How does How Boiler Refractory Work?

Cleaver Brooks Boiler Door Refractory

Refractory is One of the Most Important Components Within a Boiler

Boiler refractory plays a critical role inside for proper and efficient operations. Gas and oil-fired burners can produce temperatures upwards of 3000° F +/-. inside the furnaces or fireside of the boiler. The heating surface of a boiler depends on the water inside for thermal protection and structural retention whereas areas not protected by the water-wall rely on refractory. One exception here is in the throat tile area of certain furnaces. The refractory around the burner head actually protects the flame from being cooled too rapidly (from heat transfer) along with creating the proper flame shape and velocity. 

Boiler refractory is heat-resistant material that lines the high-temperature areas of the furnace. Refractory usually consists of castables, bricks, ceramic wools or fibers, and even plastics made from various fireproof compounds. Typical to most industrial and commercial boiler applications is the use of firebricks, castables and, cerewool or fibers. 

What is often misrepresented is the important correlation that a boiler’s refractory has to its efficiency and reliability. Bad or deteriorating refractory eventually leads to a whole host of other problems. 

Over time the refractory will begin to degrade. This is especially true in certain areas like the rear wall that can see some of the highest temperatures. As the refractory begins to fail its effectiveness begins to lessen. Common reasons that cause refractory failure can be due to thermal shock, over-firing of the boiler or excessive temperatures, improperly installed or cured refractory, or wrong material selection. 

When castable refractory is not cured correctly, moisture can become entrapped inside and when fired it will flash to steam. As the steam expands it will blow out the refractory and cause voids and recesses inside critical areas that require thermal protection. 

The good news is that refractory if installed correctly requires only minimal maintenance. Quarterly to annual inspections based on operational needs are the first step in keeping refractory at its best. Secondly,  ALWAYS refer to the boiler manufacturer’s recommendations on refractory inspection frequencies, procedures, and any other specifications.

At a minimum, a fireside open clean and close should be performed annually by a qualified boiler service provider. Trained boiler repair technicians can quickly identify areas of refractory that may be failing. Some operations may require more frequent inspections so plan accordingly. 

Certain boilers require an annual wash coat to the rear door or a target wall of the boiler. This is the area that sees the greatest temperatures and a properly applied wash coat with the proper material fills in small cracks that are common to this area. This practice will ensure that the areas subject to common refractory failure are in top shape. 

Getting your boiler tuned regularly plays a critical role in keeping refractory intact. Improper combustion only leads to other problems like flame impingements, over-firing or sooting that can begin prematurely degrading the boilers refractory.  




The rear door refractory of a dry-back boiler is a common failure point. These areas can fail and leave plants offline with little to no warning. A common practice is to utilize what we refer to as a change-out door. Much like the process of a core part at an auto parts store, an exact match that is cured and ready to install is exchanged versus the extended time of curing on site. Many plants can have a dry back boiler door swapped and installed the same day considering door availability

All new refractories will still require some installed curring to ensure that the new material is slowly brought up to operating temperature. The improper firing of properly fired new materials will still result in refractory failure. This is again a reason to ensure that only qualified boiler service professionals are performing your facility’s refractory work.

If your facility is in need of refractory inspections, repairs, burner tunes, or an open clean and close, contact Power Mechanical Inc. today. We have been servicing industrial and commercial grade boilers for over 36 years and know what it takes to keep your steam and hot water boilers performing their best. Call today to schedule your boiler service. 

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