Essential Information

The SEMAX OPTI boiler is a boiler that gasifies pieces firewood in accordance with the 303-5:2021-09 standard. It is an ideal solution dedicated to people who have large stocks of properly stored firewood – hornbeam logs (logs) with a humidity of Wc=15-20%. . Operating our device at nominal power allows for better use of fuel and, as a result, cleaner exhaust gases emitted into the atmosphere. Additionally, the boiler is equipped with automation that regulates combustion and operation of the device. For proper operation of the entire system, the boiler must be connected to a buffer receiving excess heat.

Available powers: 16kW
Fuel: firewood, pieces
Certificates: EcoDesign | 5 class
Energy class: A +

Key benefits


Heat exchanger

Heat exchanger | horizontal convection channels | shelf and tubular
Efficient design for quick cleaning of the exchanger from the front. The design of the boiler exchanger ensures high heat removal from the furnace.

Flue outlet

At the back of the boiler | top and side adjustment from the fan
The structure of the boiler has been designed in such a way that the flue outlet is at the rear. The use of such a solution in a central heating boiler allows the flue to be directly led out to the chimney.

Exhaust gas temperature sensor

Together with the controller, the sensor controls the exhaust gas temperature.

Exhaust fan

Adjustable height
It is attached with an adapter to the rear vertical wall of the flue. The fan produces the necessary thrust needed for efficient fuel combustion.

Secondary and primary air intake

Secondary air is sucked in through six openings in order to fully burn the fuel. The amount of secondary and primary air can be adjusted with shifts.

Smoke exhaust hatch

It allows for effective removal of smoke from the furnace chamber.

Baffle plates

Mounted in the convection channels, baffle plates effectively reduce the exhaust gas velocity, maintaining high heat transfer to the water jacket.

Ceramic channel

The use of ceramic plates as a ceramic channel contributes to the improvement of combustion efficiency. These screens increase the temperature in the combustion chamber, extend the path they have to travel within the boiler, and trap particles floating above the furnace, further burning them. This results in an increase in the thermal efficiency of the boiler, while reducing the amount of environmentally harmful compounds emitted in the exhaust gases.

Buffer tank


Provides optimal working conditions for the boiler. The boiler can operate at optimal power, and the excess heat is stored in the buffer. The heating system of the house takes as much heat from the buffer as it needs at the moment.

Central heating boiler can only be installed in the heating system together with a buffer cylinder. The tank is not included in the price of the boiler.

Boiler control

The TECH ST-880 controller with PID is programmed to automate all processes related to home heating. Your role is only to enter the temperature you want in the room, and the controller will optimize combustion in this respect. Entering the advanced settings of the controller, you will be able to personalize many parameters related to combustion in the boiler, depending on your preferences!

Key features:

One CH.1 mixing circuit with room thermostat
Pump (DHW, CH, additional)
RTC clock with weekly timer
Weather control
Winter / summer operation mode
FuzzyLogic & PID

Standard equipment

Exhaust set which includes the TECH ST-880 controller with PID + exhaust fan. The controller also supports the buffer tank required to install the central heating boiler.

Pump: C.O.1; Domestic hot water; additional
One CH.1 mixing circuit with room thermostat

Optional equipment:

TECH ST280 room thermostat (touchscreen, wired)
Room thermostat TECH ST 280 + ST 260 (touch, wireless)

Manual firing up

Firewood – hornbeam logs (chips) with a moisture content of Wc = 15-20%. Properly seasoned wood is an ecological fuel that meets all standards. It is completely natural, as a result of combustion, biodegradable ash is produced. By burning properly seasoned wood, we produce a small amount of harmful compounds into the atmosphere.

Technical data of the boiler

Nominal thermal power [kW] 16
Boiler power range [kW] 16
Heatable surface* [m2] 160-240
Water capacity [L] 71
Maximum working pressure [bar] 3
Maximum working temperature [°C] 80
Test pressure [bar] 4,5
Glade circumference (tribe) [cm] 30-40
Log length (strain) [cm] 26
Fuel [-] firewood, pieces
Electrical connection [-] 1A; ~230V; 50Hz
Electric power consumption [W] 70
Temperature controller setting range [°C] 60-80 (every 1°C)
Chimney draft required [Pa] 23
Heat storage capacity (buffer) [L] 600
Boiler weight [kg] 342

* A new building with very good thermal insulation was adopted for the calculations.

Certificates, class, boiler emission

Ecodesign [-] Yes
Boiler class [-] 5
Energy class [-] A+
Seasonal particulate emissions [mg/m3] 20
Efficiency for nominal power [%] 88,85
Nominal emissivity of the particulate matter [mg/m3] 15

Boiler dimensions

A [mm] 490
B1 [mm]
B2 [mm]
C1 [mm] 1380
C2 [mm] 1260
D1 [mm] 1070
D2 [mm] 730
E [mm]
F1 [mm]
F2 [mm] 713
F3 [mm] 470
F4 [mm] 82
G1 [mm] 159
G2 [cal] 1 1/2
G3 [cal] 1 1/2
G4 [cal] 3/4
H [mm] 30
W [mm] 290×200
X [mm] 290
Y [mm] 510
Z [mm] 330

Boiler documentation

DTR instruction

Technical and operational documentation Download

Driver manual

ST-880 controller manual Download

EcoDesign certificate

The boiler complies with the requirements of the EcoDesign standard (EkoProjekt) Download

Energy label

A + energy class Download

Product sheet in accordance with EU regulation 2015/1187

According to EU Regulation 2015/1187 supplementing Directive 2009/125 / EC of the European Parliament and of the Council Download

Product sheet in accordance with EU regulation 2015/1189

Compliant with the EU Commission Regulation 2015/1189 of April 28, 2015 Download

Foreign sales

Paweł Czepiel

Export manager
Language: Russian, English
Monday-Friday (7:00 a.m. - 3:00 p.m.)


+48 663 45 32 22
+48 85 711 94 54 ext. 17



METAL-FACH Technika Grzewcza Sp. z o.o. reserves the right to introduce changes to the technical parameters, equipment and specifications of the offered goods without prior notice.

General contact:

Opening hours:

  • Mon.-Fri. 7:00a.m.-3:00p.m.
  • Phone: +48 85 711 94 54 int. 17
  • E-mail: p.czepiel@metalfach.com.pl

General contact:

Service contact:

Opening hours:

  • Mon.-Fri. 7:00a.m.–3:00 p.m.
  • Phone: +48 85 711 94 54 int. 17
  • E-mail: p.czepiel@metalfach.com.pl

Address data:

METAL-FACH Technika Grzewcza
Sp. z o.o.

  • st. Sikorskiego 66, 16-100 Sokółka, Poland
  • NIP: 545-182-60-12
  • REGON: 523566030

How to get: