Non-Condensing Vs. Condensing Gas Tankless Water Heater – What's The Difference?

26 October 2022
 Categories: , Blog

Choosing a tankless water heater can be a great decision if you want to improve your home's efficiency and enjoy endless, on-demand hot water. However, your decisions don't end when you ditch the conventional tank. Instead, you'll need to make a few more choices about your specific model, such as its capacity and whether you want to select a condensing or non-condensing unit.

While capacity is a relatively straightforward decision based on water usage calculations for your home, efficiency can be a little more complex. Since the biggest difference between mid-efficiency and high-efficiency water heaters is often their non-condensing vs. condensing exhaust systems, it's a natural place to start when learning about the benefits and drawbacks of each.

Efficiency and Exhaust Gases Explained

When dealing with any gas-powered heating appliance, efficiency and exhaust go hand-in-hand. A gas water heater generates heat by burning fuel, but the combustion process produces harmful gases as a byproduct. Unfortunately, those harmful exhaust gases also contain the energy you want to heat your water.

Gas appliances such as tankless water heaters get around this problem using heat exchangers. The hot gases pass through the heat exchanger, which extracts heat energy and transfers it to the water. The more energy the heat exchanger can extract, the cooler the exhaust gases will become. Any remaining heat energy remains in the exhaust gas and escapes into the environment.

In other words, a higher-efficiency tankless water heater will produce cooler exhaust gases, while a lower-efficiency unit will leave more heat behind. These design considerations are essential to understand if you're trying to learn the differences between condensing and non-condensing tankless heaters.

Choosing Between Condensing and Non-Condensing Units

Higher-efficiency tankless heaters are known as condensing units because they extract so much heat from their exhaust streams that moisture in the gas will condense into a liquid. While all water heaters will produce some condensation, these units produce substantially more. As a result, they typically use PVC flues to handle drainage and the potentially acidic condensation.

On the other hand, non-condensing units produce much higher temperature exhaust gases. Due to the high exhaust temperatures, these units can't use PVC, so they rely on more expensive stainless flues. Since non-condensing units will still produce a small amount of highly acidic condensation, the exhaust flues can eventually corrode.

If you're selecting between these two units for your home, a condensing unit will save money over the long run but will almost always cost more upfront. However, you're unlikely ever to face issues with its exhaust system. On the other hand, a non-condensing unit will be cheaper to purchase and install but potentially more expensive to operate.

The best option for your home will depend on your specific priorities and budget. However, if you're looking for higher efficiency and cost is not a concern, a condensing unit will typically provide the best bang for your buck over the unit's life. 

For more information about tankless water heaters, contact a local company.