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Can I Add A Tankless Water Heater To Existing System?

Getting a tankless water heater is quite exciting, as it can give you an unlimited amount of hot water at all times. But if you already have a water heating system, you might be confused if you can install a tankless heater.

So, can I add a tankless water heater to an existing system? Yes! It’s actually better to install a tankless heater to an existing system as you’ll be using the same fixtures but have more water. Besides, if you don’t have a lot of storage, getting a tankless system is highly recommended.

But the process can be a bit difficult to understand. So today, we’ll go over tankless water heaters, how you can add them to your current heating system, the benefits and disadvantages, and more. Let’s begin.

Can I Add A Tankless Water Heater To Existing System?

Yes, you can add a tankless water heating system even if you already have a system. It’ll actually benefit you, as you’ll still be using the same fixtures and units while having a significantly higher supply of heated water.

The higher price to get a tankless water system is justified, too, as it lasts significantly longer than a regular tank heating system. Overall, if you use heated water often, adding a tankless water system is worth it.

But if you lack the space, you could remove your current water heating system with the tank. This can be a bit complicated. So you should call a professional to make sure that your tankless system won’t face issues.

add a tankless water heater to existing system

What Are The Disadvantages Of Having A Tankless Heating System?

A tankless water system has tons of advantages, such as a significantly higher capacity of water, less storage, and ease of use. Nevertheless, it has a fair share of disadvantages, which most people don’t talk about.

So here are all the disadvantages you might face from using a tankless heating system, especially if it’s with an existing system —


First of all, the biggest disadvantage of a tankless water heating system is the price. Although it’s significantly better than a regular water heating system in most ways, it can cost 2-3 times more.

The heater itself can cost between $500 to $1000 most of the time, but the installation costs are often another $1000. Sometimes as high as $1500, depending on where you live.

No Simultaneous Waterflow

Although a lot of people think a tankless water system can give an instant supply of hot water for a long time, that’s actually not true. It’ll heat up about 2-5 gallons of water per minute, which is good enough.

However, it can’t work when there are multiple taps running at the same time. But this is just a minor inconvenience unless you live in a very big house with more than 6 people. So you won’t have to worry about multiple taps staying open for a long time, such as a shower.

Requires Electricity

Unlike traditional water heaters, a tankless water heating system will always require energy to work. This means that if your power goes out, you can’t enjoy hot water. Thus, you might have to use your traditional tank heating system instead for the hot water.

How To Install A Tankless Water Heater To an Existing System?

As you can see from the disadvantages, the most major disadvantage is the price. However, if you have experience with plumbing, you could install the tankless system yourself, saving you more than $1000 worth of labor work.

So here’s a step-by-step guide on installing a tankless water system, even when you have an existing system.

  • Step 1. Cut your water supply and circuit breaker
  • Step 2. Drain your current water heater, as it might interfere
  • Step 3. Remove your front cover, and keep the screws safe
  • Step 4. Mount your heater to the wall with the screws
  • Step 5. Connect all the pipes distributing hot water, according to the manual
  • Step 6. Install your pressure and flow valves
  • Step 7. Bleed your hot water system to remove any air
  • Step 8. Check your screws and electrical connections
  • Step 9. Turn your circuit breaker back on

After that, you’re done. Now you can just check the temperature and if needed, test the various outlets. You can mostly install it with the help of the manual, or get professional help.


If you have other similar queries, you can take a look at these questions we get asked often.

Q: What is meant by a tank booster?

A tank booster is another term for a tankless water heater. It’s called a booster as it can boost your current tank system and increase the water supply while lasting longer and taking less space.

Q: Does it take more electricity to use a tankless water heater?

No, it doesn’t. A typical tank water heater can have a Uniform Energy Factor, or a UEF of 0.94, while a tankless system nowadays will have a EUF of 0.70. This means that it’s not only more energy efficient, but it supplies double the amount of heated water.

Q: How long can it take to install a tankless water heater if you have an existing heating system?

If you get it done by a professional, it can take between 4 to 6 hours to install a tankless water heater, even if you have an existing system. But if you’re doing it yourself according to the manual, it might take longer.

Final Thoughts

So, can I add a tankless water heater to existing system? Yes, you can, and it actually benefits you as you’ll have the same fixtures for the old water heater with the tank. It’ll use less space too, and supply significantly more heated water than a traditional water heater.

However, the biggest disadvantage is the price, as it can cost $500 to $1000 for the heater and another $1000 or more for labor costs. This is double and sometimes even triple the price of a regular heater.

But if you want a constant, reliable supply of hot water, it’s still worth it. You could save some money by installing it yourself, too. With all that said, good luck, and cheers!