Selecting the Right Insulation Fibre Choice for the Domestic Boiler Market


As the US economy continues to gather momentum, housing experts are predicting that in excess of 1.3 million new homes will be built per month between now and 2024. While this is great news for housebuilders, it also directly affects domestic appliance manufacturers. One fact that is often overlooked is the impact that a good boiler can make on the energy efficiency and running cost of a house. Heating and cooling accounts for almost half of the energy expenditure of a typical US home and is therefore the largest energy expense for the majority of homes. When viewed in this light, the importance of a high performing boiler becomes undeniably clear. Central to the performance of a boiler is the choice of insulation that is used to minimise heat loss and therefore, the total amount of energy required to run the boiler. We can see a direct link between a number of important properties which dictate the energy saving potential of thermal insulation in boilers and reduced running costs for homeowners, but for appliance manufacturers in a cost-sensitive market, considerations around performance must be balanced against the need for a competitive price point.  

With a number of potential insulation options to choose from, Fiberglass and Refractory Ceramic Fiber (RCF) are some of the most widely used insulation types by appliance manufacturers. Developed and made available to the market in the 1950s, RCF features excellent thermal shock resistance and binder-free composition, making it well suited to domestic boiler applications. While RCF fibers have provided sufficient insulation in this market, issues around health and safety mean that it is often subject to regional legislation relating to the handling of the material. With this in mind, more and more boiler manufacturers are turning to Alkaline Earth Silicate (AES) wool solutions as a way of striking the optimal balance between its performance and the health and safety benefits it offers in the workplace.  

Energy Efficiency 

When it comes to insulating boilers, the thermal conductivity characteristics of the insulation material has a bearing on the amount of energy required to power the device. When thermal conductivity is comparatively lower, less heat is lost and overall energy efficiency is improved. Therefore it makes sense to go for materials with lower levels of thermal conductivity. Although the thermal conductivity properties of RCF are impressive, studies have shown that AES products can offer anywhere in the region of 15-20% lower thermal conductivity than RCF fibers, which can have a significant impact on performance. 

Design flexibility 

As consumers become increasingly energy conscious, this is reflected in the design of domestic boilers, which are being built to offer a more compact footprint than ever before. AES fibers offer superior design flexibility, due to their proven heat retention characteristics, allowing manufacturers to use less for the same result. When designers and manufacturers are targeting a specific level of insulation, lower thermal conductivity per square inch means that the AES delivers the same level of insulation but with less space use. Similarly, where there is a set amount of space allocated for insulation, the improved thermal properties of AES result in better insulating performance over RCF alternatives. Either way, for homeowners, a more energy efficient boiler translates into reduced running costs, making it a shrewd investment over time. 

One of the main advantages of RCF is its availabiity in a range of formats including blanket, board and paper. The benefit of this is that it allows for the insulation of all the different areas of a boiler, each with its own particular sizes and geometries. Where one form of insulation might not be appropriate, it is likely that another one can be implemented. Used primarily on the four sides of the inner part of the combustion chamber insulation, the rigid characteristics of board provide effective thermal insulation and strength while the flexibility of paper insulation lends itself particularly well to intricacies of the chamber casing.  AES is also available in all of the same formats as RCF, making it well suited to the various design challenges encountered by manufacturers of domestic boilers. 


Shrinkage of thermal insulation fibers is an issue for manufacturers of boilers, in that it can produce hot spots which allow heat to escape, reducing the efficiency of the boiler over time. This also reduces the energy savings for the homeowner. The rate at which shrinkage occurs in thermal insulation fibers, when exposed to sustained high temperatures, depends on how they respond when approaching their classification temperatures. It is beyond this point that permanent linear and thickness shrinkage can happen. Lower levels of linear shrinkage correlates with greater long term stability and performance. In actual fact, the linear shrinkage rates for AES and RCF are fairly similar at the typical operating temperatures of domestic boilers.  However, it is as you progress into the 1,000 -1,500 ºF temperature range, as seen in many industrial applications, that the difference in shrinkage rates between the two materials becomes clear, with AES coming out the more favourable of the two.

Bio persistence 

With the perennial issue of safety, it is also essential to strike a balance between the performance of insulation and potential hazards to human health. Typically, this is measured in terms of biopersistence, which is the ability of fiber to resist removal from the lungs by natural mechanisms. Because of the degree of human intervention in the manufacturing and assembly process, manufacturers of boilers need to be aware of the applicable regulations and how these might influence the choice of insulation fiber. Regulations vary between geographical markets, therefore it is important to have an awareness of the legal requirements of each market and how this might influence the choice of insulation fiber material. 

For instance, many boiler manufacturers have transitioned away from RCF because of EU regulations in the European market. Studies have shown that RCF fibers have a substantially higher level of biopersistence compared to standard grade AES fibers, with a half life of 300 compared to less than 40, respectively. Because of the high biopersistence properties of RCF, AES is a favourable alternative for manufacturers.  As a result, AES fibers are exempt from many regulatory workplace guidelines covering the handling and disposal of materials. 

As demand increases for boilers which are more energy-efficient, compact and sustainable than ever before, insulation will continue to play an important role within the domestic boiler market. AES insulation fibers are ideally suited for this application on the basis that they demonstrate similar levels of linear shrinkage to RCF, giving boiler manufacturers and homeowners alike the confidence that performance will remain constant over the projected lifespan of the boiler. Furthermore, AES offers the same level of design flexibility and versatility for manufacturers, who can also opt for AES as a way of ensuring exemption from applicable legislation, on account of its significantly lower levels of bio-persistence. However, the significantly improved thermal characteristics of AES over RCF results in better performance, improved energy efficiency, as well as a reduction in the quantity of insulation that is needed, potentially making a huge difference for manufacturers in an already price sensitive market.   

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Morgan Advanced Materials,
Morgan Thermal Ceramics,