Wood boilers
Natural draught combustion with mechanical draught regulation and the E.S.T. system for sealed system installation. Two heat outputs: 29 and 40 kW.
Sphera 29
Sphera 40
Natural combustion, mechanical regulation
Sphera boilers use natural draught combustion: primary air is controlled by a mechanical draught regulator, driven by the temperature of the boiler body. As the water heats up, the regulator closes; as it cools, it opens again.
There is no control unit managing combustion and no sensors to calibrate. Regulation does not depend on electricity, which, for a wood-burning appliance in an isolated home or one prone to power cuts, is no minor detail.
It is a deliberate design choice: fewer components mean fewer things that can go wrong, and a machine that keeps working when others stop.
Why wood makes sense
The economic advantage lies in the fuel: wood has the lowest cost per kWh of all commonly available energy sources, and the gap with gas and heating oil has widened in recent years.
Where heating demand is high — a large house, a poorly insulated building, a business — the difference in annual heating costs is the main reason for choosing a wood boiler over a pellet or gas boiler.
Those with direct access to wood — woodland, their own land, a local supplier — benefit the most, because the fuel cost falls even further.
Instant domestic hot water, no storage tank
Both models produce instant domestic hot water, via a coil immersed in the water inside the boiler body.
No separate cylinder or storage tank is needed: the water is heated as it flows through the coil, the moment you turn on the tap.
For the system, that means one less component to install, connect and maintain.
E.S.T., sealed system installation
Traditional wood boilers require an open expansion vessel, placed at the highest point of the system — usually in the loft — with its own dedicated safety pipe. In a renovation this is a serious complication, and sometimes a problem with no solution.
E.S.T. — Evolution System Technology removes that constraint. The expansion vessel is built into the machine: the boiler is installed as a sealed system, like a modern heat generator, while the boiler body operates at zero pressure.
The system uses stainless steel heat exchangers immersed in the body. A discharge pipe lets water escape in the event of boiling, with automatic top-up.
In practice: no vessel in the loft, no safety pipe running through the house, and a system compatible with what the building already has.
29 or 40 kW
The two models are identical in design and operation: only the heat output differs.
Sphera 29 for average-sized homes. Sphera 40 for larger or poorly insulated buildings, or where the demand covers several units.
Sizing is based on the building’s heat demand, not guesswork: it is calculated by the designer or installer, taking into account volume, insulation, climate zone and heat emitters.
On a wood boiler, oversizing counts twice over: as well as running less efficiently, it means loading it more often than necessary.
What you need to install it
A flue compliant with UNI 10683, sized for the appliance and with adequate draught — on a natural draught boiler, draught is part of how it works, not a minor detail.
A plant room with space for the appliance and its maintenance clearances.
A connection to the existing hydronic system in the building. With the E.S.T. system, it is installed as a sealed system.
Space for the wood, dry and close to the boiler: loading is manual, so a convenient store makes a real difference to everyday use.
Frequently asked questions
Does it need electricity to work?
Primary air regulation is mechanical and does not depend on electricity: the draught regulator works according to the temperature of the boiler body. A power supply is still needed for the other components of the system, such as the circulation pump.
Does it produce domestic hot water?
Yes, instantly, via a coil immersed in the water inside the boiler body. No separate cylinder or storage tank is needed.
Is an open expansion vessel required?
No. The E.S.T. system builds the vessel into the machine and allows sealed system installation, with no vessel in the loft and no associated safety pipe.
How does it differ from a pellet boiler?
Wood costs less than pellets, but loading is manual: a pellet boiler feeds itself from a hopper or silo, whereas a wood boiler has to be loaded by hand. The choice depends on how much the fuel savings matter compared with convenience. See our pellet boilers.
How often does it need loading?
It depends on the heat output required, the type of wood and the weather conditions. Loading is manual, so it has to be done more often during periods of continuous operation.
How much maintenance does it require?
Regular cleaning of the firebox, the flue gas passages and the ash drawer, cleaning of the flue and annual servicing by a qualified technician.