How To Replace a Direct Vent Water Heater

Replacing a direct vent water heater is a complex task that requires experience with plumbing, gas, and electrical hookups. This project requires careful planning and execution to guarantee safety and proper installation.

In the video above, This Old House plumbing and heating expert Richard Trethewey shares his step-by-step process for installing a new direct vent water heater. This guide walks you through each step so you can replace your water heater with confidence.

What Is a Direct Vent Water Heater?

They use a specialized venting system that draws combustion air from outside and expels exhaust gases through the same vent. Because of this, they’re suitable for homes without a traditional chimney. This design also makes them energy efficient and safer than power-vented water heaters, especially in tightly sealed homes.

These heaters generally last between 8 and 12 years, with costs for replacement ranging anywhere from $750–$2,950*, including labor.

*Cost information is based on 2024 data from Angi. 

Advantages of Direct Vent Water Heaters

Direct vent water heaters offer several advantages that make them a preferred option in many homes:

• Energy efficiency: By using outdoor air for combustion and venting exhaust directly outside, these units are highly efficient.
• Safety: By venting directly outdoors, they reduce the risk of exhaust gases re-entering the home.
• Versatility: Ideal for homes without access to a chimney, providing flexible installation options.

Preparing for Water Heater Installation

Pro Tip: Richard Trethewey, This Old House plumbing and heating expert, has a simple rule for any job like this: “The cardinal rule before starting any plumbing project: Turn off the water.”

Before you start, gather all the necessary tools and materials for a smooth installation process.

Required Tools and Materials

• Pliers
• Propane torch
• PVC pipes and fittings
• PVC pipe cutter
• Silicone sealant
• Solenoid valve (optional)
• Teflon tape
• Tubing cutter
• Water transfer pump and hose
• New direct vent water heater

Safety Precautions

When working with gas appliances, safety should be your top priority. Always follow these guidelines:

• Make sure the workspace is well-ventilated.
• Keep a fire extinguisher nearby.
• Turn off the gas supply before starting any work.
• Wear protective gear, including gloves and safety glasses.
• If you’re unsure about any step, stop and consult a professional plumber.

Safety Note: As Richard Trethewey explained on This Old House, many water heaters are in basements or garages where people store gasoline for lawn mowers or keep paint. He warns: “Had you spilled any of those liquids, the fumes could be drawn right into here. And the gas pilot could cause a fire, thousands of fires every year. There’s even deaths, many deaths every year.” These risks led to updated safety standards for water heaters in 2003.

Pro Tip: Richard Trethewey, This Old House plumbing and heating expert, advises that in garages, gas-fired water heaters should be positioned 18 inches above the floor to keep from igniting gasoline fumes, which are heavier than air. He also recommends labeling the shut-off valve on the cold-water supply for quick shutdowns and piping the end of the relief valve to a drain or an area that can safely handle pressurized steam or scalding-hot water.

Removing the Old Water Heater

Start by safely disconnecting and removing the old water heater to prepare the space for the new unit.

Disconnecting Utilities

Close the cold water supply valve and shut off the gas supply to the existing water heater. Unplug the water heater from any electrical outlets.

Draining the Tank

Pro Tip: Before draining, always turn off the electrical disconnect or gas supply to the water heater first. As Richard, This Old House plumbing and heating expert, explains on a project: “Turn off the electrical disconnect coming into the water heater, and that’s obviously for safety. And also we don’t want to ever run these electrical heating elements without water behind them or the elements will burn up.”

Use a hose and electric pump to the drain valve to empty the tank:

1. Attach an electric pump and garden hose to the drain valve near the bottom of the water heater.
2. Extend the hose outdoors, then open the valve and turn on the electric pump to siphon water from the heater’s tank.
3. Open the hot water faucets throughout your house to let air into the system and speed up drainage.
4. Once the water heater tank is empty, turn off the pump and close the house faucets.

Removing Connections

Clean the water pipes to ensure smooth disconnections:

1. Use a strip of emery cloth to clean the hot water copper pipe leading into the water heater.
2. Cut the hot water pipe with a tubing cutter.
3. Repeat Steps 1 and 2 to cut through the cold water pipe.
4. Use two pliers to loosen the union fitting that connects the gas line to the water heater.
5. Carefully carry the old water heater out of the area.

The gas line connection is designed to be separated without cutting. As Richard told homeowner Amy while disconnecting a 50-year-old water heater: “This is called a union and it’s made to come apart.” A union fitting has a central nut that, once loosened with two wrenches, allows the pipes to separate cleanly — no cutting or threading required.

Installing the New Water Heater

With the old unit removed, you’re ready to install the new direct vent water heater.

Preparing the New Unit

Start by attaching the necessary components to the new heater:

1. Wrap Teflon tape around the hot and cold water connections protruding from the top of the new water heater.
2. Thread a vacuum valve onto a brass water heater T-fitting, then thread the T-fitting onto the heater’s cold water connection.
3. Thread a 3/4-inch copper fitting onto the heater’s hot-water connection.
4. Tighten the fittings with pliers.

Connecting the Heater

Set the water heater into position, then follow this process:

1. Solder the hot and cold water pipes to the corresponding connections on the water heater.
2. Reconnect the gas line to the water heater, tightening the connection with pliers.

Installing the Power Vent

The power vent removes exhaust gases while drawing in fresh air for combustion:

1. Attach the power vent to the top of the water heater.
2. Make the necessary electrical connections.
3. Join the exhaust port on the power vent to the existing vent pipe using PVC pipe and fittings.
4. Glue together the parts with PVC primer and cement.

Final Steps and Water Heater Safety Features

After installation, focus on leak prevention, sealing, and testing.

Leak Prevention

To prevent potential water damage, Cook recommends installing a solenoid valve below the cold water shutoff valve. Plug the solenoid’s power cord into an electrical outlet and set its moisture sensor on the floor beside the water heater.

This device automatically shuts off water if it detects a leak, giving you added peace of mind.

Sealing and Testing

With everything connected, apply a continuous bead of silicone sealant around the base of the water heater. Open the gas valve and water supply valves, then plug in the water heater. Run a test to confirm everything is working correctly and check all the connections for leaks.

Additional Considerations

If you’re installing the water heater in a confined space like a basement, you may need to add ventilation or a drain pan for extra protection. Always follow your local building codes and manufacturer guidelines to guarantee a safe installation.

Maintenance and Care of Your New Direct Vent Water Heater

Routine maintenance can extend your heater’s life and keep it running efficiently:

• Flush the tank annually: This clears sediment buildup, helping your heater perform better.
• Inspect the anode rod: Every few years, check this rod to prevent corrosion inside the tank. Inspecting and replacing it when necessary can prolong the life of your heater.
• Check the temperature and pressure relief valves: Regularly test these for functionality and to prevent potential safety hazards.
• Clear the area around the heater: Keep flammable items away from the heater.
• Schedule professional inspections: Have a plumber inspect the unit every few years.