And science proves it

NunnaUuni is constantly developing its fireplaces . That is why we cooperate with universities and research institutes regularly. Impartial experts have verified the excellent durability and thermal properties of Mammutti soapstone and the effects of the Golden Fire burning method on the significant reduction of particle emissions.

You can find more detailed information about the studies below.

A heat-resistant soapstone fire chamber stores a lot of heat

The hotter you can heat the fire chamber material, the more energy its mass can store. The volume of heat (kWh) stored per cubic metre of soapstone (m) at different temperatures. (Source: adapted from VTT-S-05448-06)






Even heat release







In addition to the CE test, the heat-storing NunnaUuni fireplaces are tested with the SAA 142/222 method. It measures the evenness and output of heat released by the fireplace into the room. The nominal heat output of the example fireplace is 2.3 kW, and the duration of its even heat release period is approximately seven hours. The nominal heat output indicates the output of heat from the heat-storing fireplace into the room. It helps you to select the NunnaUuni fireplace that best suits your heating needs.

NunnaUuni has gained top results in a demanding test for heat-storing fireplaces








* Particle measurements: Tampere University of Technology, Institute of Materials Science. Other figures: Fraunhofer Institut für Bauphysik.
** red. O2=13 % = the amount of oxygen in the smoke gases is 13%. The reduced measurement results are comparable.

The top results for NunnaUuni fireplaces have been gained in the SAA 142/222 and EN 15250 tests for heat-storing fireplaces, where all smoke gases generated during burning are exceptionally measured throughout the burning process, starting as soon as the wood ignites.

A summary of the material research results concerning Nunnanlahden Uuni Oy's MammuttiStone deposit:

Research report: Material study for the MammuttiStone deposit [pdf, 765 KB]

Heat-storing fireplaces and stoves have different CE markings

When comparing the test results from different fireplace manufacturers, you should take the fact that stoves and heat-storing fireplaces have different CE product classifications into account. This is because the thermal properties of stoves and heat-storing fireplaces differ greatly from each other.

CE EN 13240/Stoves
• The amount of wood burned during the preheating period is not taken into account at all in measuring emissions and calculating the efficiency.
• The test measures instantaneous thermal power (kW), not the usable thermal efficiency (kWh). The nominal heat output is the average heat output for this period.

CE EN 15250/Heat-storing fireplaces
• Emissions are measured for the whole burning period as soon as the wood ignites.
• The test determines the amount of usable thermal energy during one heating (kWh): the heat release time and the actual efficiency.

A heat-storing NunnaUuni fireplace is a truly environmentally-friendly and sustainable choice.

NunnaUuni always markets stove-tested products as stoves. However, there are also stove-tested products on the market that are marketed as interior decoration fireplaces or semi-storing fireplaces. You should be careful when selecting a fireplace!

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