Condensing vs Non Condensing Tankless Water Heaters

If you are looking to buy a new tankless water heater, the question of condensing or not condensing is bound to come up at some point. What is the difference between these two types, and how can we tell which one best matches our needs?

Technical Background

Condensation is the process of vapor transforming into a liquid state which is something that happens when hot gas comes in contact with a cold enough surface. In tankless water heaters, water can turn into steam very quickly due to the intense heat that raises its temperature in just a couple of seconds and as it passes through the combustion chamber piping. The produced exhaust gasses from this heating process will gradually turn back to being liquid as they cool down by passing through the exhaust pipes. The problem with that is that the acidity of this condensations is quite strong, causing corrosion onto the ventilation parts or network.


In order to avoid this corrosion, non-condensing water heaters employ a direct kind of exhausting system that takes the produced gas outside and as promptly as possible. The benefit of this is that the heater and ventilation parts or network will be kept in a good condition for a long period of time, as acidic condensations won’t be a problem for the inner parts of the heater. The downside is that their operational efficiency is intrinsically low since the energy that was required to turn the liquids into gasses in the first place is wasted, and this is reflected by the fact that the exhaust gasses, in that case, are typically of the temperature range of 300 Fahrenheit. Even the most optimized and efficient non-condensing units won’t yield an energy efficiency that goes much higher than 80%. Finally, the ventilation used for the steam exhaust must be made out of corrosion-resistant stainless steel alloy which is generally a very expensive type of material.


The condensing type of water heaters are those that use a set of tools to extract the excess heat from the produced exhaust gasses and put it back into the water heating process in a form of re-heating cycle. The obvious advantage of this type is the amazing energy efficiency that can go up to 98%! The side advantage is the lower exhaust gasses temperature in the range of 100 Fahrenheit that allows the use of cheaper ventilation materials such as PVC plastics. The disadvantage is that due to the additional systems and the complexity of the design, these tankless water heaters are generally more expensive to acquire and may require more often maintenance sessions.


Non-condensing water heaters are simpler to maintain and cheaper to buy, while the condensing ones are cheaper to operate and more environment-friendly. In this comparison, the condensing heaters are objectively better, but since they cost more it’s all about personal preference in the end. If you want to set up a cheap heating system that is robust and reliable, combine a quality ventilation system with a non-condensing water heater. If money is not a problem, then buy a non-condensing heater from the renown and experienced manufacturer and you’ll enjoy a guaranteed ROI in a very short time.