How to Install a Tankless Water Heater

Oct 21, 2021

Upgrading to a tankless water heater is a major decision, while deciding how to install a tankless water heater is a bit more straightforward. Installation is no small task; it requires a great deal of expertise to accomplish a professional quality installation. Here we will explain the steps of how to install a tankless water heater to give you a clearer picture of the process.

1. Service Your Gas Line

If installing a gas unit, your gas line and connection may need to be upgraded. A plumber will examine the system to determine whether a new gas line must be installed. A tankless water heater requires a combustion air source and ventilation to safely remove combustion gases. Also, an electrical outlet must be nearby to power the unit.

A larger gas pipe is often required (if you have a ½ inch line, you may need a 1-inch line). That’s because tankless systems often use 90K to 130K BTU/h, while a standard water heater tank may run on just 30K BTU/h.

2. Disconnect Your Old Water Heater

Before you remove the old unit, determine the type of system you need (gas or electric) and what size tankless water heater to install. To remove the old unit:

  • Turn off the water supply and gas connection.
  • Drain the water out of the tank, using a heat-resistant hose.
  • Open a hot water faucet, which allows more complete draining.
  • Remove the gas line, usually by disconnecting the union fitting first.
  • Disconnect the water lines from the top of the heater.
  • Follow the disposal guidelines of your local sanitation or recycling company.


3. Mount Your New Tankless Water Heater

First, choose a location to place the unit. The best place is somewhere where you can vent it to the outside. Make sure to have proper clearance on all sides of the heater and follow local codes pertaining to permitted distances from doors and windows.

Next, build a mounting box to place the unit about four inches out from the wall. A sturdy box made of 2×4 lumber and ¾ inch plywood will do, and anchor it to the foundation wall with masonry anchors. Follow the manufacturer’s instruction for mounting the unit.


4. Run the Piping

Unless you have experience running gas pipe connections, it’s safer and more practical to have a licensed contractor do the work. Here’s a look at the process of making the appropriate connections for your tankless water heater:

  • Have a professional run a larger gas line, as required, and run it from the gas meter to the unit.
  • Thread black iron pipe to extend your gas line to the heater.
  • Install a gas shut-off valve, tee, and sediment trap (the valve and trap connect directly to the unit).
  • Run the gas supply line from the tee to the heater’s gas line.


5. Install the Water Lines

To start the process:

  • Drill a hole outside your house near the water heater.
  • Run PVC pipes through the hole for the fresh air intake.
  • Connect new hot/cold water lines to existing ones with copper pipe.
  • Run these lines to the new water heater.
  • Clean the area with a sanding cloth, then cut the copper lines (debur any cut sections).
  • Clean the inside of each joint and end of pipe section (with a sanding cloth or pipe fitting brush).
  • Secure the pipe against the wall with bell hangers.


6. Connect the Pressure Relief Valve

A pressure relief valve releases pressure if the water overheats. You can also use the valve during maintenance to purge the system. To install one, follow the manufacturer’s instructions. Then turn the water supply on and check for leaks. Do the same when turning on the gas. If there are no leaks, turn the gas line off and complete the installation.


7. Install an Exhaust Vent

Tankless gas water heaters require a vent kit. The components used depend on the manufacturer. Stainless steel vent pipe is typically used, while some models use PVC pipe. Either pipe must be connected to the vent hood on the outside (and remember to replace any shingles or siding you removed while creating the vent opening).

8. Turn on the Water, Gas, and Power

Once the water heater is plugged in and hot water pipe is insulated, turn on the gas and follow any manufacturer-recommended start-up procedures. When your tankless water heater is successfully installed, you can benefit from:

  • Its small, compact size. The unit may fit out of the way in the basement, garage, or utility closet.
  • Energy savings. You could potentially save as much as 70% on your heating bill.


Contact Elmer’s Home Services

Our technicians are knowledgeable in all aspects of tankless water heaters. From answering questions such as “What size of tankless water heater do I need?” to how to connect and use the system, they can assist you every step of the way. We can also install a single-fixture or whole house tankless water heater for San Antonio homeowners. Call 210-570-1717 to learn more.

If you are experiencing any of the signs that your water heater needs repair or replacement, don’t hesitate to call a professional.

Elmer’s Home Services in San Antonio TX can help you assess the situation and make the best decision for your needs. We have experienced plumbers and quality service, so you can get back to enjoying hot showers and baths in no time. 

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Call: (210) 570-1717

Headquarters: 9710 N Interstate 35
San Antonio, TX 78233

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About Elmer’s Home Services

Our business provides water heater repair, emergency plumber services, and plumbing repair in San Antonio, Texas. We have proudly served over 20,000 customers. Our professional plumbers are punctual and take pride in providing reliable and affordable home services to our neighbors.

Discover the difference in our services when you get it done “The Elmer Way”. Call us today to get more information!