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Room-sealed boilers

Room-sealed boilers

A boiler is said to be "sealed" when it operates independently of the air supply of the room in which it is installed. This principle is also known as "tight" or "forced flow"

Special review of room-sealed boilers: definition, operating principles and classification

Widespread in Europe, "room-sealed" boilers are of interest both in terms of the level of efficiency as well as the operational safety. Today most of the new systems installed in France are this type of boiler, generally in versions referred to as "high efficiency", but increasingly also in "condensing" systems whose performance is increasingly attracting interest.

Sealed-room boilers are classified according to types C1, C3, C4 and C5 - *


Smoke extraction system in an individual house

Smoke extraction in individual building

Smoke extraction system in a multi-family building

Smoke extraction in collective building

Operating principles

The sealed-room principle is also referred to as "tight" and "forced flow", as a motor allows ambient air to be drawn in and the combustion gases to be expelled.

Extraction of the boiler is known as "under pressure", as opposed to traditional systems with a natural draw, which are "in depression".

The air intake and smoke extraction are ensured by two flues, which are generally concentric: whilst the external flue guarantees the supply of air necessary for combustion, the internal flue is also used for smoke extraction.

The system can also comprise two separate flues pipes. This mode of installation allows for larger distances to be covered between the boiler and the outside in particular, as made necessary by the location.

The flue pipes can be assembled by simply sliding them together or by using joining collars. All feature sealed joints.

Please note

Type A systems are not designed to be connected to a flue pipe or a combustion product extraction system. The combustive air is released into the room of installation. The combustion products are expelled via the ventilation system in the room at the same time as the contaminated air. E.g.: gas stove.

Type B systems are designed to be connected to a flue pipe or a combustion product extraction system. The combustive air is released into the room of installation. E.g.: wall-mounted boiler, gas radiator.


*The sealed-room systems (C1, C3, C4, C5.) are classified according to:

  • - The configuration of the flue pipes supplying air and expelling smoke: concentric, dissociated or separate.
  • - The terminal's position: horizontal or vertical.
  • - The system: individual or collective.


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