The Differences Between Condensing and Non-Condensing Water Heaters 

As we approach the one-year mark since revisions to the approved Document L of Building Regulations were introduced, we’ve seen a significant step towards more energy-efficient domestic water heating in commercial buildings.  This change is the result of the installation of direct oil-fired or non-condensing water heaters being phased out and replaced by condensing water heaters.  While condensing water heaters aren’t new on the scene, the latest regulations have thrust their benefits into the spotlight.

Energy saving requirements

Since June 15th, 2022, direct-fired water heaters must have a minimum heat generator seasonal efficiency of 91% GCV (gross calorific value) for natural gas and 92% for LPG (liquefied petroleum gas). For indirect water heaters, the minimum heat generator seasonal efficiency is set at 91% for both natural gas and LPG. However, it is worth noting that the ‘seasonal efficiency’ for direct-fired products is measured according to the product standard that it has been manufactured to.  For most dedicated water heaters with storage this is most likely to be BS EN 89 and is referred to within this standard simply as ‘efficiency’.

These tighter standards apply to both existing and newly constructed non-domestic building stock and effectively eliminate the possibility of replacing non-condensing water heaters with like-for-like models, exceptional circumstances permitting.  Here, where condensing water heater replacement is deemed not suitable or practical by the Building Control Body, a minimum seasonal efficiency of 80% for gas, or 79% for LPG may be used.

Condensing vs non-condensing technology

So, let’s start by looking at the basic technology. A gas-fired water heater creates two types of heat, i.e., sensible heat and latent heat. Sensible heat refers to the heat transferred through the water heat exchanger to system water, whereas latent heat refers to the water vapour discharged through the flue outlet. Whilst conventional non-condensing water heaters do not make use of this latent heat and lose energy, condensing water heaters capture it. This ultimately means less heat is lost through the flue. Furthermore, as the captured latent heat is used within the water heating process, more hot water is produced per unit of energy, offering a more efficient and cost-effective use of fuel.

The Benefits of Condensing Water Heaters

Condensing water heaters are significantly more energy efficient than non-condensing units.  This is an important point when it comes to reducing emission from existing buildings and lowering operational costs, particularly at a time of rising energy prices.

Furthermore, in line with the current ErP requirements which state that water heaters must operate under specific NOx (nitrate oxide) thresholds of 56 mg/kWh for a single appliance, condensing water heaters contribute fewer emissions to the environment, making them a more sustainable choice.  As part of the condensing process, waste gases from the combustion operation are used to recover heat, which is also incorporated into the water heating process. As a result, lower NOx levels leave the water heater through the flue.

Compared to non-condensing units, condensing water heaters also feature a more modern design and usually have better controls and functionality built into them.

ACV Watermaster Evo Condensing Water Heaters

The ACV WaterMaster Evo range of condensing water heaters exceeds the new efficiency thresholds for Part L compliance. However, what really sets it apart from other products is the innovative tank-in-tank technology, a large heat transfer surface area that allows downsizing of the burner power and storage capacity, saving room and energy without compromising performance. High performance is guaranteed thanks to a passive flue gas recovery unit which preheats the cold inlet as well as lower volume of hot water storage while maintaining a high-volume output.

From a safety point of view, this is an important factor.  As lower storage volume means less stratification and risk of hot and cold-water pockets forming, bacteria formation such as Legionella is prevented.

The WaterMaster Evo offers industry leading efficiency and performance for a product which is one of the most compact and light weight water heaters in its class on the market. All models are ErP-compliant, and models 70kW and below are water heating energy efficiency class A.

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