Increasing energy costs and environmental responsibilities are just some of the factors contributing to a surge in demand for efficient water heating systems.

Condensing technology, used in instantaneous systems – also known as continuous flow–systems, represents the most up-to-date method of energy-efficient gas-fired water heating. Bosch Hot Water National Commercial Manager James Smith says “The condensing process can deliver thermal efficiency of over 94 per cent, which can translate to significant energy savings.”

New condensing system models are available – some with 6-plus star energy ratings – which can deliver energy savings of up to 16 per cent as compared to standard continuous flow units.

Condensing systems have powerful heat exchangers that capture much more of the heat from the fuel source than traditional models. Instead of wasting the heat in the exhaust gases that are expelled through the flue, the heat is captured and utilised in the water heating process.

How does it work?

In a conventional continuous flow system, there is one heat exchanger. The water passes through the exchanger and is heated by a series of burners. Exhaust gases then exit the flue, unused, at temperatures of approximately 200–250 degrees Celsius.

In a condensing system, there are two heat exchangers – one for primary heating and one for secondary heating. Water first passes through the secondary stainless steel heat exchanger, which captures residual heat from exhaust gases. The exhaust gases cool and condense as they transfer their heat to the incoming water. The warmed water then enters a primary copper heat exchanger.

Acidic condensate is a byproduct of this process. As such, condensing systems contain an in-built neutraliser to ensure that condensate is pH-neutral upon its release.

Condensing the costs

Another benefit is the reduced exhaust gas temperature at the flue of just 50 degrees Celsius. This means that low-cost polypropylene can be used for ducting, reducing installation time and costs.

Being continuous flow, a condensing system works on-demand, only heating water when needed. In contrast, storage water heaters store and heat water 24/7, resulting in higher operating costs. And while storage units have a limited supply of hot water, continuous flow systems provide an endless supply.

Where are they used?

Condensing technology systems are suitable for both domestic and commercial use.

Residential installations of condensing units are growing in popularity as the technology becomes more recognised within the home building sector.

Purpose-built commercial systems can cater to demand for large volumes of hot water, such as in business or industry buildings, or in homes with three or more bathrooms. By switching to new condensing technology, and with proper system selection and installation, commercial facilities can reduce their water heating energy requirements by up to 40 per cent.

Mr Smith says “A true commercial unit can be installed internally or externally and has the capacity to operate for up to 16 to 20 hours per day.”

“Installation can be as a single unit, manifolded or in combination with storage.”

Over time, heavy workloads in commercial use do have the potential to cause corrosion, for example, to the copper heat exchanger or internal parts. It is therefore important to ensure the condensing system chosen has commercial-grade components throughout, including thick copper piping to prevent corrosion and deterioration and a heavy duty resin-coated printed circuit board for durability.

Warranty periods should also be checked and compared before selecting a condensing system.

Globally popular

Condensing systems are largely replacing conventional designs in Europe and increasingly, in North America.

All new gas central heating systems fitted in England and Wales must be high-efficiency condensing systems, unless there are exceptional circumstances. In the United States, there is a federal tax rebate for their installation, plus additional rebates in some states.

As energy efficiency becomes a key global concern, condensing gas hot water systems provide a cost-effective, viable alternative for both domestic and commercial water heating.