Informational Guide

How To Install A Tankless Hot Water Heater

Learn how to install a tankless hot water system into your home with five easy steps!

by Matt Moran

For many people, running out of hot water in the home is a regular occurrence. In the modern, technological age this should be a thing of the past, and we shouldn't have to worry about hot water suddenly running cold when we have family or friends visiting.

Tankless hot water systems are the solution to this problem, offering you hot water on demand. Despite providing hot water consistently, they aren't running all the time. This allows you to keep your bills low, and in some cases, they can even reduce your overall utility costs. Our full guide to the top tankless water heaters can be found here.

In this article, we'll explain what you need to consider before installing a tankless hot water system, and the best way to go about doing it in your home. This will help you to do it safely and efficiently, and hopefully gives you and your family access to a consistent flow of hot water that won’t run out.

Stiebel Eltron Tankless Electric

When considering the cost of the unit itself, you should factor in any costs associated with installation. The tankless hot water system can seem complicated at first, but it's actually more straightforward than it may seem.

First, you'll need to consider which type of tankless hot water system you’re going to be installing and using. A single point system is generally the cheaper and simpler option but only provides the instant hot water for one appliance or room. A whole system tankless heater will provide this for the entire home, but they are more expensive to buy and install.

If you are looking to get a professional, then a plumber will probably cost between $500 and $1,000. This is totally dependent on your local rates, but on average, a plumber will charge around $85 per hour for labor. If you have a good relationship with your local plumber and have a lot of work done, then you may be able to negotiate a better rate.

If you choose to install the tankless water heater yourself, then it will save you on those labor costs. Many of these systems will come with all the parts needed, so you may just need to spend up to $100 on the necessary tools. Installing a system like this is certainly doable if you have the experience, but if you make a mistake, it could impact any warranty. This could cost you money in the long run.

In some cases, you may need to rewire part of your home to accommodate the system. This can cost upwards of $2,000, and you will need a professional to certify the work. It's worth scoping this out early to avoid any surprises.

All of these installation costs are on top of the price of the unit. While it is cheaper to do it yourself, if you aren't confident, then you should definitely consider getting a plumber to help out.

Installation Considerations For Hot Water

Gas Line

If you are installing a gas-powered tankless water heater, it's crucial to consider how they work. Your tankless water heater will need more power to work effectively, typically around 120,000-190,000 BTU.

This is potentially up to 5 times more than your existing unit and may require that your gas line size needs to be increased from ½ inch to ¾ inch. You will likely need a professional to carry out an assessment on this and to help you with the work if required.


Getting the right ventilation for your tankless hot water system is essential for it to work correctly. This means you’ll have to carefully consider where your unit will be located because it needs to be able to reach the outside world.

There are a variety of different options to properly vent your tankless hot water system ranging from direct venting to concentric venting. You can even look into the possibility of installing your system outside. Scoping out and deciding how you will vent your unit is one of the most important steps in the installation process.

Water Hardness

If you live in an area that suffers from hard water, then you should carefully consider how you can protect your tankless water heater going forward. High mineral content in the water can cause limescale damage internally.

A scale inhibitor system can be installed directly into your tankless water heater which will filter out limescale before it enters the system. This can help protect your unit and keep it working effectively for longer.

Installation Safety Guidelines

Even those experienced with DIY projects may have some challenges installing a tankless water heater system. There are some safety precautions you should always take during installation and afterward to make sure you protect yourself from any harm.

For the installation, you will be handling some power tools, and there may be a need to use flame and do some soldering. All of this should be done with the greatest of care, and you should consider hand and eye-protective wear throughout.

When removing an existing system and installing a new one, you need to make sure all power is completely shut off. This is a live electrical system and ultimately could cause you injury if it's still connected when you do work.

Before installation, or certainly before you switch the new system on, you should be conducting a full review of the scope of the change. When any wiring is taking place, you need to make sure that your existing setup will be able to deal with the load.

