Fireplace and firewood

Wood as a fuel is a natural source of energy. When burned properly, it burns almost smokelessly and produces a small amount of ash. Quite a lot of water is bound in the fuel, e.g. a freshly felled tree can contain up to 50% water.
The ash content of wood is less than 0.8 %, in low-quality brown coal it can be up to 40 %.

During combustion, the fuel releases energy bound in its mass. We measure all kinds of energy, regardless of its form, in units called Joules.

The heat input per unit time is called heat output. The unit of each form of power is the Watt. The relationship between power and energy is 1 Watt = 1 Joule/sec, respectively. 1 Ws = 1 Joule.
In practice, we use multiples of these units: 1 kW = 1 000 W, 1 kWh = 3 600 kJ, respectively. 860 kcal.
We get the best idea of the energy of a fuel if we give it in the commonly used unit kWh. 1 kWh = 3 600 kJ, resp. 3,6 MJ
To illustrate, the energy of 1 kg of dry firewood of 15 MJ expressed in kWh is: 15 000 / 3 600 = 4.2 kWh.

Recall that the power of an average vacuum cleaner is 1 kW, this means that the energy hidden in 1kg of wood can power the vacuum cleaner for more than 4 hours!

Fire is a chemical reaction where the combustible components of the fuel combine rapidly with oxygen in the air. A sufficiently high temperature and sufficient oxygen are prerequisites for combustion. The result of combustion is the heat released and gaseous waste in the form of carbon oxides, nitrogen, sulphur and water vapour.
Local heating in the transitional period, before and after winter, will easily allow to temper the family house. The advantage of combining central heating with local heating is also the bridging of a possible gas supply failure, which is often heard about in the information media. The price of imported energy is high and will be for a long time to come.