The Aquatherm range of boilers employ a well tried and proven design concept based on the reverse flame combustion technology pioneered in hot water boilers by YGNIS AG Switzerland. This reverse flame combustion method provides an economical and highly efficient three pass gas flow system. The design incorporates a large pressurised combustion chamber allowing the first two passes of gas to be made in the combustion chamber itself. The scrubbing action of the reversing flame causes the gases to enter and re-enter the high temperature flame zone many times before making the third and final pass through the smoke tubes. Turbulators in the smoke tubes further slow the passage of the combustion gases providing additional efficient heat transfer.