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The Tankless Water Heater Installation Process

NexGen The Tankless Water Heater Installation Process

It’s best to leave tankless water heater installation to a professional. The process is too complex for a DIYer. While tankless units are smaller and more straightforward than traditional tank-based water heaters, they require precise connections. Any mistakes can reduce efficiency and put your safety at risk. 

NexGen specializes in water heater repair and installation. If you’ve never had a tankless water heater installed, here’s a look at how the installation process works:


Plumbing, gas, electrical, and vent work may be required before disconnecting your old water heater. Assuming you’re installing a gas unit, the gas meter may be upgraded, especially if your existing one doesn’t have enough capacity to supply the tankless water heater and all your other gas appliances. A tank water heater may use 30K British Thermal Units (BTUs) per hour while a tankless system may require 90K to 130K BTU/H.

Your local gas company can check the meter to determine if any updates are needed.

You’ll also need a professional to run a 1-inch gas pipe from the meter to the water heater, along with another gas shutoff valve. A stainless steel exhaust pipe is installed. It includes a fan that pushes out air and condensation. High-efficiency units can be served by a plastic pipe. If you live in a colder climate, installing a damper protects the system from cold air.

Electrical work may be necessary as well. Gas units use 120 V electrical power and need a dedicated outlet or junction box. However, an electric water heater requires a 240 V circuit along with a subpanel (plus wiring between the two). 

Remove the Old Water Heater

Before removing the water heater, the water supply and gas lines are turned off. The water is also drained from the tank. A heat-rated hose is used to drain the system (a typical garden hose will be damaged). Opening a hot water faucet releases pressure. Once the tank is drained, the water and gas lines are disconnected, which typically requires a pipe wrench or channel-type pliers. The unit is then disposed of per local codes and regulations.

Set Up the Pipes

A location is chosen for tankless water heater installation. The technician drills a hole in an outside wall close to the water heater. Through here, PVC pipes for the fresh air intake and vent are inserted. A traditional chimney won’t be effective because the flue gas temperatures on a tankless system are too low. Instead, the system can be vented through a rim joist.

The contractor taps into an existing tee if your gas line is the proper size and the unit is being installed where your old water heater was. A gas shutoff valve, tee, and sediment trap are installed. A flexible line is run from the tee to where it can be attached to the unit.

Copper pipe is used for connecting new hot and cold water lines to existing plumbing. The new lines are run to the new water heater and cut and soldered as needed. The copper lines may also need to be deburred and sweated; the plumber will secure the pipe to the wall with bell hangers. An expansion tank may be installed near the cold intake.

Mount the Tankless Water Heater

When installing a tankless unit, the contractor can set it flush against the drywall or plaster. It can also be set into the wall between studs. The unit is mounted according to the manufacturer’s instructions. Water supply and outlet pipes are routed and connected to it and shutoff valves are installed on both lines nearby. Inlet and outlet connections are finalized with union fittings.

To set up the water heater, water valves, and faucets are opened. The electricity and gas are not yet turned on. Water is allowed to run through the unit for a minute or so and then turned off (to purge air from the water pipes and heater). The inline filter is removed, debris is cleaned out, and then the filter is replaced, water valves are opened, and power and gas are restored. The technician then tests the unit to ensure proper operation. 

Install System Valves

During installation, a pressure relief valve is installed. It’s a safety device that opens if system pressure is too high (often due to overheated water). A purge valve is also installed to simplify maintenance. In addition, the plumber can install a crossover valve at the furthest plumbing fixture, which allows a recirculation pump to deliver hot water.

Why Do I Need a Plumber for Tankless Water Heater Installation

Whether you’re upgrading from a traditional unit or replacing a tankless water heater with a new one, extensive water and gas line work is required. There are many safety hazards associated with installing gas and electric water heaters. A licensed plumber knows how to address these and meet permit requirements, comply with code regulations, and satisfy the terms of the warranty. 

Most importantly, they can avoid damage to the equipment and your home. There are also rules for the removal and disposal of old water heaters, which a professional plumber is familiar with. They ensure your old system is taken away safely without violating any regulations.

Contact NexGen

NexGen is trusted for tankless water heater installation and replacement throughout Southern California. Our technicians are fully licensed and insured. They’ll help determine the best model to install, provide a free estimate, and discuss your financing options. We also offer competitive pricing and a price match guarantee, which can help manage installation/replacement costs (these can be offset by increased efficiency and lower maintenance requirements). For more information, call (805) 301-6788 today.

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