Combustion heater

Combustion heater comprising

• first means defining a combustion chamber with inner and outer walls and an annulus therebetween and with a lower space within the inner wall having a forward end and rear end for holding an elongated solid fuel charge and means for feeding primary air thereto and combustion gas products therefrom both at said forward end so that the charge burns from said forward towards said rear end of said chamber,
• second means defining an elongated combustion gas products conduit running above and substantially parallel to the fuel charge space and within the flame produced thereby and having an entrance for combustion gas products of said first means,
• said first and second means being arranged to define an S-draft gas flow path,
• means defining a principal heat exchanger for receiving the exhaust of said conduit and extracting heat therefrom, and
• means for injecting secondary air into the combustion chamber outside of and adjacent to the exhaust conduit at multiple points along the length thereof to enhance flame coverage thereof,
• means for producing after-burning in said conduit by injecting secondary air therein at a point downstream of the conduit entrance, and
• means for preheating the primary air and secondary air and after-burner air in counter-current heat exchange in said combustion chamber annulus by injection to said annulus at the combustion chamber rear end and movement to said forward end.