Walltherm® - Zebrú
The first water heating wood gasification stove for the livingroom!
The Walltherm® is the first ever stove to combine the characteristics of a traditional stove with the technical attributes and efficiency of a reverse combustion log gasification boiler.
The stove has a very economical and ecological way to burn the wood because of the gasification process. This means it uses less wood than most other stoves but provides even more power. It achieves very low emissions (only 24mg) and an unparalleled efficiency of 93%.
Through its unique double windows, the Walltherm® gives you an extraordinary sight of two flames. In the upper combustion chamber you can admire a cosy wood fire while the lower combustion chamber shows a spectacular gasification flame burning in reverse.
The reverse flame is not only beautiful to see, but it´s also very hot (over 800°C). The extremely hot exhaust gases exit the stove through the internal heat exchanger which is designed to absorb the highest amount of heat possible.
The temperature of the outgoing exhaust gases on top of the stove is only about 130°C - 170°C depending on the chimney draft.
In total, the 14,9kW of the stove can be used to heat a normal house of up to 150m² including the domestic hot water.
With the radiant heat of about 4,5kW, the Walltherm® supplies a room of up to 50m².
Because of the high power output of the stove, we recommend connecting a storage tank with 1000 liters or more.
We can offer the Zebrú model in black and grey color.
References: Walltherm® wood boiler Zebrù
Efficiency: 93 %
- Energy efficiency class: A+
- Power: 14,9 kW
- How the heat is divided: 70% to the water, 30% radiant heat
- Fine particles: 24 mg/Nm³
- Combustion air connection from bottom: ø125 mm
- Combustion air connection from behind: ø125 mm
- Operating pressure: 2 bar
- Chimney draft 12 Pa - 15 Pa / max. 20 Pa
- Weight: ~ 275 kg
- Water contenc: 16 lt
- Combustion chamber size: 55 lt
- Chimney connection: ø150 mm
- Exhaust stream: 38,5 kg/h
- Exhaus gas temperature: ~ 130-170 °C
- Exhaus gas temperature (lighting phase): ca. 250 - 300 °C
- Fuel: dry wood (under 20% humidity)
- Lenght: up to 35cm
Warranty: 5 years on the body (wear parts excluded), 2 years on fittings and electrical components
Recommended for the Walltherm:
The optionally accessory WAL03:
Based on a digital solar thermal controller, this special version called WAL03 can also be used to operate the Walltherm stoves. The display shows you relevant values like exhaust gas temperature and the water temperature in the stove and in the storage tank. Furthermore it can sound an alarm if the exhaust gas temperature rises above a certain value, to remind the user to close the exhaust fume flap of the stove.
NEW: the controller WAL03 closes automatically the electric air inlet flap, if the water temperature isn't high enough. This function prevent a cooling of the not working stove due to the cold air circulation from the outside is stopped.
Frequently asked questions
The Walltherm works with the natural draft of the chimney, the draft is therefore very important. It must not be less than 12Pa and 15Pa would be great. Your sweep can measure the draft and confirm the values.
A chimney of 6m or more of vertical lenght and a (round) diamenter of 150-200mm is usually perfectly working. The chimney must be insulated! Horizontal smoke pipes reduce the draft so avoid them if possible. Connecting the stove with a 45° or 60° angle to the chimney is better than 90°.
No. While heating up the Walltherm, the fume flap is opened and the fume can exit the stove with relatively high temperatures of more than 300°C. This will preheat the chimney and the humidity dries out. Only after the chimney is hot, the gasification process is started. The exhaust temperature drops to 130-170°C but because of the clean burning, chimney sooting will not occur.
Wood should be stored in a dry place for at least 2 years before burning it. The humidity should be be less than 20%, however, 15% is even better. Both soft and hard wood can be burned.
The combustion chamber is designed for wood logs up to 35cm lenght, and it has a capacity of ~50 liters.
The consumption depends mostly from the type and quality of the burned wood, but generally you can expect around 3-4 hourst of burning with soft wood and around 5 hours with a full load of hard wood.
If the chimney draft is strong enough, there shouldn´t be much smoke coming out of the stove. Before opening the doors you would open the exhaust fume flap, so most of the smoke can exit through the chimney. The best solution is not to open the doors before all the wood is burned down.
Removing the ashes from the upper and lower combustion chamber is done daily before lighting the stove. Once in a week you should remove the cast iron grids from the upper combustion chamber and clean the ashes out of the ash boxes below. This is done easily with an ash vacuum cleaner.
The heat exchanger is cleaned with long steel brushes which are delivered together with the stove. To clean the heat exchanger you must remove a cover behind the chimney tube exit on top of the stove. The fume channels lying below are then cleaned with the steel brushes while all the dirt falls down into the lower combustion chamber from where it can be removed with an ash shovel. This procedure is done every 6-8 month.
Every 2-3 years you will need to change the sealings of doors and cleaning openings. The injectorblock made of stainless steel and the cast iron grids will last for approximately 2-5 years, depending on how much the stove is murning. Refractory stones can get cracked on the surface which doesn´t neccessarily mean that they need to be replaced. Only after 5-8 years they will start crumbling, then you should replace them. In individual cases the glass of the lower combustion door can get opaque because of the extremely high temperature exposure, this will require a replacement glass.
In certain countries this is regulated by law, for example in Germany you would need 55L per 1kW of power output from the stove. So for the Walltherm this would mean around 600l as a minimum. We reccomend you to use a 1000l tank or even bigger.
The Walltherm woodstove delivers its energy to the storage tank, from there the heating system is fed. This means the heating pumps for the floor heating or for the radiators must not run, if the water in the storage tank is too cold. Otherwise cold water could circulate in the heating system. Some heating controllers don´t check the storage temperature before starting the heating pumps because the controller assumes there is an automatic heating source like a gas or oil burner connected to the storage tank. Such an automatic heating source would start heating the storage tank as soon as it´s temperature falls below a certain level. The Walltherm is no automatic heating source, so if the stove is the only heating source, the heating controller must check the storage tank temperature prior to starting the heating pumps!
The pump unit with the thermal 3-way valve ensures that the temperature of the water in the stoves heat exchanger remains at a level above 60°C during the burning. Condensation can occur on the inside of the stove if the water would be too cold, this would damage the stove over time.
Another result would be a worse burning and more unburned residues in the channels of the heat exchanger.
The 5 year warranty on the stove is only valid if it´s used with a properly working pumpg group with 3-way valve.
a) Chimney with enough natural draft
b) The floor/ceiling must hold a weight of 300kg for the stove or more if it´s inserted.
c) Pipes connections:
2 x pipes for flow and return (1“)
1 x fresh water connection
1 x drain
d) If combustion air is taken from outside, the air channel must least to the stoves position.
e) Distance to flammable objects must be maintained. Follow your local rules and regualtions but mostly 20cm of distance will be required. The stove must be placed on a non-inflammable surface (metal sheet, glass plate or stone)