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Condensing water heaters

Condensing water heaters

Multiple heat exchange technology is utilised to transfer maximum energy from combustion to the water being heated.

Condensing water heaters are available in multiple forms, condensing variants of continuous flow and direct storage are widespread. The fundamental differences between condensing and non-condensing are summarised here.

How do condensing water heaters work

When gas burns in a conventional non condensing water heater, the heat generated is available in two forms:

• Around 89% of it is 'sensible' heat, i.e. it can be transferred through the water heater heat exchanger to the system water. Typically conventional water heaters are limited to 80%-85% efficiency to ensure that condensate does not occur and corrode the inside components.

• The balance of 11% is 'latent' heat, i.e. Water vapour discharged through the flue Condensing water heaters take advantage of additional efficiency from their ability to pass most of the latent heat into the heating system. A non-condensing water heater would have an efficiency of around 81% to 84%, A condensing water heater will give between 103% to 107% efficiency as the latent heat is captured and flue losses are smaller.

Water heaters can only condense when the flue gases within the appliance are at their 'dew point' so to ensure continuous condensing operation the heat exchange surfaces and therefore the return water must be at low temperature.

Continuous flow condensing water heaters are one of the only truly condensing products. As the appliances almost always operate in condensing mode as the incoming water temperature is always low.

What are the pros and cons of continuous flow hot water systems?

AdvantagesDisadvantages
Higher efficiencies than non-condensing technologies Requirement for condensate draw off
Condensing continuous flow water heaters amongst the most energy efficient systems available in the European market Direct storage systems do not take full advantage of condensing technology due to hot water store proving wasteful with energy consumption
Condensing continuous flow water heaters operate in condensing mode constantly due to low incoming temperature Higher initial investment cost
Building regulations compliant
Subsidiaries and incentive available
Reduce CO2 emissions