Tempering furnace and method for assembling tempering furnace

A tempering furnace for a glass sheet, comprising a first furnace portion and a second furnace portion attached successively one after another in a lengthwise direction of said tempering furnace, wherein said furnace portions are configured to heat said glass sheet to a tempering temperature wherein:

• each of said furnace portions comprising a division channel inside said furnace portion arranged in a lengthwise direction of said tempering furnace for dividing air to blow enclosures having blow openings from which heated air is discharged as heated air jets towards said glass sheet to heat said glass sheet to a tempering temperature;
• said first furnace portion is provided with a blower configured for pressurizing air sucked from said tempering furnace and feeding said air to said division channel of said first furnace portion;
• wherein
• said division channel of said first furnace portion is connected to said division channel of said second furnace portion for leading air from said blower to said division channel of said second furnace portion;
• and
• one of said connected division channels is dimensioned to extend inside another of said connected division channels at least when in at temperatures prevailing during use of said tempering furnace.