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Recover lost heat from the chimney

To improve the performance of an open fireplace, the first thing to do is to equip it with a heat recuperator, a system that captures some of the calories resulting from the burning of logs, to restore them to the environment. or to communicate them to the heat transfer fluid of the central heating circuit. The bulky devices proposed in the 1980s have given way to devices that today know how to forget their integration.

Air / air or air / water: real heaters

There are two types of equipment, which can be considered as real heating devices, especially when they are associated - directly or indirectly - with another heating device with automatic regulation:

  • the air recuperator takes advantage of the circulation of air necessary for a good combustion of wood to reserve some of it for the diffusion of heat;
  • the water recuperatormore complex to install, on the other hand brings the major advantages of a wider distribution of the captured heat and a thermal inertia which prolongs the efficiency of the fire when it declines and extinguishes.

Recover and diffuse hot air

The recuperators are used to distribute the heat recovered in the room where the fireplace is placed, but also in other rooms. Smoke evacuation specialists have taken a close interest in this problem and have developed devices that allow air to be diffused in almost every room in the house.
The simplest consist of a simple mechanized ventilation box. Hot air is drawn from the drains and / or hearth plate of the chimney. It is pulsed to neighboring rooms and distributed via a network of ducts and mouths.
The most sophisticated are inspired by VMC systems: the fresh air is drawn outside the house and directed to the drain where it heats up. A ventilation group with a flow rate of up to 500 m3/ h is distributed via a network of insulated ducts in the selected rooms. The operating cycle is automated by an adjustable thermostatic system, switching on or off the ventilation unit.

Operation of a simple air / air recuperator

Diagram of a simple air / air recuperator

Diagram of a simple air / air recuperator

In a simple air / air recuperator, the fresh air circulates from the teenager (see diagram on the left), the crawl space or the basement or the pyre, then will heat up going up in the cast iron heat exchanger at the hearth plate. The air thus heated is diffused into the ambient air by two mouths located on the hood of the chimney.

Diagram of hot air distribution

Distribution scheme

Distribution scheme

With such a device, the closed fireplace becomes a true complementary or main heating system depending on the power of the device, the size of the house and its number of rooms, and finally the quality of the insulation.

Transmission of recovered calories to the central heating system

By circulating water or to better express a "coolant" in tubings directly in contact with flames and burning logs, it can be directed directly to radiators (autonomous system) or to the boiler ( system in relief) to lighten its operation, and limit the use of fossil energy. In both cases, the system includes an expansion tank.

Operation of an air / water recuperator

Operation of an air / water recuperator

Recover lost heat from the chimney: heat

The air / water recuperator is in the form of tubing that lines the font of the fireplace hearth.

(photos / visuals: © Jøtul, except special mention)

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