Tankless Water Heater Installation Guide

    Professional tips and step-by-step guidance for successful installation

    Important Safety Notice

    Gas and electrical work requires professional installation. Many manufacturers require professional installation to maintain warranty coverage. Always check local codes and obtain necessary permits. Read our buying guide for more information on selecting the right unit.

    1Pre-Installation Planning

    Site Assessment
    • Measure available wall space (minimum clearances)
    • Check existing gas/electrical connections
    • Plan venting route (gas units)
    • Verify water pressure (min 30 PSI)
    Required Tools & Materials
    Basic Tools:
    • • Pipe wrenches and adjustable wrenches
    • • Drill and appropriate bits
    • • Level and measuring tape
    • • Pipe cutting tools
    Materials:
    • • Flexible water connections
    • • Gas flex connector (gas units)
    • • Venting materials
    • • Mounting brackets

    2Electric Unit Installation

    Electrical Requirements
    Typical Requirements:
    • • Small units (11-14kW): 1×60A breaker
    • • Medium units (18-24kW): 2×40A breakers
    • • Large units (27-29kW): 2×60A breakers
    • • Wire gauge: 6 AWG minimum
    Installation Steps:
    1. 1. Turn off main electrical panel
    2. 2. Install dedicated breakers
    3. 3. Run proper gauge wire
    4. 4. Connect to unit terminals
    5. 5. Test all connections

    Electrical Safety Warning

    High-voltage electrical work should only be performed by licensed electricians. Improper installation can cause fires, electrocution, or void warranties. Always obtain electrical permits.

    3Gas Unit Installation

    Indoor Gas Units
    Gas Line Requirements:
    • • ½" or ¾" gas line (check BTU requirements)
    • • Manual gas shutoff valve within 6 feet
    • • Flexible gas connector (CSST approved)
    • • Gas pressure test before connection
    Venting Requirements:
    • • 3" or 4" stainless steel venting
    • • Maximum vent length varies by model
    • • Proper pitch for condensate drainage
    • • Clearance from windows/openings
    Outdoor Gas Units
    Advantages:
    • • No venting required
    • • Simpler installation
    • • More mounting locations
    • • Built-in freeze protection
    Considerations:
    • • Weather protection required
    • • Longer water lines may be needed
    • • Must be accessible for maintenance
    • • Clearance from structures

    Gas Safety Critical Points

    • • Gas work must be performed by licensed professionals in most areas
    • • All connections must be tested for leaks using soapy water or gas detector
    • • Proper combustion air supply is critical for safe operation
    • • Venting must be installed per manufacturer specifications

    4Water Line Connections

    Connection Steps:

    1. 1Shut off main water supply
    2. 2Drain existing water heater
    3. 3Install shutoff valves on both inlet/outlet
    4. 4Connect cold water inlet (blue marking)
    5. 5Connect hot water outlet (red marking)
    6. 6Test for leaks and proper pressure

    Important Tips:

    • Use flexible water connectors to reduce vibration
    • Install pressure relief valve as required
    • Consider water softener if you have hard water
    • Install drain pan if required by local codes

    Common Installation Mistakes to Avoid

    Critical Errors
    • Undersized electrical supply:

      Using inadequate breaker size or wire gauge

    • Improper venting:

      Wrong materials or excessive vent length

    • Gas line too small:

      Insufficient gas pressure reduces performance

    Performance Issues
    • Inadequate clearances:

      Can cause overheating or maintenance issues

    • No water pressure testing:

      Low pressure affects unit performance

    • Skipping commissioning:

      Proper startup and testing is essential

    Installation Cost Breakdown

    Electric Units
    Gas Units
    • Basic installation:$1,000-$1,800
    • Venting system:$500-$2,000
    • Gas line work:$200-$500
    • Permits:$100-$300
    • Total Range:$1,800-$4,600
    • Browse gas units →
    Additional Costs
    • Old unit removal:$100-$300
    • Water softener:$800-$2,000
    • Recirculation pump:$300-$600
    • Extended warranty:$100-$400
    • State/utility rebates:Vary by area (federal 25C credit expired Dec 31, 2025)
    • Calculate your savings →

    Professional Installation vs DIY

    When to Go Professional
    • Gas line work (required by law in most areas)
    • High-voltage electrical (240V+)
    • Warranty requirements specify professional install
    • Complex venting requirements
    • Local codes require permits and inspections
    DIY Considerations
    • Small electric units only (under 120V)
    • Point-of-use applications
    • Existing electrical/plumbing connections adequate
    • Local codes allow DIY installation
    • You have necessary skills and tools

    Installation Success Tips

    Before You Start

    • • Get all necessary permits
    • • Read manufacturer instructions completely
    • • Verify utility requirements
    • • Schedule inspections if required

    During Installation

    • • Follow all safety procedures
    • • Double-check all connections
    • • Test each system as you go
    • • Take photos for future reference

    After Installation

    • • Complete startup procedures
    • • Register warranty with manufacturer
    • • Schedule annual maintenance
    • • Keep all documentation