Colton Deck

By: Colton Deck on January 26th, 2023

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What is a Tankless Water Heater Heat Exchanger?

Tankless Water Heaters

So, you’re thinking about buying a tankless water heater but don’t know the first thing about them. Well, the good news is that they’re relatively easy to break down. If you want to get a grip on what makes tankless water heaters tick, the heat exchanger is the perfect place to start. 

For over 15 years, we’ve been servicing Los Angeles County and its surrounding areas to ensure homeowners have reliable hot water from their tankless water heaters. In that time, we’ve grown to understand tankless water heaters inside and out. Despite advancements in heat exchanger technology, the core functionality remains the same as it has for years. 

In this article, you’ll get an explanation of what a tankless water heater heat exchanger is, how they work, the different types available, and what can happen if your heat exchanger isn’t functioning properly. 

Let’s jump in by learning how heat exchangers serve as the core of the tankless water heater design. 


What Is a Tankless Water Heater Heat Exchanger?

On the surface, the answer to what a tankless water heater heat exchanger does is quite simple. A heat exchanger is responsible for heating the water that flows through your home. Without the heat exchanger, you essentially have a decorative box mounted to the wall. But things get slightly more complicated when we go beyond that simple definition. 


How Do Tankless Water Heater Heat Exchangers Work?

Tankless water heater heat exchanger against white background


Moving past the simple definition of a heat exchanger, let’s briefly look at how they work. 

A tankless water heater heat exchanger has two components: the igniter flame and the heat exchanger coils. One more crucial element that sits outside the heat exchanger is the flow sensor. Let’s go step by step to see how the heat exchanger and flow sensor work together. 

  1. Cold water enters the tankless water heater. 
  2. The water passes over the flow sensor. 
  3. The flow sensor signals the igniter flame to light.
  4. The igniter flame heats the coils of the heat exchanger to the preset temperature. 
  5. Heat transfers from the coils to the water flowing through them.
  6. Warm water exits the heat exchanger and travels to the fixture that causes the demand. 

Pretty simple, right? Things got slightly more complicated, but there’s really nothing much to it other than that. 

So, that’s it, then? Nothing else to it? Well, not quite. You have a couple of options when it comes to buying a tankless water heater model for the heat exchanger. 


Types of Tankless Water Heater Heat Exchangers

For decades, copper-based heat exchangers provided families around the country with hot water on demand. But recently, stainless steel heat exchangers gave the reigning champ a run for their money. But what’s the difference between the two


Stainless Steel Heat Exchangers

Starting with the newest option on the market, stainless steel heat exchangers offer a few improvements over their predecessors. But, as with anything new, you can expect a bit of a price gap between the two material types. 

Stainless steel heat exchangers hold up better against hard water, which is common in Southern California and other regions. The added durability means more time between regular maintenance calls and a longer lifespan in general. 

Going along with a longer lifespan is the longer warranty terms you’ll find manufacturers offering. While the typical warranty period is 12 to 15 years, stainless steel heat exchangers can carry up to a 25-year warranty. 

Stainless steel-core tankless water heaters also offer maximum efficiency. If you live in California, this quality means you qualify for the full state rebates. Likewise, stainless steel-core models will net you the maximum federal tax credit. 

These heat exchangers aren’t perfect, though. You’ll likely pay from $500 to $1,000 over the asking price of a copper model. Additionally, stainless steel isn’t quite as conductive as copper, meaning you’ll have to wait a few extra seconds to get hot water from any given fixture. 

With these factors in mind, let’s take a look at the tried-and-true heat exchanger option. 


Copper Heat Exchangers

Despite being the older option on the market, copper heat exchangers aren’t going anywhere any time soon, and with good reason. While stainless steel has several advantages over its predecessor, copper just can’t be beaten in certain areas. 

One of copper’s most significant claims to fame is its conductivity. Copper heats up faster than stainless steel. This aspect means you won’t have to wait as long for your water to warm up since the heat exchanger will get the water up to temperature faster than stainless steel. 

Another win for copper-core models is the greater variety and accessibility. You’ll find copper-core tankless water heaters for any home size, indoor or outdoor, and be able to find them at local hardware stores or supply houses. While stainless steel models are still making their gradual rise, copper-based tankless water heaters are well-established in many stores. 

You’ll also pay less than you would with a stainless steel-core model. This one is a double-edged sword since you won’t get the 25-year warranty with a copper model or added protection against hard water. 

Speaking of hard water, this is the copper heat exchanger’s worst enemy since copper is prone to corrosion. Because of its lesser durability, you’ll need to install water treatment and perform annual maintenance to ensure that your tankless water heater reaches its maximum lifespan. 

We’ve discussed each option in depth, but that doesn’t mean either option is immune to the pitfalls of heat exchangers in general. What happens when something goes wrong with your heat exchanger? 


What Happens When a Heat Exchanger Breaks?

The most common issue you’ll face when it comes to your tankless water heater’s heat exchanger is a leak. A leak in a tankless water heater clearly indicates that the unit isn’t working properly, and you’ll need to get a technician out there ASAP. 

If you don’t notice the leak, you may be alerted by colder water, error codes on the unit itself, or power cycling. Many units have a preventative shutoff that will cut the power to the unit to prevent further damage to electrical components like circuit boards. 

Basically, if your heat exchanger goes, so does your hot water. This potential issue is the biggest reason to keep up on annual maintenance and ensure everything stays in working order. 


Now You Have a Handle on Tankless Water Heater Heat Exchangers

We’ve covered what a heat exchanger is, how it works, the types of heat exchangers on offer, and what happens when they break down. Now, you better understand what you’d be investing in if you went the tankless water heater route.

Monkey Wrench Plumbing, Heating & Air has worked with tankless water heaters for well over a decade, so you can trust us when we tell you that they are the life behind a tankless water heater. While there have been improvements, there’s no going wrong with either material. Still, it pays to know what you’re getting into and to be able to make an informed decision you can stand behind. 

If you’re ready to schedule a consultation for your home, call us at 310-853-8690 or book online through our Tankless Water Heater Page. Or, if you’re curious to know more, read up on how tankless water heaters work and the common issues they face.