To install a gas tankless water heater, connect the gas line, water supply, and venting system, ensuring proper clearance and following local codes for safety.
Gas tankless water heaters provide endless hot water while saving energy and space. Proper installation is critical for safety and performance. Follow this detailed guide to install your unit correctly.
Pre-Installation Requirements
Before purchasing your tankless water heater, complete these essential steps:
1. Verify Gas Line Capacity
Tankless units require 3-4 times more gas than traditional heaters (90,000-199,000 BTU/hr). Most homes need:
- 1″ gas line for units under 150,000 BTU
- 1.25″ line for larger units
Consult a licensed plumber to upgrade your gas line if needed. Never attempt this yourself.
2. Check Venting Options
Direct-vent models require:
- Stainless steel vent pipes
- Minimum 12″ clearance from windows/doors
- Vertical or horizontal vent runs per manufacturer specs
Consider a built-in gas heater if venting is challenging.
3. Select Location
Choose an area with:
- Access to existing plumbing
- Proper clearances (typically 6″ sides, 12″ front)
- Vent path to exterior
- Near gas supply line
Installation Process
1. Remove Old Water Heater
- Turn off water supply and gas line
- Drain tank completely
- Disconnect all plumbing and gas connections
- Properly dispose of old unit
2. Mount New Unit
Follow manufacturer instructions for:
- Wall mounting height
- Required clearances
- Sturdy mounting surface
Use a reinforced mounting box if installing on drywall.
3. Connect Water Lines
Install with:
- Shutoff valves on both lines
- Dielectric unions to prevent corrosion
- Flexible connectors for vibration isolation
Consider adding a check valve to prevent backflow.
4. Install Gas Line
Key requirements:
- Use black iron or CSST piping
- Install sediment trap
- Apply pipe compound only on male threads
- Pressure test all connections
Always hire a professional for gas line work.
5. Vent Installation
Follow these venting rules:
| Vent Type | Maximum Length | Elbow Limit |
|---|---|---|
| 2″ PVC | 20 feet | 4 elbows |
| 3″ Stainless | 50 feet | 6 elbows |
Seal all joints with high-temperature silicone.
6. Electrical Connection
Most units require:
- 120V outlet nearby
- Dedicated circuit for models with recirculation pumps
- Proper grounding
Startup and Testing
1. Initial System Flush
Before first use:
- Connect hoses to service valves
- Flush unit for 15 minutes
- Check for debris in filter screen
2. Gas Pressure Test
Verify proper gas pressure:
- Natural gas: 7″ water column
- Propane: 11″ water column
3. Check for Leaks
Test all connections with:
- Soap solution for gas lines
- Paper towel for water lines
4. Adjust Temperature
Set to 120°F for optimal efficiency and safety. Higher temperatures increase scaling risk.
Maintenance Tips
Extend your heater’s life with these practices:
Annual Descaling
Use a descaling pump and vinegar solution to remove mineral deposits.
Monthly Filter Cleaning
Clean inlet water filter to maintain flow rate.
Vent Inspection
Check vent termination for obstructions seasonally.
For complex installations, consider professional help. The U.S. Department of Energy provides additional safety guidelines.
