Hot water heater and steam generator

In a boiler comprising a housing having a top provided with a gas outlet, bottom, left and right sides and a front and back, the housing containing a manifold substantially parallel to the top, bottom and side walls, two sets of tubes, each set comprising a plurality of tubes, one set joining the upper manifold on the left and the other set joining the upper manifold on the right, the tubes of each set rising upwardly along their respective side wall, crossing the housing to the opposite side wall, rising adjacent the opposite side wall, re-crossing the housing to their respective side wall, rising therealong and eventually joining the upper manifold, the horizontal runs of the tubes of one set being vertically offset relative to the horizontal runs of the tubes of the other set so as to form a plurality of superposed chambers above the jacketed chamber, individual tubes of the sets being differently bent so as to form access openings from each chamber to the chambers above and below, the openings from chamber being offset so as to require a gas flowing through said chambers to traverse one chamber form front to back and the next chamber from back to front, means for introducing water into the boiler and for withdrawing steam from the manifold, and means for introducing a hot gas into the lowermost of the superposed chambers, the hot gas rising successively through the chambers which it successively and alternately traverses from front to back and then from back to front until it exits from the uppermost chamber through the gas outlet in the top, water flowing through the tubes being heated by the hot gas, the improvement which comprises a jacketed chamber adjacent the bottom of the housing and substantially parallel to the manifold, the lower ends of the two sets of tubes communicating with the jacket, the jacketed chamber being provided with at least one opening for passage of a hot gas into the next of the superposed chambers, the means for introducing water into the boiler introducing such water into the interior of the jacket from which it flows upwardly through the tubes, and a fuel burner positioned at least partly inside the housing so as to discharge hot combustion gas into the jacketed chamber, whereby upon burning fuel within said jacketed chamber the hot combustion gas rises through the chambers heating the water in the tubes.