Cast iron boilers shouldn't be overlooked when considering replacing or upgrading commercial and industrial heating and hot water systems, says Pete Mills
The impressive efficiency levels of condensing boilers have been well documented to the point that, when replacing an older boiler system, energy managers and consultants often look no further than condensing technology for a solution. While condensing technology is the right choice for many applications, it is worth looking at all the options when specifying a new boiler; just to be sure the right technology has been selected for individual site requirements.

Today's cast iron boilers are well worth considering when upgrading a plant room. Most contemporary cast iron boilers have been designed as a result of thorough, optimised processes and when combined with the right controls, can often fulfil the needs of the end user just as well as a condensing model.

Regardless of the end result, assessing the needs of a new system should always remain a priority as no two sets of site requirements are ever the same.

Avoiding disruption

One of the main challenges installers face when carrying out heating installation work in larger buildings is replacing an existing system without causing widespread disruption to its occupants. When carrying out boiler replacements within older buildings in particular, the design of the old heating system is likely to have a significant bearing on the most suitable option for its replacement.

Having a constant temperature heating circuit with a Delta T of 82 flow and 71 return for example, will have led to the infrastructure including the boiler, radiators and pump to be sized accordingly. In such cases, the installation of a condensing boiler system may require alteration of a number of these associated components if it is to work in an optimum way. This is where the strengths of a cast iron boiler are enhanced.

The modern generation of cast iron boilers produce heat more efficiently to create greater outputs. Previously, the heat exchangers used within cast iron boilers often caused heat to be distributed unevenly, however more even distribution of heat is one of the reasons why the latest cast iron boilers can operate at seasonal efficiencies of up to 86.6 per cent - further enhancing the suitability of a modern cast iron boiler to replace its inefficient, older counterpart.

We have also found that cast iron boilers stand in a class of their own when it comes to oil-fired heating applications. Despite the development of condensing boiler technology over recent years, stringent fuel requirements often limit the compatibility of these boilers with oil. As a result, a cast iron boiler is often the best option. This is often the case in off-grid areas. However, there are a surprising number of buildings which rely on oil in more built-up urban areas, so high output cast iron boilers shouldn't be considered exclusively for off mains gas areas.

Another factor that can be overlooked is the compatibility of a new system with the existing infrastructure. From a technical perspective, replacement cast iron boilers have a low hydraulic resistance, which means they can be incorporated within the existing heating system with minimal changes to infrastructure.

This is a worthwhile consideration as it can minimise the cost incurred by adjustments to the infrastructure. However, the replacement of a cast iron boiler with a condensing system will inevitably mean some changes because condensing boilers require a condensate drainage outlet and a fully sealed flue system.

The key message here isn't that cast iron boilers offer an improvement on condensing boilers or vice-versa, but that each boiler replacement should be assessed individually. As with any heating system, however, controls have a large part to play in ensuring the efficiency of the heating system is maximised - and this applies as much to a cast iron boiler as it does a condensing boiler.

While much has been said about the efficiencies made possible by condensing boilers, a condensing system with ineffective controls will remain far less efficient than a cast iron boiler with a well-matched control system.

Given the number of options available for the installer working in today's commercial and industrial heating industry, specifying the best solution for replacement installations is always going to require careful scrutiny. However, despite the introduction of condensing boiler technology and renewable heating and hot water appliances, the long-established cast iron boiler still has an important part to play.

// The author is commercial technical operations manager at Bosch Thermotechnology //