How fireplaces work, smoke draft and what are the main types

The fireplace or fireplace And the oldest instrument used for heating a home. It still represents one of the most used elements for the creation and management of the heating system today, with all the relevant evolutions. In this context, the operation of a fireplace is a mix of application of simple concepts fluid statics And fluid dynamics combined with geometric engineering of the elements making up the system as a whole. Basically, the difference in temperature between the air inside and outside the chimney generates a pressure that pushes the fumes towards the chimney, where they rise again: this is the so-called draft. Let’s see together what are the recurring types of fireplaces used and what is meant when it comes to fireplace effect.

How a fireplace is made

The fireplace It is made up of several elements which together perform the task of guaranteeing the heating of the environments involved. In fact, in addition to the actual space that outlines the fireplace (where the wood, or in general the combustible material), we also find the chimney fluei.e. a hollow element, hidden in the building envelope, which connects the space where combustion takes place with the outside, i.e. a high point of the house: the chimney accompanies the fumes produced by combustion towards the outsidethrough a game of fluid balance which takes the name of fireplace effect.

What draft is and how it works: the chimney effect

The natural removal of fumes due to combustion can be understood by applying the laws of fluid staticsor more simply law of communicating vessels. In essence, the removal of exhaust fumes towards the outside (precisely along the flue) occurs thanks to a pressure difference between fluids at different temperatures: the hotter air reduces its density and is therefore pushed by the air less hot, external to the chimney, which has a higher density.

Exists an imaginary wall of separation between the area outside the fireplace and the internal one: in the external area we find the cold air, which exerts pressure (i.e. pushes inwards) on the hot air. On the other hand, the hot air inside the fireplace (on the other side of this imaginary wall) he doesn’t have the strength to counteract this push and therefore it cannot do anything other than suffer the push and move away towards areas of lower pressure, i.e. along the flue. This thrust force is usually called draft and actually represents the way in which exhaust fumes are removed from the home. This physical phenomenon is called fireplace effect!

Malfunctions in this sense may exist, this obviously depends on various factors. Excluding errors in the design of the fireplace and flue spaces, these problems can be encountered, for example, following exhaust section reductions due to the creation of accumulations of solid material produced during combustion and carried along by the fume flow. The reduction of the section useful for the flow of fumes causes a resistance to motion along the canal that can compromise the static balance of pressures generated at the chimney-environment interface. The result is one incorrect dissipation of fumeswhich can therefore accumulate undesirably in other environments.

The difference between open and closed fireplaces

Commonly, we are dealing with fireplaces traditional (also called open fireplaces) or thermo fireplaces (also called closed fireplaces). What changes between the two types?

The operating mechanism is the same, but in reality the heating of the rooms occurs in completely different ways: in the first case (open fireplaces), the heating occurs completely by irradiation, and in fact the area benefited from this increase in temperatures is usually very limited. In the second case (heated fireplaces), as well as by radiation, the heating is spread across different environments through a system that works in series with the fireplace. In this case, the fireplace itself is separated from the room by a glass element. The additional system to the fireplace it can be both air and water: in the first case there are some vents which deliver hot air into the rooms (not just around the fireplace). In the second case, a serpentine serves as heat exchanger and allows the circulation of hot water in the system (for example in radiators).