Air heating apparatus

Claim 1

THE COMBINATION OF: (A) A DIRECT-FIRED HEATER HAVING FIRST BLOWER MEANS FORCING A FIRST DRAFT OF AIR THROUGH BOTH A COMBUSTION CHAMBER AND A SEPARATE VENTILATING AIR PASSAGE IN HEAT EXCHANGING RELATION WITH SAID COMBUSTION CHAMBER; AND (B) APPARATUS ADAPTED TO BE RELEASABLY COUPLED TO SAID DIRECT-FIRED HEATER FOR CONVERTING IT TO AN INDIRECTFIRED HEATER, COMPRISING; (C) A CASING CONTAINING A HEAT EXCHANGER CONNECTED TO RECEIVE INTERIORLY COMBUSTION GASES FROM SAID COMBUSTION CHAMBER AND CONDUCT SAID GASES TO AN OUTLET; (D) SECOND BLOWER MEANS INCLUDING AN INLET OPEN TO ATMOSPHERE CREATING A SECOND DRAFT OF AIR SEPARATE FROM SAID FIRST DRAFT; (E) MEANS DIRECTING A MAJOR PART OF SAID SECOND DRAFT OF SAIR AND THAT PART OF SAID FIRST DRAFT EXISTING FROM SAID VENTILATING AIR PASSAGE INTO SAID CASING AROUND SAID HEAT EXCHANGER TO A VENTILATING AIR OUTLET; AND (F) MEANS FOR DISCHARGING THE REMAINING PART OF SAID SECOND DRAFT IN A DOWNSTREAM DIRECTION INT THE FLOW OF SAID COMBUSTION GASES.