A convection box, or heat chamber of a fireplace insert, is one of the fireplace components responsible for distributing heat effectively around the room. It is a special structure that surrounds the insert and controls the flow of air.
What is a convection box and why is it needed?
The basic operating principle of a fireplace convection box is convection — the transfer of heat through the movement of air. When firewood burns in the fireplace, it releases heat that warms the surrounding air. This heated air rises and gathers in the convection box. The box has special openings (ventilation grilles) through which the heated air leaves and spreads through the room.
A convection box can have different shapes and sizes depending on the specific fireplace model. Using it allows heat to be distributed evenly throughout the space: it helps avoid overheating individual zones near the fireplace and keeps the temperature comfortable in the whole room. In addition, the convection box can be used to heat air in other rooms via ventilation ducts.
Requirements for building the heat chamber (convection box)
To prevent overheating that could disrupt the normal operation of the fireplace, a ventilation system for the box and the cladding (the internal space of the fireplace) must be provided using ventilation grilles.
For the heat chamber structure it is recommended to use calcium silicate boards or other heat-resistant boards. The inside of the heat chamber may be lined with mineral wool with the aluminium facing turned towards the inside of the fireplace, or with calcium silicate boards or other refractory materials.
! ATTENTION ! Only non-combustible, purpose-made materials may be used to build the heat chamber.
At a distance of at least 30 cm, and preferably 40 cm from the ceiling, install a horizontal deflector that directs the heat from the insert towards the grilles located below that same deflector.
Why is a larger gap from the ceiling better?
It is precisely under the ceiling of the box that the hottest air collects, and it needs to escape freely through the grilles rather than press against the slab. The larger the gap between the deflector and the ceiling, the easier it is for the hot air to move and the lower the risk of overheating the ceiling itself and the finish above the fireplace. So 30 cm is the minimum that still works, while 40 cm is the margin at which the system behaves noticeably more calmly. That is exactly why the grille cooling the decompression chamber is recommended about 40 cm from the ceiling.
The casing (convection box) must be built so that the fireplace and the connector (the duct linking the fireplace to the chimney) can be cleaned. Remember that the elbow of the connector must also be accessible for cleaning. Ensuring air exchange inside the insert casing is mandatory. The casing should be as large as possible so that it does not accumulate too much heat inside the heat chamber.
How far from the insert should the chamber walls be?
It is recommended to place the walls of the heat chamber at a distance of at least 10 cm from the body of the fireplace insert. Between the door frame and the wall of the heat chamber it is recommended to leave a technological gap of 5 – 10 mm.
! ATTENTION ! Operating a fireplace insert without a heat chamber may damage the appliance.
Which SAVEN grilles are available?
A convection box does not work without grilles: it is through them that cold air enters the heat chamber from below and the heated air leaves into the room at the top. The SAVEN catalogue has four lines of fireplace ventilation grilles, differing in shape and installation method:
- CLASSIC — classic ventilation grilles, the familiar look for most fireplace surrounds;
- LOFT — straight grilles in the modern loft style, the widest choice of sizes;
- LOFT ANGLE — corner loft grilles, designed for corner fireplaces;
- HIDE — concealed grilles, almost invisible in the surround.
All the lines are gathered in the fireplace grilles section. For current sizes, colours, availability and prices please check with a manager or a representative in your region — the set of grilles is selected individually for the specific box and the output of the insert.
The box itself is built around specific equipment, so it is worth choosing the insert first: straight steel inserts, corner steel inserts, inserts with a guillotine door or fireplace cassettes. Do not forget the chimneys either.
We emphasise! Installation of the fireplace insert and its convection box must be carried out only by a qualified specialist in accordance with the applicable standards. That is the guarantee of safe and correct operation of the appliance, and it lets you protect yourself and your family while keeping your home a safe and comfortable place.