of finned or bare tube pipes 116 heat exchanger section 114 communicates with exhaust 26 for exiting the products of combustion to the outside atmosphere the high velocity high convective heat transfer rate of the products of combustion flowing from combustion chamber 22 through heat exchanger system 24 in a cross flow pattern enabling the heat exchanger system 24 to be very compact and efficient heat exchanger sections 102 and 114 are tapered to one side and have a drainage mechanism 120 and 122 where condensate will be trapped and removed from the unit drainage mechanisms 120 and 122 can be the type which accumulates a predetermined amount of liquid prior to draining the liquid another drainage mechanism 120 and 122 can be direct drains connected to the exhaust tube enabling the condensate to be drained off via the exhaust these liquid type of drainage mechanisms are well known in the art heat exchanger section 114 connects to exhaust 26 at 124 the high velocity super atmospheric products of combustion are exhausted through a small diameter pipe or tubing 126 to the outside of the building or dwelling one end of the pipe or tubing 126 communicates with heat exchanger section 114 and the other end.