Periodical firing stove

This is the traditional stove that has heated saunas and baths for centuries. The more massive it is, the more heat it accumulates, but it also takes longer to heat up. The fire in such a stove is not separated from the load of stones, the flame and the hot products of combustion freely lick the stones and then enter the chimney. The stones heat up considerably when the stove is fired, the lower ones up to 1000°C and the upper ones up to 600°C (cherry colour). At these temperatures, the soot is completely burnt off and the stones remain clean. The stove is equipped with a flue damper and a steam vent with a door. When the sauna is heated, the steam door is closed and the damper is open, and the products of combustion escape freely through the chimney. When bathing, it is the other way round: the chimney is closed and the steam door is opened at intervals and water is poured over the stones. The splashes of water are instantly transformed into steam, which bursts out of the door and into the steam room in a powerful, hot gust. The door is then closed again. The stones in the stove stay closed inside the stove almost all the time, which means that the heat is retained for much longer and the sauna can be used for quite a long time.

Steam pouring into the Rimsa batch furnace.
 

Of course, the design of each specific stove may differ slightly from the one we have described.

Traditionally, hot water is produced in a boiler or in a metal tank which is built into the stove.

And here is how a Lithuanian sauna stove was described in the popular publication "Ūkininko patarėjas" (Farmer's Advisor) in the 1940s

"The simplest sauna stove can be made from stones picked outdoors. Although it is the cheapest, it is also the most imperfect. It needs a lot of wood, cools down quickly and lets out all the smoke and tar into the sauna, which, when let out through the door or windows, also lets out a lot of heat. The stove does not allow the porch to be warmed up, which makes it easy to get cold in winter. In addition, such an open stove can easily start a fire if it is used carelessly. A closed stove with a heating wall to warm the porch, a firebox and a chimney is a good stove that does not require much wood. Such a stove keeps the sauna heated for a long time and does not pollute the sauna air with smoke and slag.
It is best to build the sauna stove from fired clay bricks. The walls of the firebox should be one to three quarters of a brick thick and the walls of the stone compartment should be half a brick thick. The firebox of such a stove, to hold the stones at the top, may be covered in one of two ways: with iron saddles (which may be replaced by an old cast-iron machine wheel) or with brackets, with spaced intervals, made of non-combustible bricks. The bare, hot iron saddles must be plastered with non-combustible clay, wrapped with wire, to prevent them from sticking. The brick brackets should also be bricked with the same clay in place of the plain clay.

The sauna stove must be bricked at least 12 cm from the wall so that all sides of the stove can heat the sauna air. A heating wall is needed to heat the sauna. The chimney in the sauna shall be constructed in the same way as in other huts.

Prepared by Rimas Kavaliauskas