Replacing a tankless water heater involves assessing the current system, choosing the right replacement, and following proper installation, venting, and code requirements. This guide covers when to replace, how to select a unit, steps for removal and installation, safety considerations, and ongoing maintenance. It emphasizes both gas and electric models, sizing, and cost factors to help homeowners make informed decisions.

Why Replace A Tankless Water Heater

Common reasons for replacement include declining efficiency, frequent repairs, outdated venting, or inadequate hot water supply. Modern tankless units offer higher efficiency, better controls, and improved hot water delivery. If a unit is beyond repair or cannot meet household demand, replacement is often the most cost-effective option in the long term.

Choosing The Right Replacement Tankless Water Heater

Key factors influence selection:

Hot water demand: Determine peak gallons per minute (GPM) your household requires. A typical shower uses 1.5–2.0 GPM; multiple fixtures demand higher flow.
Energy source: Decide between gas and electric tankless heaters. Gas models generally offer higher flow at a lower operating cost in many homes, while electric models are easier to install where gas is unavailable.
Efficiency ratings: Look for Energy Factor (EF) or Uniform Plumbing Code (UPC) efficiency values. Higher ratings reduce operating costs.
Ventilation and clearances: Gas units require proper venting and exhaust routing. Electric models require minimal venting but may need electrical upgrades.
Space and installation: Consider mounting options, piping layout, and accessibility for service.
Brand reliability and service: Check warranties, parts availability, and local contractor support.

Preparation And Safety

Before removal, shut off power and fuel, drain the system, and relieve pressure. For gas units, close the gas valve and disconnect gas supply. For electric units, switch off the circuit breaker and disconnect the power supply. Have a drainage plan for hot water and use protective gear. If water lines are corroded or the venting appears damaged, plan for additional costs or professional assistance.

Removal Of The Old Unit

Safe removal steps include:

Turn off all utilities and depressurize the system.
Disconnect water, gas (for gas models), and electrical connections.
Carefully detach mounting hardware and remove the old unit, inspecting connections for corrosion or damage.
Cap or reconfigure refrigerant-free lines if needed (for some heat-exchanger configurations) and prepare the space for the new unit.

Note: If the existing venting configuration is incompatible with the new unit, plan for vent modification by a licensed professional to maintain safety and code compliance.

Installation Considerations

Accurate installation ensures performance and safety. Consider the following:

Sizing: Verify the new unit’s capacity matches household demand. Oversizing wastes energy; undersizing leads to inadequate hot water.
Piping: Use appropriate materials and correct pipe sizing to minimize pressure drop. Include isolation valves for easier future maintenance.
Ventilation: Gas models require vertical or horizontal venting with appropriate material and slope. Ensure proper clearance from combustibles per code.
Gas supply and pressure: Confirm supply line size and regulator ratings. Inadequate gas pressure can impair performance.
Electrical requirements: Electric models may require dedicated circuits and correct amperage. Check panel capacity and future load calculations.
Drain and condensate management: Install appropriate drainage for condensate and relief devices to prevent water damage.
Seismic and warranty considerations: Secure mounting and follow manufacturer instructions to preserve warranty coverage.

Follow the manufacturer’s installation manual precisely and adhere to local codes. If in doubt, hiring a licensed plumber or HVAC technician is advisable to ensure compliance and safety.

Commissioning And Testing

After installation, perform a step-by-step verification:

Restore power and fuel supply, then prime the system and check for leaks.
Bleed air from lines and verify hot water temperature at multiple fixtures.
Test the unit’s safety features, such as flame sensors, pressure relief, and anti-scald controls.
Inspect venting integrity for gas models, ensuring there are no obstructions or leaks.
Review thermostat settings and ensure reasonable water temperatures to avoid scalding.

Record installation details, serial numbers, and warranty information for future service needs.

Costs, Permits, And Warranties

Costs vary by unit type, complexity, and labor. Typical ranges include equipment cost, installation labor, and potential electrical or gas upgrades. Permit requirements depend on local codes and whether venting or gas line work is involved. Many installers include permit handling. Warranties commonly cover parts for 5–12 years and labor for 1–2 years, though terms vary by brand and region. Retain proof of purchase and installation documentation for warranty claims.

Maintenance After Replacement

To maximize efficiency and lifespan, schedule regular maintenance:

Flush the unit annually to remove mineral buildup and sediment.
Inspect and replace anode rods or sensors as recommended by the manufacturer.
Test pressure relief devices and check venting for blockages or corrosion.
Monitor energy usage and performance to catch early signs of decline.

Energy savings can improve with temperature setpoints aligned to household needs, regular maintenance, and prompt repairs of leaks or inefficient components.

Professional Vs. DIY Considerations

Replacing a tankless water heater involves complex electrical, gas, and venting work. DIY installation may void warranties or create safety risks. A licensed plumber or HVAC contractor can ensure code compliance, proper venting, and safe gas connections. Homeowners should weigh upfront savings against long-term risk and potential code penalties.