High-tech and reliable


The benefits at a glance

  • High efficiency with advanced combustion technology, triple-pass heat exchanger and modulating output control (turndown ratio 4:1).
  • Maximum heat transfer with triple-pass heat exchanger.
  • High efficiency and ultra-low emissions with precisely controlled primary and secondary air.
  • Low maintenance with fully-automatic deashing, optional pneumatic cleaning system and flue gas deduster.
  • Advanced safety equipment ensures safe and reliable operation.
  • Maximum system performance with heavy-duty construction and all system components from one source.
  • Automatic ignition device limits idling and saves fuel (optional - only for fuels with >40% moisture content).
  • Custom design of your system by our team of experts.

Grate firing at its best

The Vitoflex 300-UF boiler uses a burner trough with an attached external grate and a moving annealing grate to achieve optimal combustion results. A feed auger moves the wood fuel into the burner trough where the fuel is pre-dried and gasified under precisely controlled primary air (underfeed combustion). On the external and the moving annealing grate the fuel completely gasifies (syngas). Precisely controlled secondary air is injected to fully combust the syngas and thermal energy is released into the boiler's triple-pass heat exchanger.

Quality design and construction

The Vitoflex 300-UF boiler is quality-constructed to handle the toughest of loads. The combustion chamber is lined with compressed firebricks with a high alumina content for added durability. All grate elements are made of durable cast chrome steel to withstand even the highest temperatures. The Vitoflex 300-UF boiler features a classic triple-pass heat exchanger design for maximum heat transfer and efficiency.


Clean-burning and efficient

Equivalent in quality to modern gas combustion, the advanced combustion process of the Vitoflex 300-UF keeps emissions of CO and NOx to levels comparable to those of modern fossil fuel heating systems.

Plus, unlike oil and gas, wood is a CO2-neutral, renewable form of energy. Used with our digital, modulating-output control, the Vitoflex 300-UF boiler achieves an efficiency of 85%.

Where can I buy a Vitoflex?

To get a quote for a new Pyrotec wood heating system including installation, please contact the biomass team at our head office:

Viessmann Manufacturing Company Inc.
45 Access Road
Warwick, RI 02886

Tel.    401-732-0667
Tel.    800-288-0667 (Toll-free)
Fax    401-732-0590

Email  info@viessmann-us.com

Product details


1331 to 4265 MBH - 390 to 11250 kW
Combustion type
Underfeed combustion
Maximum water temperature
250 °F / 120 °C
Pellets, woodchips with max. water content of 50%.
Application range
For apartment buildings, commercial applications and district heating, new buildings and retrofits.
Additional features
Fully automatic ash removal
Cutaway view


A perfect match – System technology

"The whole is greater than the sum of its parts." According to this philosophy, Viessmann does not just make individual heating equipment components that meet the high Viessmann standards for quality, reliability and effectiveness. Rather, all products are part of a matching concept, where all components complement one another. Only the perfect interaction of system integrated components draws out the maximum potential of our innovative leading technology.

Viessmann system technology includes everything you need for a reliable and economical heating system. The Vitotronic control unit with remote control, the powerful Vitocell DHW tanks for best DHW convenience, to high-quality solar thermal systems for cost-saving heating.

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