• Elegant and efficient: Walltherm® woodstoves
    Walltherm® woodstoves
  • Elegant and efficient: Walltherm® woodstoves
    Elegant and efficient: Walltherm® woodstoves

Walltherm® Arunda

The stove with a stone on the front

With the model Arunda we give you the possibility to add a stone slab to the front of your Walltherm stove.

The heat output is the same as for the Zebrú model.

We recommend using heat-proof stones like marble, granite or soapstone.

We sell the stove without the front slab, but we provide a dimensioned drawing, so you can ask a local stone mason to produce it for you.

Technical data

  • Power: 14,9 kW
  • How the heat is divided: 70% to the water, 30% radiant heat
  • Efficiency: 93 %
  • 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 WAL04:

Based on a digital solar thermal controller, this special version called WAL04 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.
The controller WAL04 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.

Items deliverd with the stove:

  • Walltherm Arunda stove
  • Pump group with 3-way valve and high efficient pump
  • Fittings
  • Utensils (broom, poker, ash scoop)
  • Cleaning brushes
  • Instruction Manual


Frequently asked questions

Whan type of chimney is needed for the Walltherm to work properly?

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°.

Will there be condensation in the chimney because of the low exhaust temperatures?

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.

Which wood is needed?

piece of wood

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 length, and it has a capacity of ~50 litres.

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.

Does smoke come out of the stove when putting more wood in it?

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.

What do I need to know about cleaning the stove?

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.

What are the wear parts and how often do they need to be changed?

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.

Which size should the storage tank be?

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.

Are there some special requirements to the heating system?

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!

Why is the stove connected trough a pump unit with a 3-way valve?

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.



Which requirements does the location need to meet?

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)