Space heating

Definition

Space heaters transmit their heat only to the surrounding space. This is usually done by heat radiation and partly by convection. They are typically used only occasionally for auxiliary heating. The following devices are among the most common space heaters in Europe: firewood space heater, tiled stoves and residential biomass cooker.

Biomass has also been used in the past for cooking and heating purposes. In developing countries, cooking and room heating is still often done with open fire sites. The resulting emissions endanger people and the environment. Advanced biomass space heaters have closed combustion chambers and carry the exhaust gases to the outside. Nowadays, biomass can be burned efficiently and with low emissions, using advanced combustion systems.

There are many different criteria for distinguishing between space heaters. In this article only space heaters, which are fired with biomass (log wood, pellets, wood chips), will be discussed.

Differentiation criteria

In the following, the differences between space heaters are discussed in more detail.

• Fuel – In biomass space heaters, usually log wood and pellets are used. Wood chips are only used for larger applications.
• Heat transfer medium – If the heat transfer medium is air, it is a stove and if it is water, it is a boiler .   Both can be designed as space heating units, but stoves are more common .
• Installation type – Space heaters can be manufactured industrially or assembled on site, like a tiled stove.
• Storage mass – This is the structural storage capacity of the space heater by chamotte or soapstone etc. It shows how much heat the stove can store. The storage mass of the space heater can be low to medium or high. A high storage mass is known as a storage heating stove.
• Feeding technology – The space heater can be fed either manually or automatically. Log wood is normally added by hand and pellets are often added automatically. There are different ways to move pellets into the combustion chamber.
• Operating time – The operating time does not mean the lengths of the heat output, but the duration of the ignition and recharging itself. Therefore  typically firewood space heaters and  residential biomass cookers have a long operating time, while a tiled stove has a short operating time. A tiled stove usually takes about an hour to ignite and the heat output lasts up to 12 hours.
• Heat transfer – The heat transfer can occur via radiation or convection.
• Combustion chamber – The combustion chamber can be made of metal or ceramic. There are also ceramic combustion chambers with a restriction for the secondary air supply. For combustion chambers made of metal, there are versions with and without a protection plate.
• Draught conditions – The draught can be naturally or evoked by a draught fan.
• Grate – There are space heaters with and without grates. Also the position of the grate can vary. In the case of flat firing systems, the typically fuel quantity is 2-5kg, whereas in the case of fill firing systems, far more fuel is common.
• Combustion principles – There are four different types: updraft combustion with grate, updraft combustion without grate, vertical downdraft furnace and lateral downdraft furnace

Types of space heaters (biomass)

According to the amount of differentiation criteria, there are a lots of different types of space heaters. In the following there is a short overview.

• Open fireplace – The combustion air is drawn directly from the room and the combustion quality is poor. The heating function is usually less important than the view of the open flame.
• Closed fireplace – Open fireplaces can be retrofitted to improve the combustion quality. Most of the heat is emitted by heat radiation.
• Firewood space heater – This stoves usually have a viewing window and a good combustion quality. The heat is emitted by radiation and convection.
• Storage heating stove – These stoves have a high storage mass to store the heat from the combustion. They have a high amount of radiant heat. An upper combustion principle is usually selected.
• Tiled stove – This kind of stove is assembled on site and requires expert knowledge for the installation. The amount of storage mass is high. The heat transfer is carried out by radiation and the operating time is short.
• Residential biomass cooker -  This type is used for heating and cooking. Various combustion principles are possible. They can also be designed as boilers.
• Space heating boilers – These units are also suitable for heating adjacent rooms. They are hydraulically connected to the heating system and have a heat exchanger. Space heating boilers provide also hot water. They are also known as extended space heaters.