Condensing vs. Non-Condensing Water Heater

The terms condensing and non-condensing are often thrown around when we talk about tankless water heaters, but what exactly do they mean? It can get quite technical and confusing, but in this article, we’re going to keep it as simple as possible and outline the differences between these two types of tankless heaters.

We’ll also talk about the pros and cons of condensing vs. non-condensing water heaters and which is the better of the two.

What is Condensation in a Tankless Water Heater?

Condensing water heater inside

Inside the Rinnai RUR98iN Condensing Water Heater. Check Price Here.

Tankless water heaters don’t store water in a tank and heat it up, like storage tank heaters. Instead, they work very hard and fast to heat up water as it runs through the heat exchanger in the system. This is heated using very strong combustion, which creates hot gases including water vapor or steam. This is a natural by-product of the process, and results in condensation as the steam/vapor cool down. Condensed water has a low pH and its acidic nature makes it harmful for the unit as it’s corrosive.

How this condensation is dealt with is what differentiates a condensing vs. a non-condensing tankless heater.

What’s a Non-Condensing Tankless Water Heater?

Non-condensing tankless water heaters simply get rid of the hot condensation, by pushing it out of the unit and into the ventilation system. Because these gases are very hot (around 300oF) and acidic, the ventilation system needs to be able to withstand their harmful impact. This means using corrosion-resistant venting materials like stainless steel alloys, because regular materials like PVC vents may not be able to deal with the heat of the gases.

This also means that the hot gases which haven’t contributed to heating the water, is essentially wasted energy. The gases used up energy and then was ejected from the system, providing no benefit. This is why non-condensing units are less energy efficient (around 80% energy efficient) because around 20% of the energy they use is wasted on the condensation process.

What is a Condensing Tankless Water Heater?

Best tankless water heaters

Condensing tankless heaters are much more energy efficient because they put these gases to good use. What these systems do is to use the heat of the exhaust gases to contribute to water heating by using a second heat exchanger. The much cooler vapor (around 100oF) and gases are sent out through the vent. This process uses up much of that wasted 20% of energy, with a total energy efficiency of up to 98%.

However, there’s a caveat. Because the condensation is captured inside the unit, it results in water collection. This can cause corrosion to the inside of the water heater. This is why condensing units have to be made of much higher quality non-corrosive materials, to ensure that the tankless heater can live out its lifespan.

So what happens to the water collected inside the unit?

Because it’s highly acidic and damaging, the water is first neutralized using a process of filtration or dilution. The water can then be expelled from the unit.

This process has several implications:

  • Condensing units are more expensive due to the quality of materials they need.
  • The venting for condensing units is not as expensive as for non-condensing units, but it’s still a good idea to invest in non-corrosive venting materials like stainless steel alloys.
  • Condensing units reduce your utility bills with their higher energy efficiency.
  • However, they require more maintenance, such as flushing the units and cleaning the condensation trap and the filters.
  • Sometimes the climate/temperature/environment may not allow condensation.
  • These models are typically a little larger than non-condensing due to the extra parts inside.

Which Should I Buy?

When weighing the pros and cons of both types of water heaters, it’s clear that condensing water heaters have more benefits and are more effective. However, a closer look will show that there’s a trade-off between these two units, which makes it a little less clear-cut.

After all, if non-condensing units wouldn’t still be on the market if they didn’t offer some benefits. So how do these compare in terms of pros and cons:

Non-condensing units are smaller, less expensive and easier to maintain. On the flip side, they require expensive venting units and are less energy efficient.

Condensing units are more energy efficient and require less expensive venting units, but their upfront costs are higher, they’re typically larger and require more maintenance depending on the quality of the water you use.

Which you buy depends on your specific requirements and calculations regarding purchase, installation, maintenance and energy costs.

Before You Buy a Tankless Water Heater

The decision of whether to buy condensing or non-condensing a tankless water heater is only one consideration you have to make when choosing a tankless water heater.

There are many other important things to consider, including whether to choose gas or electric, the size of the unit, the cost of purchase and installation, the brand, the climate you live in, and so and so forth.

In our detailed guide on how to buy a tankless water heater, we tackle all these questions as well as reveal the best tankless water heaters (electric and gas) on the market. Hopefully, it’ll be able to help you make an informed choice.

If you want to learn more about tankless heaters vs. storage tank heaters, check out our article here.

For all the top FAQs we get asked about tankless water heaters, go here.

Clean Water Gear
Shopping cart