You can have the best of both worlds by installing a hybrid gas water heater. These systems combine features of tank-type and tankless water heaters to improve your home’s energy efficiency and hot water supply. They’re also quieter and take up less space than traditional water heaters.
This guide walks you through the steps to install a hybrid gas water heater, from setup to final testing. Plus, Ask This Old House plumbing and heating expert Richard Trethewey shares the installation process and highlights the hybrid gas water heater system’s benefits in the video segment above.
How Hybrid Gas Water Heaters Work
Hybrid gas water heaters use a heat exchanger and modulating burner to heat water on demand, just like tankless water heaters do. But they also have a small built-in tank—usually holding around 2 gallons—which speeds up your hot water delivery.
Benefits of Hybrid Gas Water Heaters
Hybrid models shine in larger homes where tankless systems might struggle to meet high demand. These heaters can deliver up to 5.5–6 gallons per minute, so you can run multiple showers or taps at once.
Here are a few key advantages of these hybrid models:
- Adjustable output for different demands
- Higher flow rates than tankless models
- Greater energy efficiency
- Quieter operation than traditional tanks
- Reduced standby heat loss
Preparing for Hybrid Gas Water Heater Installation
Ready to install your new hybrid gas water heater? Start by removing the old water heater and gathering the tools you’ll need for a smooth installation.
Removing the old water heater requires some plumbing skills, so you’ll need some do-it-yourself (DIY) plumbing and electrical experience to remove the old model. Here are the instructions to follow:
- Drain the old water heater using a pump.
- Disconnect the cold and hot water connections.
- Remove the gas line and unplug any electrical connections.
- Detach the vent pipe.
- Remove the old unit from its location.
Materials and Tools Needed
Having everything on hand before you start makes the job easier. Gather these items:
- Basic plumbing tools (pipe wrenches, adjustable wrenches, etc.)
- Condensate neutralizer and pump
- Gas line fittings and pipe
- Hybrid gas water heater unit
- Plywood panel for mounting
- PVC pipes for venting and fresh air intake
- Recirculation pump (for larger homes)
- Safety equipment (gloves, safety glasses)
- Temperature and pressure relief valve
- Water supply lines and fittings
Hybrid Gas Water Heater Installation Process
Installing a hybrid gas water heater involves several steps. Unless you’re very experienced in DIY plumbing, we recommend hiring a plumber familiar with local codes. Here’s a general overview of the installation process.
Mounting the Unit
Drain and remove the old water heater. Then, install a plywood panel on the wall where you’ll mount the unit. Attach the hybrid water heater to the panel, and make sure the unit is level and supported.
Connecting the Venting System
Connecting the exhaust vent to the existing vent pipe keeps your home safe by directing combustion gases outside. You’ll also need a fresh air intake pipe to supply air to the burner.
Connect the heater’s exhaust vent to the old vent pipe. Run a fresh air intake line down into the top of the water heater using a PVC pipe. Make sure all connections are sealed and secure.
Water Connections
Your system will need to have the right water connections to operate correctly. To make sure that happens, connect the cold water supply line to the designated inlet and attach the hot water outlet to your home’s hot water distribution system.
Gas Line Installation
You must follow the local codes and regulations when you’re installing the gas line. Your plumber might have to upsize the gas line to accommodate the hybrid water heater’s requirements. Here’s how to install the gas line:
- Run a new gas line to the water heater.
- Install a temperature and pressure relief valve with a discharge pipe.
- Install a shutoff valve near the unit.
- Test the connections for leaks.
Condensate Management
Hybrid gas water heaters produce condensate, which is the liquid phase of condensation. Any time you have a high-efficiency device, condensate is a byproduct. If you allow this water to remain, it could damage the system. Trethewey attaches a condensate line with limestone as a neutralizer and a condensate pump to the underside of the heater to manage the condensate.
Recirculation System (Optional)
Recirculation systems are useful in larger homes because they keep hot water readily available at fixtures that are far from the water heater. Installing a recirculation pump with a timer and sensor will help you optimize energy efficiency. Here’s what to do:
- Install the recirculation pump on the hot water line.
- Connect the return line from the farthest fixture.
- Set up the timer and sensor.
Final Hybrid Gas Water Heater Installation Steps and Activation
Once you’ve made all the connections, it’s time to activate your new hybrid gas water heater.
Perform a final connections check before you turn on the unit by:
- Verifying all water connections are tight.
- Making sure the gas connections are secure and leak-free.
- Confirming that venting and air intake are correctly installed.
- Checking that the condensate system is correctly set up.
Next, turn on the power to the unit and set the water temperature. Plumbers usually recommend setting the temperature to 120 degrees Fahrenheit. Wait for the burner to ignite and begin heating water.
Then, run hot water at various fixtures to check the temperature and flow. Listen for any unusual noises during use. Finally, verify that the recirculation system (if you have one) is working.