (inches)
• $D$ = outside diameter (inches)

For Type L copper, typical working pressure ratings at ambient temperature are:

At elevated DHW temperatures (140°F), pressure ratings decrease by approximately 20% due to thermal degradation of material strength.

Type L vs Type M Applications

The selection between Type L and Type M copper depends on installation conditions, local code requirements, and system operating parameters:

Underground Service Applications

Type L copper is the standard specification for underground water service for several critical reasons:

Soil Conditions: Underground piping experiences soil loading, potential settlement, and backfill compaction forces. The heavier wall thickness of Type L provides necessary resistance to crushing and deformation.

Corrosion Environment: Soil chemistry varies significantly. Type L’s additional material provides a corrosion allowance, ensuring adequate remaining wall thickness even after localized corrosion occurs.

Code Requirements: The International Plumbing Code (IPC) Section 605.4 and Uniform Plumbing Code (UPC) Section 604.1 typically mandate Type L for underground installations. Type M is explicitly prohibited underground in most jurisdictions.

Installation Protection: Type L must be installed with:

• Minimum 12-inch burial depth below frost line
• Sand bedding and backfill (no sharp rocks or debris)
• Continuous support (no point loads or spanning)
• Proper identification tape located 6-12 inches above pipe

Joining Methods

Type L copper for DHW systems utilizes several approved joining methods:

Soldered Joints (ASTM B828):

• 95-5 tin-antimony solder for potable water (lead-free)
• Joint temperature: 350-450°F
• Flux residue must be water-soluble and non-corrosive
• Provides tensile strength: 2,500-3,000 psi

Brazed Joints (AWS A5.8):

• BCuP series phosphor-copper alloys (typically BCuP-3 or BCuP-5)
• Joint temperature: 1,300-1,500°F
• No flux required for copper-to-copper joints
• Provides tensile strength: 25,000-40,000 psi
• Required for medical gas and critical systems

Mechanical Joints:

• Press-fit systems (Viega ProPress, Ridgid MegaPress)
• Compression fittings for smaller diameters (≤2")
• Grooved mechanical couplings for larger sizes

Type L Sizing Chart

The following diagram illustrates the relationship between Type L copper sizing, flow velocity, and pressure drop considerations:

graph TD
    A[Type L Copper Sizing] --> B[Flow Rate Demand GPM]
    B --> C{Velocity Check}
    C -->|< 5 fps| D[Acceptable - Quiet Operation]
    C -->|5-8 fps| E[Acceptable - Normal Residential]
    C -->|> 8 fps| F[Reduce Size - Erosion Risk]

    B --> G[Pressure Drop Calculation]
    G --> H{Δp per 100 ft}
    H -->|< 4 psi| I[Excellent Sizing]
    H -->|4-8 psi| J[Acceptable Sizing]
    H -->|> 8 psi| K[Increase Size]

    D --> L[1/2 inch: Up to 4 GPM]
    E --> M[3/4 inch: 4-10 GPM]
    E --> N[1 inch: 10-20 GPM]
    J --> O[1-1/4 inch: 20-30 GPM]
    J --> P[1-1/2 inch: 30-45 GPM]
    I --> Q[2 inch: 45-75 GPM]

    style F fill:#ff6b6b
    style K fill:#ff6b6b
    style I fill:#51cf66
    style D fill:#51cf66

Material Properties and Corrosion Resistance

Type L copper exhibits excellent corrosion resistance in most potable water conditions. The material composition per ASTM B88 requires:

• Copper content: 99.9% minimum
• Phosphorus: 0.015-0.040% (deoxidized grade)
• Thermal conductivity: 226 BTU/(hr·ft·°F) at 68°F
• Coefficient of thermal expansion: $9.8 \times 10^{-6}$ per °F

The phosphorus content provides deoxidation, preventing hydrogen embrittlement and improving resistance to oxygen corrosion in water service.

Water Chemistry Considerations:

Corrosion rate depends on water characteristics:

$$\text{Corrosion Rate} \propto \frac{[\text{Dissolved Oxygen}] \cdot [\text{Chlorides}]}{\text{pH} \cdot [\text{Alkalinity}]}$$

Type L performs well in:

• pH range: 6.5-8.5
• Total dissolved solids: <500 mg/L
• Chloride content: <250 mg/L
• Sulfate content: <250 mg/L

Waters outside these parameters may require water treatment or alternative piping materials.

Installation and Service Life

Proper installation practices maximize Type L copper service life:

1. Storage and Handling: Protect tubing ends with plastic caps. Store on racks above ground. Avoid contamination.

2. Cutting: Use tubing cutters (not hacksaws). Ream all burrs completely.

3. Cleaning: Clean and flux within 4 hours of cutting. Use appropriate flux for solder type.

4. Support Spacing:

   • Horizontal runs: 6 feet for 1" and smaller, 8 feet for 1-1/4" and larger
   • Vertical runs: 10 feet maximum spacing

5. Expansion Allowance: Provide for thermal expansion at $9.8 \times 10^{-6}$ in/in/°F. A 100-foot run experiences 1.4-inch expansion from 40°F to 180°F.

Expected service life for properly installed Type L copper in DHW applications exceeds 50 years in normal water conditions, with many installations performing reliably for 75+ years.

Code Compliance

Type L copper installations must comply with:

• ASTM B88: Standard specification for seamless copper water tube
• IPC Section 605: Materials for water distribution
• UPC Section 604: Materials and joints for water piping
• NSF/ANSI 61: Drinking water system components
• Local amendments: Always verify local code requirements

Type L copper is universally accepted by all model plumbing codes for both above-ground and underground potable water service.