How does a wood-burning fire combustion system work?

With a wood-burning fire, many people still think of the classic open fire. Although a classic fire looks cosy, there are some drawbacks to this design. An open fire has an output of only 10 to 15%, for a contemporary closed fire this is 70% and for certain stoves it is much higher. Moreover, a fireplace is considerably less safe. If you want to burn wood responsibly and efficiently, it is much better to heat using a closed fire or stove. This is because a higher temperature is achieved in a closed fire or stove, which makes combustion more complete and efficient.

A brief explanation about combustion in a wood-burning fire or stove

Combustion, whether it is gas or wood, always requires oxygen. There is a distinction between open and closed combustion systems. Open combustion systems draw the required oxygen from the surrounding space. With closed combustion systems the oxygen is supplied from outside. A glass door in a fire or a wood-burning stove does not say anything about the combustion system used: a closed stove or fire can have either open or a closed combustion.

Open and closed combustion for wood-burning fires and stoves

In most cases, a wood-burning fire or stove has an open combustion system, even if the fire or stove is closed off with a door. The oxygen is drawn, through air vents, from the living area itself. Good ventilation is an important prerequisite for burning wood in a fire or stove that has an open combustion system.

The supply of oxygen in the air enables combustion to take place and the draught, the exhaustion of smoke through the chimney or the stove flue, is also maintained. For a wood-burning fire or stove, an open combustion system is the simplest and most common setup.

Closed combustion with a wood-burning fire or stove

Despite this, there are a number of situations where an open combustion system for a wood-burning fire or stove is not desirable or possible. The frequent use of an extractor hood in the same room, a mechanical ventilation system or a WTW system, makes open combustion complicated and even dangerous. When all windows and doors are closed, a vacuum can be created due to these installations. The vacuum interrupts the supply of oxygen to the fire or stove. As a result, you run the risk of the smoke coming back into the living area. Obviously, this can be taken care of by opening a window, but this will cause you to burn more than necessary. Moreover, this disturbs the well-balanced indoor climate in an energy-efficient home. In these cases, it is therefore better to equip the wood-burning stove with a closed combustion system. You do this by creating an external air supply to the stove, known as an outside air connection (EA).

Room Sealed appliances: especially for highly energy-efficient homes

A passive house is, among other things, fitted with optimal thermal insulation and good airtightness, making maximum use of the available heat. In this type of house, a ‘room sealed appliance’ is a suitable choice. These appliances are suitable for a closed combustion system, which draws the required air from outside.

Connecting to a closed combustion system does impose additional requirements on the outlet and supply. Ask an authorised dealer about the possibilities for your specific situation.

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