Condensing Boilers - Seperating Fact From Fiction
A condensing boiler is a boiler that employs a more efficient method of extracting heat from combustible fuel than a traditional oil or gas fired boiler. A great deal of heat is wasted in a normal non-condensing gas or oil boiler in the form of hot flue gases that escape up the flue vent. This gas will be at a temperature of about 180C.
A condensing combi boiler is designed to permit these gases to rise as in a standard boiler but at the top the gases are redirected towards and cycled around a secondary heat exchanger, which draws heat from them, leaving them at a temperature of approximately 60C. Some condensing boilers even have dual heat exchangers, to extract even more heat from these waste gases.
This heat extraction and subsequent loss of temperature causes much of this gas to condense into water vapour, which then falls to the
bottom of the flue, where it is channelled either into a pipe leading to the household soil pipe or into a seperate drainage pipe that leads outside. A
circulating fan then blasts the remaining waste gas up the flue and away from the property.
Compared to standard non-condensing boilers which peak at around 75% efficiency, condensing boilers can be anywhere from 83% to 92% efficient, giving them a SEDBUK rating of B or A respectively, the highest possible.
What are the Pros of installing a condensing boiler?
- They use less fuel and can be anywhere from 15-30% more efficient than non-condensing boilers.
- In real terms, a family with a 400 annual fuel bill could expect to cut up to 60 per year off that total.
- Using a high efficiency or HE condensing boiler can lead to significant savings in your heating bill.
- They generate lower CO2 emissions than other types of boiler available.
- Each year a high efficiency condensing boiler could cut your carbon footprint by up to 1.7 tonnes.
- They are no more difficult to install than traditional non-condensing gas boilers, and come in a wider variety of sizes.
- Many models will comfortably fit into a kitchen cupboard.
- The majority of high efficiency condensing combi boilers makes no more noise than an air conditioning or PC fan.
What are the Cons of installing a condensing boiler?
- Some models have been known to generate as much noise on start-up as a jet engine taking off!
- They tend to be more expensive to buy than non-condensing models, anywhere from 100-300.
- They produce a visible plume of steam when they are operating.
- The condensing boiler flue terminal needs to be sited carefully to avoid creating a nuisance for neighbours.
- The process of condensation produces an acidic liquid that must be plumbed into a suitable waste pipe or drain.
- They need an advanced heating control system in place to operate at max efficiency.
- The home needs to be well insulated or the extra heat that a condenser boiler generates will be lost through the walls and ceiling.
- Central heating condensing boilers need an outdoor weather sensor (weather compensator) for maximum efficiency.
- If your condensing boiler is oversized for the task, it will be a lot less efficient that the proper size could have been.
- Your system will require a Power Flush to be carried out before the new boiler is installed.
- A chemical inhibitor such as the industry standard Fernox MB-1 will need to be added to the system.
Contrary to popular opinion based on information over 4 years out of date, condensing boilers are no less reliable than their non-condensing cousins. Early condensing oil boilers had rust problems caused by the acidic condensate but modern heat exchangers use non-iron metals to minimize or completely remove this possibility.
If your existing boiler is more than 15 years old, replacing it with a high efficiency condensing boiler could save you money, lower your
carbon footprint and contribute towards saving the environment. You may even qualify for the Government's Boiler Scrappage Scheme if you hurry!
As long as your home is sufficiently insulated, you have the central heating system fully and completely flushed before having your condensing boiler fitted by a Gas Safe Registered installer, there is no reason at all why your boiler should give you any problems.