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HVRs Anatomy Series: Anatomy of a condensing water heater

THERE is a certain inevitability about the use of condensing technology in the design and production of direct gas-fired water heaters. This follows legislation-driven moves in recent years towards condensing heating boilers.
HVRs Anatomy Series: Anatomy of a condensing water heater
One of the requirements for the most efficient operation of condensing boilers and water heaters is that return water temperature should be below 570C (dewpoint). In central heating systems this is often achieved by the over-sizing of heat emitters or by adopting specific controllers. The use of condensing technology within direct gas-fired water heaters is not quite as straightforward, as general industry design practice requires hot water to be stored at 600C in order to prevent legionella colonisation.

Lochinvar is one of the main suppliers of direct gas-fired water heaters in the UK, with its Knight and Charger products being among the first of this type of unit to be introduced to the market in 1976. These products are still popular today but recent additions of condensing gas-fired water heaters have taken efficiencies to even higher levels.

Turbo Charger

Turbo Charger employs many of the same design principles as the original Charger models but with the additional use of condensing technology. This product further improves operating efficiencies and consequently reduces fuel running costs and carbon emissions.

A fan assisted pre-mix burner is a standard feature and the triple-pass flue arrangement extracts otherwise wasted heat enabling Turbo Charger to achieve efficiencies of up to 109% net.
Other features include:-

· Room-sealed or Open-flued installation

· Low noise levels - 51dB

· Factory-fitted Correx - corrosion protection device

· Low NOx emissions


The second recent addition to the Lochinvar water heater family is the EcoForce+ with three models currently available. These units utilize a stainless steel heat exchanger and integral direct stainless steel storage vessel with interconnecting pipework and pumps fitted as standard. Using a patented cold water injection system, EcoForce Water Heaters ensure virtually continuous operation in condensing mode, achieving the highest possible efficiency for the end user.

EcoForce+ features also include:-

· Room-sealed or Open-flued installation;

· Optional anti-legionella function;

· Low NOx emissions;

Further EcoForce models are due for launch during 2007, with output ratings ranging from 80 to 180kW. These models will be wall-hung and supplied with separate direct storage vessel and primary pump, which will allow for various water heater and storage tank combinations.


For larger applications such as hotels, leisure centres and factories, Lochinvars' Copper-fin series, introduced in 1981 has been a popular choice among specifiers, contractors and end users. In 2003, the Intelli-fin range was launched and incorporates all of the well-established Copper-fin features but with the additional advantage of using condensing technology.

This achieves operating efficiencies of up to 108% net from a footprint of only 0.65m2. Other features include:

· 4 : 1 burner / air modulation

· Low NOx emissions

· Scale-free operation

· 5-year burner and heat exchanger warranty

THE major reason for the drive towards condensing boilers and water heaters has been to improve efficiency and reduce carbon
emissions. From a marketing viewpoint, manufacturers usually quote efficiency figures based upon Net CV and also under best conditions - hot water return temperatures of below 570C.

Part L2 of the 2006 revision to the Building Regulations and specifically the 2nd tier document (Heating Ventilation & Cooling Compliance guide) requests that water heater efficiency is calculated as follows:-

Water Heater Output / Gross Input = Gross Efficiency.

Where output is:

HW Recovery rate (l/s) x Specific heat capacity (4.18)
x Temperature rise required (eg 500C).


1. It is particularly important to calculate output based upon required temperature rise in order to obtain an accurate guide of operating efficiency.

2. Conversion factor from Net to Gross CV = 0.902
1 April 2007


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