Tankless Geek topic guide

    Tankless Water Heater Gas-Line Sizing

    Gas-line sizing depends on appliance input, fuel, pressure, pipe material, developed length and every connected load.

    Updated

    Direct answer

    Do not choose a gas-pipe diameter from a rule of thumb. A qualified installer must use the adopted fuel-gas code tables, the heater manual and the building's total connected load.

    Inputs that matter

    Record the heater's maximum BTU per hour, gas type, supply pressure, pipe material, developed length, fittings and other appliances served.

    Why undersizing matters

    Insufficient supply can cause ignition problems, reduced output or unsafe operation. A larger heater may require changes upstream of the appliance.

    Authority and manual

    NFPA 54 or another adopted code may apply, with local amendments. Follow the exact manufacturer's installation instructions and local inspection requirements.

    Questions people ask

    Is 3/4 inch gas pipe always enough?

    No. Capacity changes with fuel, pressure, material, length, fittings and other connected appliances.