The first of these - a heat resistance furnace. This feature is provided by the mass fraction of chromium in the product. It must not be less than 13%. Ask the seller about this criteria, so that after the furnace had no problems. Heat resistance allows the furnace with thin walls, which are needed to maximize your heating bath. Also, through such walls, the fuel burns slower.
The second criterion - the degree of heating stones and their number. Unlike Russian and Finnish saunas from others is the presence of the heater. This helps to clear the room of harmful microbes and promotes the appearance of pep. It is desirable that the heater was as many stones.
Experts recommend using these stones as porphyria, peridotite, basalt and Talkohlorit. Be careful, some stones have toxicity and heated, emit harmful contaminants that can poison the sauna visitor.
The third criterion is the size and scope of the firebox. The larger the volume of the furnace, the more its productivity. Dimensions of the firebox are responsible for the functionality and comfort of the furnace for a bath. Also a deep firebox will enable the owner does not spend time and energy on the chopping firewood. It is desirable to acquire a furnace in which the firebox has a tapering cross-section. It is necessary to form themselves from wood embers fell on the grate.
Material for the grate - the third criterion. Need for the grate to supply air to the lower layers of fuel, but not to remove the ash, as many people. Most good choice for the material of the grate - is cast, because it is only able to withstand excessively high temperatures. Is not capable of even steel.
Last, the fifth criterion - the mobility of the ash. Chamber in which the accumulated ash (ash pan) under the grate grate. Try to choose an ash box, which is in the shape of a box capable of advancing, so that you can quickly remove the ash when needed.