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How to Install a Tankless Water Heater? – Only 4 Steps

Fact checked by Stephen Conklin

how to install a tankless water heater

Are you tired of waiting for your water heater to heat up before you can enjoy a warm, soothing shower? Or are you weary of its maintenance requirements? Did you know you can forget these worries if you know how to install a tankless water heater?

Tankless water heating systems provide you with hot water and have a longer lifespan than tank systems. These water heaters are also more economical to operate while saving you space. There is also no worrying about ‘standby losses’ and limited warranties. You also get tax credits.

Are you ready to learn how to perform a DIY tankless water heater installation? Let us get right to it.

Table of Contents

Things You Will Need for This Tutorial

There are not many things you need to install a tankless water heater, especially if you have an electric unit. The best part is that many tankless water heater manufacturers provide their products with installation parts and hardware.

If you install a gas unit, you will need a stainless steel flex pipe, venting ducts, and an appropriate gas line connector.

You might also want to buy additional water pipes and fittings if you must replace the old ones. A screwdriver, wrench, or any other hand tool for fastening hardware is also a must. A heat resistant silicone sealant, hanger brackets, and a bucket will also come in handy.

Steps to Installing a Gas-powered Tankless Water Heater


A conventional water heater with a storage tank is bulky, taking too much space. That is why many families are switching to a tankless system with its space-saving design and the ability to supply hot water on-demand.

Follow the steps below to install a gas tankless heater.

Step 1. Determine the need for necessary permits or clearances.

Do not install a gas tankless water heater without reading the local building code. Some cities and municipalities have strict requirements for fitting a gas-powered heater, typically calling for a licensed professional.

Step 2. Shut off the water and gas supply.


You can skip to Step 4 if you don’t have an old water heater to remove.

Check your water heater’s water supply line for any shutoff valve and close it. If you cannot find it, you might want to turn off the water supply at the main shutoff valve. Open several hot water outlets to drain the water completely and purge air.

You might also want to open the pressure relief valve or pressure reduction valve to help in emptying the water from the storage tank.

Locate your main gas line shutoff valve and turn it off. You should see it next to the gas meter.

It would be wise not to disconnect the gas line without ensuring it is already empty.

Step 3. Remove the existing water heater.

Use the correct hand tool to loosen the fasteners connecting the gas line to the heater. You will also want to disconnect the existing water lines, both at the inlet and outlet ports.

It is often wise to place a bucket underneath the water heater near the water connections. It should help prevent messes if there is still some water left in the pipes.

Set the old water heater aside for proper disposal.

I found an excellent video from HouseBarons showing how to remove gas units. I suggest checking the short film to guide you in your heater uninstallation.

Step 4. Mount the new gas-powered tankless water heater.

Installing a tankless water heater is hassle-free if you read the instructional manual beforehand.

I suggest planning the tankless water heater’s location before you start drilling mounting holes through the wall. It should be near an electric outlet for plugging the device and operate its electrical components. It is also wise to position the heater near your existing gas and water lines.

Always check the new tankless water heater for the mounting hardware. Most manufacturers provide a wall bracket and mounting parts for their units.

Drill holes through the wall and secure the tankless water heater.

Step 5. Install the vent, if needed.

If your tankless water heater can withstand heat and freezing temperatures, you can proceed to connect the cold water pipe.

Unfortunately, most gas heaters have an indoor-use-only design. Hence, you must install a stainless steel vent pipe to draw air and excess heat from your home’s interior and move it outside.

Some heaters are direct-vent units, while others are power vents. If you have a direct-vent heater, you must drill two holes for the intake vent and exhaust vent. A power vent heater only requires one duct.

Check your tankless heater to determine which vent type it has and drill the necessary holes for your appliance. Ensure a tight joint seal between the unit and the duct and between the tube and the wall.

Step 6. Connect the water lines.

The next step in tankless gas water heater installation is connecting the water lines.

Your new tankless unit will have two connections: a cold intake for passing cold water to the heater and an outlet dock for conveying hot water to the house’s water distribution system.

Some on demand hot water heaters call for compression fittings, while others may use proprietary fastener technologies.

You might also want to solder copper piping if you use a copper pipe for the hot water pipe. Check the connections in the cold water lines that bring cold water to the tankless model. Secure the joint between the pipes and the tankless unit with a sealant.

