gas condensing boiler

Permanently Condensing Boilers – A Perfect Energy Saving Solution

In times of rising fuel costs , we need to start thinking about utilising the technology now available.  Flexiheat UK are a firm believing in this. That is why we are at the forefront of energy saving technology.  We offer an ideal solution to achieving the goal of saving money and energy in the shape of our BK Permanently Condensing Boilers

BK Permanently condensing boilers

 Condensing Boilers – The History

Condensing boilers are water heaters fuelled by gas or oil. They achieve high efficiency (typically greater than 90% on the higher heating value) by condensing water vapour in the exhaust gases and so recovering its latent heat of vaporisation, which would otherwise have been wasted. The efficiency of a typical non-condensing boiler is around 75%,

Traditional condensing boilers, are really – SEMI CONDENSING BOILERS –As they are reliant on the return water being under 57°C for Gas and 47°C for Oil- Otherwise the physics of the heat transfer will not work !!!!

A Condensing Boiler

Permanently Condensing Boilers

The concept for BK Permanently Condensing Boiler is both ingenious and simple:  Fuel and flue gas temperatures are reduced to a minimum, ensuring the boiler operates in a condensing mode at all times.


BK Operation Animation



Permanently Condensing – How It Works -Step by Step 

  1. The flue gas is cooled down to approx. 70°C by the flue gas passes which are surrounded by the boiler water
  2. The water is heated up from at least 55°C to maximum 80°C, going upwards in a counter flow configuration
  3. The flue gas enters the secondary  heat exchanger made of plastic and cools down below its dew point temperature (48°C for Oil or 57 C for Gas )
  4. The flue gas leaves the system with less than 48°C (for heating oil), and it has an outlet temperature of about 20°C – 40°C at the end of the chimney
  5. The air ( combustion air ) which is taken from outside is already preheated in the chimney to approx. 30°C
  6. The burner combustion air is preheated to 50°C – 60°C, prior to entering the burner
  7. The preheated combustion air is lead to the burner via a hose and the cycle starts again


Permanently Condensing Boilers – Advantages

  • Heat Exchanger: The secondary heat exchanger had been engineered to resist the high sulphur content associated with burning oil. It is manufactured from A.B.S which is renowned for its resistance to acids.
  • Room Sealed: No additional combustion air is required
  • Fuel: The Kroll range of BK Permanently Condensing Boilers are available in both oil and gas
  • Environmentally Friendly: Because the exhaust flue gases are at such a low temperature, the polluting element of the gas can be neutralised in an environmentally friendly way
  • Efficient: The Kroll Condensing boilers have an efficiency of 106% for oil and 111% for gas

The Kroll condensing system does not need to meet the following additional requirements:

No  low boiler water temperature of 40/30 °C are necessary, therefore no danger of “legionella” when producing domestic hot water and no problems when heating  up the boiler itself –  i.e. Condensation forming in the combustion chamber

No increase of radiator sizes or the undesired subsequent installation of an  under floor heating system in order to be able to work inside the range of condensation..

No split heating / domestic hot water systems are required

* Also, due to the low flue gas temperatures, a low-cost chimney of plastic can be used. This avoids the expense associated with Stainless Steel flue systems

Energy Saving Comparison

For more information on our BK range, please click  here .  Alternatively, please give us a call on 01202 822222 and our dedicated sales team will be happy to offer advice and assistance or just contact us by mail by clicking here