How to Install a Tankless Water Heater

Installing a tankless water heater is more involved than replacing a tank heater, but achievable for a confident DIYer. This guide covers both electric and gas units.

Note: Gas line work and electrical panel upgrades must be done by licensed professionals in most areas. Always check local codes first.

Before You Start

Electric tankless: Requires 240V and 150-200 amp service. May need a panel upgrade - consult an electrician first.

Gas tankless: Requires adequate gas pressure, BTU capacity, and proper exterior venting.

What You Will Need

Tankless unit, pipe wrench, drill, PTFE tape, flexible supply lines, voltage tester.

Rheem 18kW Tankless Electric Water Heater - compact and efficient for whole-home electric installation.

Ranein Natural Gas Tankless Water Heater - 8.5 GPM, 190,000 BTU for whole-home gas installation.

Mr. Pen 10-Inch Pipe Wrench - for connecting water supply lines.

Gasoila Yellow PTFE Thread Seal Tape - for all pipe thread connections.

Step 1: Remove the Old Water Heater

Turn off power or gas, shut off cold water supply, drain the tank with a garden hose, disconnect all connections, and remove the unit.

Flexzilla Garden Hose 50ft - for draining the old tank.

Step 2: Choose Location and Mount the Unit

Choose a wall location close to main hot water use areas with access to water lines and gas or electrical connections. Mark anchor points, drill, insert wall anchors, secure the bracket, and hang the unit.

Step 3: Connect the Water Lines

Wrap all threads with PTFE tape. Connect cold water inlet and hot water outlet lines. Install isolation valves on both lines. Tighten all connections firmly with a pipe wrench.

Step 4: Connect Gas or Electricity

Electric: Turn off main breaker. Run correct gauge wire from panel to unit. Connect to terminal block per wiring diagram. Install dedicated breaker. Call a licensed electrician if unsure.

Gas: Connect gas supply line with PTFE tape. Install shutoff valve. Check all connections for leaks with soapy water. Install venting through exterior wall per manufacturer instructions. Call a licensed gas technician for gas line work.

Step 5: Turn On and Test

Turn on cold water supply and check for leaks. Open a hot water faucet to purge air. Restore power or gas. Set temperature to 120 degrees F. Run hot water at several fixtures to confirm proper heating.

Step 6: Plan Annual Maintenance

Descale your tankless heater annually to remove mineral buildup from the heat exchanger.

Tankless Water Heater Flushing Kit - pump, hoses, adapters, and bucket for annual descaling.

When to Call a Professional

• Gas line connections or modifications
• Electrical panel upgrades or new circuits
• Venting through walls or roof
• Any work required by local permit

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