Firewood – a smart and natural heat source

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Wood is a domestic, renewable fuel. Burning firewood does not accelerate climate change, since, as they grow, trees absorb the same amount of carbon dioxide from the atmosphere as they release when burned. In a good fireplace and with proper burning, the energy contained in wood can be converted cleanly into heat.

Economical additional heat

Wood-fired stoves are a traditional form of heating, but nowadays small homes tend to opt for it to complement other heating systems. The best result is achieved with massive, heat-retaining fireplaces whose structures release the stored heat evenly and for several hours. The energy efficiency of a heat-retaining fireplace is as high as 80–85%.

It is essential to burn 1 to 2 loads of firewood efficiently and cleanly

A suitably sized fireplace can meet more than one third of the building’s total heating needs. A heat-retaining fireplace requires less wood to heat up than a light fireplace, and correspondingly, consumes much less wood. A load for a heat-retaining fireplace is 3 to 5 kg, and only two loads are required. A third load can be added on the same day, if necessary. There is no need to burn more wood than the recommended amount, as it will no longer have any effect in terms of heating. Burning too much wood weakens the energy efficiency of the fireplace and the heat will be lost along with the flue gases. If several loads are burned one after the other, the warm fireplace structures cannot absorb the heat as well as cool structures – which means the lost flue gases are expelled from the flue at higher temperatures.

Warming up a heat-retaining fireplace is highly user-friendly, as it does not take up much time. Two loads will burn in roughly one hour.

No need to fear electricity outages!

In wintertime, homeowners may experience unfortunate breaks in their home heating if energy is interrupted due to high consumption. More and more people are installing heat-retaining fireplaces in their homes already during the building phase in order to safeguard their heat supply in all conditions and to lower their energy bill.

On nature’s terms

Environmental issues affect our day-to-day decisions, and the same holds true when it comes to choosing a fireplace. Wood that is combusted releases roughly the same amount of carbon dioxide as is released when it decays in the forest. Carbon dioxide eventually returns to the natural environment to serve as a building block for new growth. Uunisepät fireplaces are designed such that all combustion gases burn efficiently and thus no emissions arise.

Wood is therefore a clean, domestic and local energy source. There are no environmental risks related to transporting wood: it is not explosive and does not leach into groundwaters. The availability of wood is not affected by energy crises or international conflicts.

Only dry, clean wood in the fireplace

  • Only dry and clean wood can be burned in the fireplace – no wet, painted, impregnated wood, and no garbage. Dry firewood makes a clacking sound when tapped together.
  • Wood dries best outside in the sun, with good air flow passing between the wood stacks. Be sure to stack the firewood on timber bearers so that it doesn’t touch the ground.
  • Transfer the wood to a woodshed before the autumn rains. If the wood stacks remain outside over winter, keep them covered.
  • It is a good idea to empty at least a few days’ worth of firewood into the firewood box or carrier at once. The wood will dry somewhat indoors, too.
  • The wood’s thermal value reflects how efficiently it heats. Of all Finnish tree species, birch is the densest and has the highest thermal values. One stacked cubic metre of dry birch corresponds to the energy content of 170 litres of light fuel oil.

Tips and instructions for heating the fireplace

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With these guidelines, you can’t go wrong when lighting a fire.

Commissioning a new fireplace

After the fireplace has been installed, it must be left to dry for one week, with the dampers and the doors left open. The first fire should be lit slowly.

The right amount of wood

A load for a heat-retaining fireplace is 3 to 5 kg, and only two loads are required. A third load can be added on the same day, if necessary. There is no need to burn more wood than the recommended amount, as it will no longer have any effect in terms of heating. You will get the best heating result by following the usage instructions.

Sufficient draught

Before lighting the firewood, make sure there is a sufficient draught in the chimney. Temporary draught problems in the fireplace are almost always related to the chimney. If necessary, test the draught by lighting a match or a piece of paper in the flue or the chimney-sweeping hatch. The draught may be worse during a low-pressure system or a rainy period. Low pressure in the house can also negatively affect the draught. When lighting the fireplace, the mechanical air ventilation system or the range hood should be turned off, and it may help to open a window.

Ash box and grate

Always keep the grate clean. Check the ash box before lighting the fire and empty it if necessary. Efficient burning requires that air can freely reach the firebox from under the grate. This will keep the grate in good shape for a long time. Ash should be removed regularly into a fire-safe receptacle.

Stacking firewood in the firebox

Fill the fireplace with firewood such that at least one third of the firepit’s space is free. Air must be able to pass between the wood. You can lay the firewood upright against the back wall of the firebox, or if you wish to reduce emissions even more, you can burn shorter logs and stack them horizontally. Use birch bark and wooden matches or a small amount of newspaper to light the fire. For the first load, use firewood measuring 8–10 cm in diameter; thereafter, the logs can be slightly larger, 10–16 cm in diameter.


Open the damper in the chimney. If there is an ignition damper in the fireplace, open it. Open the ash box 2 to 5 cm. Lay the tinder (birch bark, fire-starter cubes, newspaper) on the grate and stack the wood on top of it. A horizontal load is lit from the top of the stack. Close the fireplace doors once the fire is lit. Close the ignition damper. Make sure that the fireplace receives enough air and that the logs burn nicely. With the right ignition technique, more heat will be absorbed by the fireplace and fewer emissions will arise from the combusted wood.

Adding logs to the fire

You can add more logs when more than half of the wood has burned and small flames are clearly visible. It is recommended that logs be placed bark-side down. Leave at least one third of the fire box’s space free. Avoid poking the wood unnecessarily, as this interferes with the fire.

Emissions in check

Wood burning produces flue gases that mainly contain carbon dioxide, water and a varying amount of particulates. When the burning temperature is high enough, the wood is dry, the fireplace has good air flow and the fire is controlled, fewer emissions are generated. The majority of smoke from a clean fire is harmless water vapour. Smoke that turns white after the fire is lit is a good indication of a successful fire.

Let it burn!

Two efficient and evenly combusted loads burning for 1.5 to 2 hours is sufficient to achieve good warmth. When wood burns, it burns on the surface. So, for example, ten pieces of wood weighing half a kilo each will burn faster than two logs weighing 2.5 kilos each. The damper closes the flue so that the heat does not escape with the air flow and to keep the fireplace warm for as long as possible. The damper also prevents the cold chimney from acting as an intake air channel. In terms of knowing when to close the damper, it is important to follow the manufacturer’s instructions.

Closing the dampers

The dampers must be closed at the right time. The smoke-control dampers are closed only once the last embers have burned out completely.

Make sure your chimney is clean

Property owners are responsible for having their chimneys swept, i.e. cleaned of soot. Chimney sweeping prolongs a fireplace’s useful life and improves its heat-emitting capacity. Chimney sweeps not only clean the fireplace, they also inspect the condition of the fireplace and the chimney.

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