We discuss heat sources for the systems in the United Kingdom in a series of interesting facts about boilers.
In its most fundamental form, this is simply a metal box that is surrounded by a fire. In fact, the first heating systems were just this, a metal box referred to as a back boiler, found within the fireplace of the lounge. Surprisingly, there are a few still out there in some older properties.
- A boiler is the appliance used to heat water for the purpose of supplying
a central heating system and hot water to taps. The term ‘boiler’ is
not ideal, however, because the water never actually boils inside the
appliance – if it did, there would be something seriously wrong.
Boilers today are fully automatic devices that turn up the heat
as necessary and, with the exception of solid fuel systems,
completely turn off when not required. The water is just heated
until the required temperature is achieved, as set by its built-in
thermostat, and then the heat source turns off. The fuels that
could be used for the boiler include:
CC solid fuel, including coal, wood and straw
Electric boilers are quite rare and so they fall beyond the scope of
this book. The remaining fuel types, however, have been used in
boilers for many years, and the design of the boiler has developed
into a very efficient appliance, unlike those of yesteryear.
Solid fuel has limitations in its design, and because these boilers
tend to be more labour-intensive – i.e. you need to load the fuel
and empty the ash – they are not very popular and account for
around only 0.5 per cent of all installations. Around 92 per cent
of installations use gas and the rest use oil.
Due to developments over the years, there are many different
boiler designs from many different manufacturers, with a neverending
list of models applicable to the particular designs. But
fundamentally they all fall into one of four basic types:
CC natural draught open-flued
CC forced draught open-flued (fan-assisted)
CC natural draught room-sealed
CC forced draught room-sealed (fan-assisted).
Essentially, these names relate to the method by which air is
supplied to the boiler:
CC Natural draught or forced draught indicates whether or not
the appliance has a fan incorporated to assist in the removal
of the combustion products to the outside.
CC Open-flued boilers take their air from within the room where
the boiler is located.
CC Room-sealed means that the air is taken into the boiler from
outside the building.
The boiler in your home will be of one of these. For
-If you have a back boiler situated behind a gas fire in the
living room, you have a natural draught open-flued boiler.
-If you have a large free-standing boiler in your kitchen, with
a flue pipe coming from the top, travelling into a chimney or
passing through a pipe to discharge up above the roof, again
this is likely to be a natural draught open-flued boiler.
Both of these types take their air from the room in which they
are installed, and this air is replaced via an air vent from the
If your boiler has a terminal fitting flush with the wall, it is most
likely to be a room-sealed appliance.
– If this terminal is quite large, it will be of the natural draught
– If it is smaller, say about 100 mm in diameter, it will be fan
These boilers do not take the air required for the combustion
process from the room, but directly from outside.
There are many variations of boiler design, where the location
of the fan or the route of the flue pipe – which may be vertically
through a roof or horizontally out through the wall – may vary,
but they all fall within one of the four basic types listed above.
In addition to the basic boiler designs, boilers are further
classified into four generic types:
CC non-condensing regular boiler
CC non-condensing combination boiler
CC condensing regular boiler
CC condensing combination boiler.
The differences between regular boilers and combination boilers
will be discussed in next post, but a new term is
used here: ‘condensing’. For more detailed information or to get boiler quotes – great value quotes from trusted local engineers visit quote a boiler.co.uk.