Condensing vs Non-Condensing Tankless Water Heaters

In this article, we have discussed Condensing vs Non-Condensing Tankless Water Heaters based on efficiency, cost, noise, power usage, life, load, safety, maintenance, usage, etc.

Tankless water heaters are a great solution for homes in the United States that have limited space or don’t want to deal with storing large amounts of hot water.

There are two types of tankless water heaters: condensing and non-condensing. Condensing units gather the steam from your home’s exhaust into a coolant which is then cooled down by an exterior fan; this allows you to use more energy-efficient appliances because they do not needlessly waste gas or electricity heating up the air around them.

Non-condensing units work like any other traditional heater, using all collected gases inside for heating purposes. Condensing models tend to be more expensive but will save money over time due to their increased efficiency ratings.

Check my article on outdoor tankless water heaters, maybe it will help you in making a purchasing decision.

Condensing vs Non-Condensing Tankless Water Heaters


A condensing unit will typically have a 99% efficient rating when it comes to energy use. A non-condensing tankless water heater will have an 85%-88% efficient rating.


Non-condensing units can be very noisy if they are not installed correctly, as the sudden rush of air from the exterior fan will make a noticeable humming sound from time to time. This can be very frustrating if it is installed in close proximity to your bedroom or other quiet areas of the house. Condensing units are not typically found to be noisy, as they use forced air for cooling purposes rather than relying on fans inside the unit itself.


Although condensing tankless water heaters cost more money upfront, they will eventually pay for themselves in savings on your electrical and gas bills. If you live somewhere that requires a lot of hot water to be used at once (for example a family with multiple children) then the initial investment might be worth it to avoid constantly running out of hot water.

Flow rate:

Non-condensing models tend to have a slightly faster flow rate because of the way they work, but condensing units are typically no slower than their non-condensing counterparts


Condensing units have a longer average life span, and are typically able to last up to 15 years without the need for replacement. 

Power Usage:

Non-condensing models tend to use slightly more power than a condensing unit, but both of them do not require that much power.

Non-condensing units have a faster healing time, and typically have a maximum flow rate of 2.5 gallons per minute (GPM). Condensing units tend to take slightly longer to heat the water as they work to condense the steam from your home’s hot water exhaust, and they typically have a maximum flow rate of 2.0 GPM.

Environmental Friendly:

Condensing units are much more environmentally friendly, as they can be powered using renewable energy sources. Non-condensing units need to use standard electrical power which is not always considered ‘green’ for the environment.


Non-condensing units are slightly more space-efficient than condensing models, but only by about an inch or two in height. This can be very helpful if your water heater is located in a small area of your home, but it is not something you should base your purchase decision on.

Uniform Temperature:

Condensing units tend to have more sudden temperature changes as the engine works to condense steam from hot water exhaust. This can result in slightly colder showers at first if you are used to taking an initial hot shower. Non-condensing units are slightly more uniform in terms of water temperature changes throughout your shower.

Ease of Installation:

Non-condensing units are typically much easier to install, as they can be mounted on any vertical or horizontal surface. Condensing models need to be installed at least 6″ away from the roofline due to the need for forced air cooling.


Non-condensing water heaters require yearly maintenance to ensure proper function and can burn out if they get too much dust trapped in the system. Condensing units will typically last for 10+ years without needing new parts or systems installed, but they must be inspected by a professional on


Condensing units are much safer than non-condensing models, as they will not overheat and cause problems such as leaks. If the unit freezes up or begins to malfunction for any reason, it will shut down until it can be repaired.

Non-condensing tankless water heaters have a higher chance of overheating and potentially causing a fire or other serious safety hazards. The unit must be inspected on a yearly basis to ensure that it is functioning properly and is not overheating.


Condensing units are much more resistant to corrosion, as they work with a closed system that is not exposed to hot water exhaust. Non-condensing models will typically have higher rates of corrosion due to the introduction of steam into the system.

About Zarmish Fakhar

Zarmish has been working as a freelance research writer for 5 years. She is a Zoologist and social media activist as well. She has worked for many reputable newspapers including Dawn. She is a valuable member of Aqua macho as her passion for clean water and eco-friendly products are booming day by day.

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