Condensing Boiler System Myth Busting

There are many reasons why engineers have been led to believe that condensing boilers do not fit a design application. Most of these reasons are inaccurate as condensing boilers can be used in most applications where a standard, non-condensing boiler can be used. Some of these reasons may have been valid for older, non-condensing boiler systems, but for condensing boilers, many of these concerns have been eliminated.


David Grassl, PE, Principal, Dynamic Consulting Engineers


Within the condensing boiler segment, there are a variety of technologies available. Some condensing boilers require more maintenance than others, or have specific piping, pumping, and flow requirements. High mass firetube condensing boilers have been developed to overcome many of these obstacles, and can be piped in a variety of systems with success. Therefore, it is important to understand each boilers’ operating requirements, as well as total cost of ownership, when making a boiler selection. 

Below are just three of the seven myths that are discussed in this paper:

Myth -- We Need to Maintain a 20°F System ΔT.  Older systems typically maintain a low ΔT in order to keep the hot water return temperature above condensing conditions. In condensing systems, temperature differentials of 30°F or higher can be designed to increase boiler efficiency by lowering the hot water return temperature back to the boiler. 

Myth -- Hot Water Reset Doesn't Work. Hot water reset is a simple control strategy that has been used for many years on hot water systems with a lot of success. With condensing boilers, the hot water reset functionality based on outside air is generally built in, making this a relatively low- or no-cost item to implement within the system. 

Myth -- Variable Flow Primary Systems are More Complex. In actuality, variable flow primary systems are simpler than primary secondary systems as variable flow primary systems only require one set of pumps to handle everything in the system. Also, there is no mixing due to two hydraulically separate pumping loops and less equipment is required, so there are fewer devices to control. In variable flow primary systems, there are three items that must be addressed for proper system operation.


Condensing boilers are not more difficult to design, install, or service compared to non-condensing boilers. In fact, the opposite is true for high-mass condensing boilers, which are generally more robust and require less attention. 

Discover More

{{ 'Education & Training' | limitTo: 50 }}

Cleaver-Brooks has a dedicated Training Department offering Web-Based Programs, Co-Sponsored Authorized Representative Regional Programs, Custom On-Site Programs at the customer’s facility, and programs held at Cleaver-Brooks facilities.

{{ 'Genuine Parts' | limitTo: 50 }}

Purchasing Cleaver-Brooks Genuine Parts is the best way to keep your boiler system operating at peak performance. Our parts are precision-engineered to fit your boiler, and they are rigorously tested for quality to ensure your boiler runs safely and reliably.

{{ 'Rental Solutions & Services' | limitTo: 50 }}

Our rental solutions provide for: capacity increases, peak demand, plant or steam outages, equipment shutdown due to inspection, retrofit or repair, and redundancy or disaster response contingency plan.