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Condensing vs. Non-Condensing Tankless Water Heater

Worker Repairing Tankless Water Heater

Water heaters have evolved into tankless units. They now provide instant hot water without needing a storage tank. Since tankless water heaters offer many pros, they are gaining in popularity.

If the debate before was about tank vs. tankless water heaters, now the discussion is about condensing vs. non-condensing tankless water heaters.

But what sets them apart? This article will explore the key differences between condensing and non-condensing tankless water heaters to help you make an informed decision for your home.

How Does a Tankless Water Heater Work?

How Does a Tankless Water Heater Work?

Before diving into the distinctions, it’s essential to grasp the core mechanism of tankless heaters. These devices heat water directly as it flows through them, eliminating the need for a storage tank.

When you turn on a hot water tap, cold water travels through the unit, where a gas burner or electric element instantly heats it.

This design can be more energy-efficient than traditional storage water heaters because it eliminates the need to heat a water tank, even when not used continuously.

Starting the Flow:

When you turn on a hot water tap (or start an appliance that uses hot water), cold water flows into the tankless unit.

Flow Sensor Activation:

A flow sensor within the unit detects this water flow and activates the heater.

Heat Exchange:

Gas-Powered Tankless Heaters:

For gas-powered units, a gas burner ignites to heat a heat exchanger. The incoming cold water circulates through this exchanger and is heated before it’s directed to the hot water tap.

Electric-Powered Tankless Heaters:

For electric units, electric elements heat the incoming cold water.

Temperature Measurement:

A thermostat or thermocouple measures the outgoing water’s temperature to ensure it reaches the desired temperature set by the user.


If the water isn’t hot enough, the unit will adjust by increasing the flame in the gas burner or the electric current to the elements. Conversely, if the water is too hot, it will reduce the heating intensity.

Continuous Supply:

As long as the hot water tap is open, the tankless water heater will continue to supply a steady flow of hot water. This is a crucial difference from traditional tank heaters, which can run out of hot water once their stored supply is depleted.


Once the hot water tap is turned off, the unit detects the drop in water flow, and the heating element or burner shuts off.

Learn the Core Differences between Condensing vs. Non-Condensing Tankless Water Heater

1. Energy Efficiency & Operation:

Condensing Water Heater:

Condensing heaters are more energy-efficient, boasting an efficiency rate of up to 98%. This is because they utilize two heat exchangers. The primary one heats the incoming cold water, while the secondary one captures heat from the exhaust gases, which would otherwise be wasted.

Non-Condensing Water Heater:

Operating with a single heat exchanger, these units typically have an 80-85% efficiency rate. The hot exhaust gases are vented outside immediately without additional use (this thermal energy is wasted).

2. Venting Requirements:

Keep the Area Around the Water Heater Clear

Condensing Water Heater:

The exhaust gases from these heaters are cooler, thanks to the secondary heat exchanger. This means they can be vented using affordable PVC pipes rather than the specialized stainless-steel ones required for non-condensing units.

Non-Condensing Water Heater:

Non-condensing water heaters release hotter exhaust gases, necessitating high-grade stainless-steel venting to handle the high temperatures.

3. Cost and Long-Term Savings:

Condensing Water Heater:

While the initial purchase price may be higher, the savings from energy efficiency can offset the cost over time. Additionally, the cheaper PVC venting can reduce installation costs.

Non-Condensing Water Heater:

Typically cheaper upfront, they may incur higher operational costs over the long run due to lesser efficiency. Also, the specialized stainless-steel venting system is more expensive to install.

4. Durability and Maintenance:

Technician Providing Maintenance to Tankless Water Heater

Condensing Water Heater:

The condensation process produces acidic water, which is neutralized and drained off. However, this can lead to potential internal corrosion. Regular maintenance and using high-quality materials in their construction can offset this drawback.

Non-Condensing Water Heater:

These units have been around longer and have a more straightforward design, which can translate to fewer maintenance concerns. But like all appliances, regular check-ups are essential for longevity.

Click here for general tankless heater maintenance tips to keep your unit working at its peak.

Which Tankless Water Heater is Right for You?

The decision largely depends on your priorities:


If you’re looking for an affordable, upfront option, non-condensing heaters might be the way to go. But if you’re thinking long-term, the energy savings from a condensing unit might justify its higher initial cost.


If the highest efficiency is prioritized, condensing is the clear winner.

Installation & Maintenance:

Condensing units have an edge because of their PVC venting for more accessible and cheaper installation.

However, a non-condensing unit might appeal more if you’re wary of potential internal corrosion and the associated maintenance.

In conclusion, condensing and non-condensing tankless water heaters have pros and cons.

The choice should reflect your household’s needs, budget considerations, and long-term plans.

It’s always a good idea to consult professionals and check the latest reviews and ratings before purchasing. Doing so ensures that you invest in a system that offers both efficiency and reliability.

Ready to get a tankless water heater, ensuring you receive an affordable and high-quality installation? You just need to contact BG Plumbing! Our professional plumbers guarantee that your tankless water heater will last for decades to come, working at its best.

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