Step 7. Connect the gas line.

Making gas pipe connections is the trickiest. You court domestic fires and other problems if you do not observe the correct gas line connection procedure. That is why many experts do not consider gas powered water heater installations a DIY project.

First, secure an appropriate gas line connector for the existing gas line. Next, fix a flexible gas supply line to the connector while securing the other end to the heater’s gas port. You can also use a threaded black iron pipe if you want.

Ensure to tighten all connections or fasteners before heading to Step 8. Check if the gas meter is functioning properly.

Pro Tip: Check with your local gas company for recommendations on making gas line connections and if you need more gas to heat water. I also suggest replacing the current gas line with a new gas supply line.

Step 8. Check for gas leaks.

There is only one way to ensure a secure gas line connection to your instantaneous water heater: test it.

I recommend getting a gas leak sniffer to help you check for leaks. Alternatively, you can use the old-school method of applying soapy solution along the gas line.

Open the gas line shutoff valve and turn on your gas leak detector. You should hear an alert or a visual cue from the device signifying a possible leak.

If you prefer the low-tech method, prepare a soapy solution and spray it along the gas line and the gas shut off valve. Check the connections, too. If you see bubbles popping, you may have a gas leak.

If you see gas leaks, you might want to retighten the connections. You can also replace the gas line if a leak occurs along its length.

Here is a fun video from Appliance Princess answering questions about detecting and fixing leaking gas. While the video references a tank water heater system, you can use the information nuggets to help you check for gas leaks in your tankless heater.

Step 9. Connect the electrical system.

Many people think there is no such thing as tankless gas water heater electrical requirements. After all, the device runs on natural gas or propane and not electricity.

The modern gas tankless heater has a sophisticated PC board, an electric thermostat, an electronic ignition system, and a few other components that run on electricity.

The good news is your water heater may already have a power cord, which you can plug into an electrical outlet. If the outlet is beyond the wire’s reach, you might want to install a new electric outlet near the water heater.

Step 10. Test the gas tankless water heater.

The tankless water heater installation is near complete.

This Old House prepared a video about replacing an old gas tank water heater with a tankless version. I suggest checking the short film to make your installation adventure more worthwhile and pain-free.

Step 11. Dispose of the old gas tank heater according to local laws.

Check your local laws for guidelines on how to dispose of your old gas water heater tank. Some cities, municipalities, and states have strict regulations on the management of such devices.

For example, Californians cannot dump their dilapidated gas tank water heaters in an ordinary garbage bin. Gas heaters have mercury-containing pilot light sensors that can harm the environment. The best way to dispose of these products is by working with a waste management and recycling company.

Steps for Installing a Tankless Electric Water Heater


You are fortunate if you wish to install an electric tankless water heater instead of a gas unit. The procedure is more straightforward because there are no gas lines to worry about.

Step 1. Check local building laws.


It would be best to check the local building code for adding an electric tankless heater. Some municipalities and cities have specific electric tankless water heater installation requirements.

Step 2. Remove the old electric tank water heater.

Shut off the water supply, open the pressure relief valve, and unplug the power cord before removing the water connections using an appropriate hand tool. Remove the old tank heater and store it in a safe place. You can also give it to a recycling company if you want.

Step 3. Install the electric tankless water heater.

Mount the electric heater on the wall using the bracket and hardware provided. Ensure to tighten all copper pipe fasteners before connecting the water supply line to the heater’s inlet port. Secure the other water line to the device’s outlet port.

There is no need to create holes for venting because an electric tankless unit does not require any.

Step 4. Test the water heater.

Open the main water supply shutoff valve and the water heater valves. Next, plug the electric instantaneous water heater in an electrical outlet. Switch on the device and wait several seconds, allowing incoming water pressure to build up.

Turn on the shower or a hot water faucet and check if the water is warm enough for you.

Pro Tip: It would be best to check your electrical service panel or circuit breaker panel. Some electric tankless water heaters draw substantial electricity, which your electrical breaker box might not be able to accommodate.


Tankless water heaters give you many advantages, including instant hot water and a continuous hot water supply. You also get to enjoy tax credits from the government, lower operating costs, more space, zero standby loss, and more.

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