How to Install a Tankless Water Heater

Installing a tankless water heater involves shutting off utilities, removing the old unit, upgrading gas lines and electrical connections as needed, mounting the new unit, and connecting water and gas lines with proper venting.

1. Kill the Power First. Shut off the main water supply and turn off gas at the meter or electrical power at the breaker. Open hot water faucets throughout the house to drain the existing system. If replacing a tank water heater, disconnect and drain it completely.
2. Clear the Old System. Disconnect gas lines, water lines, and venting from your old unit. For tank heaters, you'll need help moving the heavy unit out. Clear the installation area and check that the new location meets manufacturer clearance requirements from walls and combustibles.
3. Size for the New Load. Most tankless units require larger gas lines than tank heaters. Install new gas line sizing per manufacturer specs, typically 3/4 inch or larger. Run new electrical circuit if needed - many units require 120V power for ignition and controls. Install new electrical outlet near the unit location.
4. Mount Rock Solid. Mount the bracket securely to wall studs using lag bolts. The unit must be level and properly supported. Hang the tankless heater on the mounting system, ensuring it's secure and won't shift during operation.
5. Seal Every Joint. Install shut-off valves on both hot and cold water lines near the unit. Connect water lines to the heater using appropriate fittings. Install pressure relief valve and drain line as required. Consider installing water softener connections if you have hard water.
6. Vent to the Outside. Connect the gas supply line using proper fittings and pipe dope or thread sealant. Install the venting system according to manufacturer specifications - this usually requires new larger diameter vent pipe routed directly outside. Test all gas connections with soapy water for leaks.
7. Verify It All Works. Turn on water and gas supplies slowly. Follow manufacturer startup procedures to initialize the unit. Test all hot water fixtures to ensure proper operation and temperature. Check for any leaks in water or gas connections. Program temperature and flow settings as desired.