Gas equipment is calibrated for a specific fuel family (1H, 1E, 2H, 3P, etc.) and reference gas (G20, G25, G31, G30). If an installer mounts a G20 (natural gas H) unit on a grid that delivers G25 (natural gas L) or LPG (G31), the unit operates at the edge of failure.
Short glossary
G20 = natural gas H (High calorific value). Wobbe index 50 MJ/m³. Most of Slovenia (Geoplin grid), Austria, Germany, Hungary. Grid pressure 20–25 mbar.
G25 = natural gas L (Low calorific value). Wobbe index 41 MJ/m³. Netherlands, parts of northern Germany. In Slovenia rarely encountered, occasionally on the northeast border.
G31 = propane LPG. Wobbe index 80 MJ/m³. Pressure 37–50 mbar. Used where there is no grid: industrial zones without connection, agricultural halls, construction sites, seasonal buildings. Tank or cylinder bank.
G30 = butane. Rarely used in industry. Occasionally for seasonal portable units.
G25.3 / G27, variants in specific regional grids (Slovakia, Czechia). Important: if you plan to export or install in another country, ask about the local gas family.
Equipment categories
Gas equipment carries a category label on the data sheet and rating plate:
| Category | Gases | Typical use |
|---|---|---|
| I2H | G20 only | Slovenia, most of EU |
| I3P | G31 only (propane) | Mobile units, off-grid |
| II2H3P | G20 + G31 (convertible) | Most common industrial universal model |
| III1a2H3+ | G110 (mine gas) + G20 + G30/G31 | Special applications |
The Solaronics SRII range is category II2H3P: one unit, two convertible regimes. Conversion means replacing the gas jet and adjusting pressure. An installer task, 30 minutes.
How to identify your gas
Request a gas supply specification (data sheet) from your distributor. In Slovenia, Geoplin and local DSOs (Energetika Ljubljana, Plinarna Maribor) issue a specification: Wobbe index, connection pressure, calorific value. No installation should start without this.
Check the rating plate of existing units. An old gas boiler or unit heater carries a plate with "G20, 20 mbar" or "G31, 37 mbar" etc. If you have several old units with conflicting plates, prior installations were never verified, call the distributor.
LPG tanks: an LPG tank outside the building means your unit needs G31 (propane) or G30 (butane) configuration. Seasonal butane/propane blends exist, but the industrial standard is pure G31 propane.
What happens with the wrong configuration
Wrong: G20 unit, G31 grid. Gas jet too small for propane. Unit never reaches nominal power ("heats but never reaches setpoint"). Instantaneous efficiency drops to 78 %, visible flue gases.
Wrong: G31 unit, G20 grid. Gas jet too large for natural gas. Excess consumption, heat-exchanger overheat, short service life.
Wrong: pressure mismatch. A 20 mbar unit on a 25 mbar grid means 15 % overconsumption; a 37 mbar (G31) unit on 50 mbar means unstable flame and automatic shut-off.
Practical advice
When ordering equipment, always include the Geoplin (or equivalent distributor) gas supply specification. Solaronics technical support verifies compatibility before dispatch. Without that document the unit ships in category II (universal) unconfigured, which means a second order cycle and unnecessary cost.
Related: heating-power calculation depends on the gas's calorific value, G31 propane and G20 natural gas differ by 60 % in Wobbe index.