How to use a mass stove.

Manual of:  How to use the mass stove.

A newly built mass stove must dry for minimum one month with all the doors, cleaning channels and dampers open- in a dry room. In other circumstances this period of time should be longer (if possible use a small fan heater in the fireplace for the last few days).
After that you start to dry it out with a fire, which also takes one month.
You begin to light it with ½ kg. of wood the first day.
The next day ½ kg. more (altogether 1 kg). In this way you increase the amount of wood with ½ kg per day until you have reached 14-17 kg of wood, which is the right amount of wood per fire in a mass stove. Read the fire manual below.
In this drying period water is being pulled out of the building material and water can even run out of the cleaning channels.
It is important that the drying is happening slowly because if too fast the water will “blow” itself out through the brick work.
Now the mass stove is once and for all “fired in “ and all the fireproof material is ready for the daily use.

Suggestions for heating the mass stove.

  • Pull out the damper fully before you light the fire.
  • Pull out the ash drawer 10-15 cm (there has to be enough air for the fire- which comes through the ash room). After 5-10 min. when the fire has really started you push back the ash drawer app. 3-6 cm. from the front, so that there is a clean burn, but not blazing.
  • The firewood, which has to be totally dry, is stacked like on the drawing below. The wood is chopped with a 10/10 cm. end. Light types of wood can be used like; pine, larch, fir, birch, alder among others, (need to dry under roof for minimum one year).
    Hardwoods like ; beech, elm, oak can also be used, (need to dry under roof for a minimum of two years).
    Wood pellets and the like cannot be used because there always has to be air between the wood pieces. If the air circulation is being hindered because of the wood being too tightly stacked it can create an explosion in the oven, because the gasses in such an event can’t get out and are accumulated in the oven.



We also recommend that you find a local timber/fire wood supplier who can supply the right wood (don’t necessarily trust that the wood is dry even if the supplier says so).


build up the fire.jpg

  • Feed 7-8 kg of firewood in the fireplace room as shown here at the drawing. Put paper and thin dry kindling on the top of the fire and light the fire here on top, this way the fire will reach a high temperature faster and the gasses in this phase will burn quicker- this way there will be less smoke from the chimney.
  • When the fire is half burnt. You fill the rest of the firewood in the fireplace room 6-9 kg. The total of the fire will be 1½-2 hours.
  • The fireplace, the doors and the handles on the doors get very hot during the fire, so we recommend to use fireplace gloves.
  • When the fire has burned completely down, push the damper fully in and close the ash drawer.
  • Now the oven will get warmer and warmer from this one fire.
  • The next fire is normally lit 22-24 hours after. If it gets colder you can increase the heat further by lighting a fire after minimum 4 hours with ex. 7-9 kg of wood. If it gets warmer in spring you can fire with the normal amount of 14-17 kg of wood every second or third day. In summer it is of course possible to burn smaller fires from time to time, in case of a cold and damp day.
  • It is a good idea to prepare the next fire minimum ten hour after the fire is finished, this way the wood will be completely dry for the next fire. Don’t do it earlier, the fireplace might be too hot – and you might make a big mistake – the firewood starts to burn at 275º C!
  • If there is a bake oven you can swep it clean (the ash can be swept into the gaps of the fireplace) and the oven is ready for use.
  • You have to get to know your bake oven- put your hand into the bake oven, count the seconds and when you feel it getting too hot it’s a hint that 8-14 seconds is good for baking white bread. A pizza needs it even hotter 6 seconds. We recommend using a roasting thermometer in the bread and meat. Most meat needs 68- 75 degrees C. Bread 95- 99 degrees C.
  • The idea is that the mass oven is lit every day.


The maintenance of the mass stove

  • We recommend that the stove is painted with silicate paint or plastered. This can only be done when the oven is completely dried out.
    Because of the big changes in temperature in the whole mass of stone we have purposely tried to avoid that the oven gets cracks by placing the fireproof “expansion joint” between the firebrick centre and the outer layer of brick. Even so, minor cracks can occur through some of the joints. This is not dangerous and those cracks can be fixed with a bit of paint or plaster.
  • Soot on the glass door can be removed easily with a little ash on a damp cloth or on a piece of rolled up newspaper. On the combined ovens where there is a fireplace and bake oven door you must expect that the glass in the bake oven door becomes black because of the massive difference in the heating and cooling on the bake oven glass. Therefore clean the bake oven glass regularly.
  • Make sure to empty the ash drawer so that the air intake works. If the ash gets up over the grate under the fireplace the grate can buckle and must be replaced. As previously mentioned if the primary air is blocked bad burning will follow.
  • Very important is to clean the flue channels at least once a year (do it when the stove is cold). Open the cleaning doors and move any ash. Do keep the stove clean inside all the time.
Fornyet Energi ApS, Øbrovej 9, 4295 Stenlille, Denmark
Phone: 57 80 45 22, E-mail:, 26108225
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