Otherwise, it could lead to short-circuiting, which can lead to an electrical fire starting. In a similar vein, you should get somebody else to verify all work before it's switched on. Any gas connections can be dangerous if not done correctly, and faulty plumbing can lead to real issues. Even if you aren't paying a professional for the work, it may be worth getting them to assure it.

Any DIY work will present some risks and hazards, and the trick is being aware of them and managing them. Taking this one step at a time will help ensure you do everything needed and don’t harm yourself along the way. 

If you do not wish to do this job yourself then we recommend getting a local plumber to do the job. You can find free quotes from your area by filling in the form below.

How to Install a Tankless Hot Water Heater

  • 1
    1. Remove the Old Heating System
    First, you will need to remove the current system. Start by turning off your mains to your home and then disconnect the supply line into the device. Some residue water may be in the pipes so you may want to put towels or newspaper down. You should then disconnect the heat source either by disconnecting the plug (for electric-powered units) or closing the supplier valve for gas units.Once everything is disconnected, you can physically remove the unit. It's worth checking your local regulations in case you have to dispose of it in a specific way.
  • 2
    2. Measuring and Cutting
    You should first work out exactly where your new device will be residing in your home. Some states will have regulations about where your tankless water heater will need to be, and it's worth checking beforehand, a professional should certainly know this.You should then measure the distance to the plumbing and power connections to make sure they reach. You can cut and trim the pipe down as needed so that it fits into the new system.
  • 3
    3. Drill the Holes
    First, you'll need to drill a hole for the venting system. This will need to go all the way through to the outside of the house so you'll have to position the system accordingly. Without proper ventilation, your water system may not work well and can be a safety hazard, so you may want to consult a professional before proceeding.
  • 4
    4. Install Your Hot Water System
    Once all of the different preparation steps are done, you should look to fit your tankless hot water system. You should first mount it in position and connect the cold water supply pipe. You should then connect all the hot water outward pipes and make sure it's all secure. PVC pipes into the ventilation system should be connected up, and the power source should also be connected.
  • 5
    5. Checking Flow and Temperature
    Finally, you need to check the full system. Switch on the power and run some cold water through the system. After a few minutes, you should be getting consistent hot water output. Check around your home to make sure the flow and temperature are working and examine the unit itself to make sure there is no leakage.

Each of these steps is crucial in ensuring your tankless water system is installed correctly. The video below gives a full guide from start to finish on how to fit your tankless hot water system.

Hot Water Maintenance

In order to get the maximum utility from your tankless water heater system, you should perform regular maintenance to keep it running effectively. Limescale can be a real issue to your system as the minerals can build up internally and stop it working. It's essential to know how to clean out your tankless heater system thoroughly.

You should first switch off the mains and disconnect all power sources. You can then carefully unscrew the lid of the unit and remove the purge port valves. Attach the hosing lines and pour about 2.5 gallons of white wine vinegar through the system. This will help to clean out the unit entirely, and the acidic properties will help remove any blockages or build-ups.

While this is going on you should locate your internal filter and scrub it clean, before replacing it back in the water heater. You should then fully flush out the system with water before putting the whole unit back together again.

Regular cleaning should be done every month if possible, and you can invest in some preventative measures, like a scale inhibitor system, to help stop the issues before they start.


A tankless hot water system offers a lot of benefits to you and your home. Having instant hot water on demand is vital to any family. After all, nobody wants to end up standing in a cold shower. While tankless hot water systems can be expensive, they really are an investment in an important home upgrade.

Installing a tankless hot water system isn't the easiest DIY job in the world. There are a lot of different things to consider, and for all major electrical changes, you will need professional certification. That being said, if you have experience with plumbing or DIY projects, then you should definitely be able to handle it.

Make sure you take all the safety precautions and if you run into trouble then don't be afraid to call in professional assistance, as this could save you money in the long run.

Matt is a freelance writer, English graduate, & keen traveler from the UK. As a specialist plumbing expert, he enjoys writing about everything there has to do with at-home plumbing products & related problems. When he isn’t writing, he’s usually drinking coffee or planning his next adventure. In his spare time, he also runs his own blog all about digital nomad life.