Chimney and draught requirements

General requirements. The chimney must be well-sealed and insulated, to avoid condensation of water vapour and fall out of flamable tar in a flue. We recommend to insert a stainless steel liner into a brick (masonry) chimney. It improves draught of the flue and prevents the brick chimney from seeping of moisture and  by-products of combustion through porous brick and mortar. The flue liner must be round or oval. We do not recommend to use a rectangular liner, as due to temperature fluctuations, its walls deform, cracks appear at the liner sections junctions, through which the condensate seeps into the bricks, and an additional air sucks in, thus reducing draught of the flue. The draught strenght should correspond to the value stated for each Astra G wood gasifying boiler in the Technical data table. The flue liner should be industrially made, certified and installed by professional installers. Only one heating appliance is allowable to connect to each flue.
Chimney dimensions. Minimum permissible height of the chimney should be at least 6 m, the height of 7-8 m is optimal. The required height of the chimney could be affected by obstacles present around the building- trees, other buildings, etc. The  chimney cap should be above a ridge at least by 0,5 m. If the chimney stands further than 1 m from the ridge, the angle horizon- ridge- the cap of the chimney should consist 10° or less degrees. Internal diameter of the liner should not be smaller than the diameter of flue outlet of  Astra G wood gasifying boiler.
Weak draught puzzle. Astra G wood gasifying boiler will operate in effective way if the draught in the chimney is sufficient (the required draught value for each Astra G boiler model is shown in Technical data table). If you are not sure about chimney‘s draught strenght, it could be gauged. In case if weak draught is determined, some solutions are worth to consider:

  • reconstruction of the chimney with purpose to raise its height and/or widen the flue channel. However, in most cases this way is hardly achievable;
  • mounting a new insulated metal chimney outside the building,
  • mounting a suction fan inside the current chimney‘s flue,
  • mounting an in-feeding fan in the wall or window of a boiler room to raise pressure in it by intaking additional amount of air.

Which method is the most suitable in a particular situation, decision has to be chosen after consulting with professional chimney inspectors or installers.

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