How to Install a Propane Tankless Water Heater

Upgrading to a propane tankless water heater can significantly improve your home’s energy efficiency and provide an endless supply of hot water. This modern appliance heats water on demand, eliminating the need for a large storage tank and reducing energy waste. In the video above, Richard Trethewey demonstrates the process of replacing a traditional tank water heater with a more efficient tankless model.

Understanding Propane Tankless Water Heaters

Propane tankless water heaters offer several advantages over conventional tank-style units. These compact devices heat water instantly as it flows through the unit, providing hot water only when needed. This on-demand heating system results in significant energy savings and a continuous supply of hot water.

Pro Tip: Richard Trethewey, plumbing and heating consultant for This Old House, points out that a gas-fired tankless system typically knocks about a third off of water-heating bills. The savings occur because tankless heaters only fire up when needed, eliminating the energy waste of keeping a large tank hot around the clock.

The case for going tankless becomes even stronger when you consider the limitations of conventional tanks. As This Old House Magazine has noted, most households fill up 40- to 50-gallon storage tanks and pour energy into them 24/7, year in and year out—only to run out of hot water when a teenager takes a long shower or a spouse settles in for a tub soak. Tanks generally fail in 8 to 12 years, and sediment buildup can rob them of efficiency long before that. A tankless unit generates hot water only when you need it, and for as long as you need it, saving 27 to 50 percent of fuel costs over a tank-style heater.

Benefits of Propane Tankless Water Heaters

Propane tankless water heaters offer numerous advantages for homeowners:

• Energy efficiency: They only heat water when needed, reducing standby energy losses.
• Lower operating costs: Reduced energy consumption leads to lower utility bills over time.
• Endless hot water: Enjoy a continuous supply of hot water without running out.
• Space-saving design: Compact units can be mounted on walls, freeing up valuable floor space.
• Longer lifespan: Tankless units typically last longer than traditional tank water heaters.

How Propane Tankless Water Heaters Work

Propane tankless water heaters operate on a simple principle:

1. When a hot water tap is opened, cold water enters the unit.
2. A flow sensor detects the water movement and activates the heating element.
3. Propane gas ignites, heating the water as it passes through a heat exchanger.
4. The heated water exits the unit and travels to the open faucet.
5. When the tap is closed, the unit shuts off, conserving energy.

Preparing for Propane Tankless Water Heater Installation

Before installing a propane tankless water heater, proper preparation creates a smooth and safe installation process.

Choosing the Right Unit

When selecting your tankless water heater, we recommend doing the following:

• Calculate your home’s peak hot water demand to determine the required flow rate.
• Consider the incoming water temperature in your area to ensure sufficient heating capacity.
• Evaluate the available space for installation and choose a unit that fits comfortably.
• Check local building codes and regulations to ensure compliance.

Expert Insight: This Old House plumbing and heating expert Richard Trethewey cautions that tankless heaters “aren’t for everybody.” In a household with lots of simultaneous water use — say, multiple showers running at the same time as the dishwasher or washing machine — a tankless heater may not be able to keep up with demand. That’s because there’s a limit on how much water can flow through the unit at any one time.

How Pros Size a Tankless Unit: According to This Old House Magazine, a plumber determines whether a heater can meet a household’s needs by looking at three factors: the temperature of the water coming into the heater, the peak demand for hot water in gallons per minute (gpm), and the heater’s efficiency, as indicated by its Uniform Energy Factor found in the product specs. If a heater’s Btu output can’t keep up with demand, it will cut back the flow — or worse, deliver lukewarm water.

Gathering Necessary Tools and Materials

Collect all required tools and materials before beginning the installation:

• Copper pipe and fittings
• Mounting hardware
• Pipe joint compound
• Pipe wrench
• Propane torch
• Threaded iron pipe and fittings
• Teflon tape
• Tubing cutter
• Union fitting
• Ventilation materials (if required)

Safety Precautions

Prioritize safety throughout the installation process:

• Ensure proper ventilation in the work area.
• Have a fire extinguisher readily available.
• Shut off the gas supply at the meter or tank.
• Turn off the main water supply and drain the existing water heater.
• Wear appropriate personal protective equipment, including gloves and safety glasses.

Step-by-Step Installation Process for a Propane Tankless Water Heater

1. Turn off the main water valve at the meter.
2. Cut into the existing water–supply pipes attached to the old water heater.
3. Remove the old water heater and mount the new tankless heater to the wall.
4. Run threaded iron pipe from the outdoor propane tank to the heater; tighten all connections with a pipe wrench.
5. Use a union fitting to connect the threaded gas pipe to the heater.
6. Run copper pipe from the existing water-supply line to the heater. Solder all copper connections.
7. Open the main water valve, and check your work for leaks.
8. Turn on the propane and plug the heater into a nearby electrical outlet.
9. Set water temperature to 120 degrees F at the heater’s control panel.

Water Heater Maintenance and Troubleshooting

Regular maintenance helps keep your propane, tankless water heater operating efficiently and extend its lifespan.

Routine Maintenance Tasks

Routine maintenance keeps your water heater running smoothly and prevents common issues.

• Flush the system annually to remove mineral buildup.
• Inspect and clean the burner assembly periodically.
• Clean or replace the inlet water filter as needed.
• Check and tighten all connections annually.

Common Issues and Solutions

Understanding common issues and their solutions can prevent disruptions.

• Fluctuating water temperature: Clean the inlet filter and check for proper gas pressure.
• No hot water: Check the power supply, gas connection, and water flow.
• Strange noises: Flush the system to remove scale buildup.
• Error codes: Consult the user manual for specific troubleshooting steps.

Our Conclusion

Installing a propane tankless water heater can significantly improve your home’s energy efficiency and provide an endless supply of hot water. While the installation process requires careful planning and execution, the long-term benefits make it a worthwhile investment for many homeowners. For optimal results and safety, consider hiring a professional plumber to handle the installation.

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