Case 1:  Smoke evacuation in a pellet stove

Case 1: Smoke evacuation in a pellet stove

Stainless steel tubes A-316L have been fitted, as required by the pellet stove manufacturer and the norm UNE 123001 (as it is pellet, solid fuel), but when installing the stove in a given place in the home the following mistakes may be made:

  • Mounting a single wall tube as it is an outdoor installation in a very cold region in Spain.
  • Completing the installation with a 2.5 meter long horizontal section without inclination from the 90 degree elbow, after the first vertical section, from the stove exhaust pipe, leaving the installation without a natural draught. The picture corresponds to a pellet stove exhaust pipe in La Mancha. It can be clearly seen on the ground that the pipe drips all along the horizontal section.


  • Condensation all along the installation, especially along the horizontal section which the smoke reaches at low temperatures. The biomass smoke contains sulfur and chlorine which, under humid conditions, react chemically to produce the black liquid called creosote, highly corrossive, which results in a high rate of corrossion of the materials and their prematura aging. Specifically there appeared pores along the horizontal pipes through which the installation started to ooze onto the ground and walls causing them to get dirty. Eventually, the installation came to also drip through its final section.
  • Soot collection along the horizontal section as a consequence of not being cleaned when needed according to the installation necessities. Soot is deposited along the horizontal section. The forced ventilation of the stove is unable of pushing the soot out and lacks the help of the natural draught. The stove starts to show problems up to the point of reaching zero performance when it is no longer capable of expelling the smokes due to the soot blockage.

Proper solution:

  1. Mounting the isolated twin wall stainless modular tube A-316L /A304 to avoid condensation. Aggressive chemical reactions within the stainless tube can only be prevented by avoiding the rapid cooling of the fumes.
  2. Changing the location of the pellet stove (in the given case, to the other side of the window), which enables to mount a technically correct chimney installation (as vertical as posible), without loss of comfort within the home, though it may not be the “most beautiful” solution. In the given example, the installation could have been set in a more convenient way along a wall without windows.