Water heater with heat insulating coating on tubes

Claim 1

A CONTINUOUS FLOW WATER HEATER COMPRISING: AN INPUT CHAMBER HAVING MEANS TO RECEIVE WATER TO BE HEATED; AN OUTLET CHAMBER HAVING MEANS DELIVER HEATED WATER FROM THE HEATER; A PLURALITY OF SUBSTANTIALLY PARALLEL, GENERALLY HORIZONTALLY DISPOSED HEAT EXCHANGE WATER TUBES INTERCOMMUNICATING SAID CHAMBERS; MEANS TO PASS WATER-VAPOR LADEN FLUE GASES IN CONTACT WITH THE EXTERIOR OF SAID TUBES, SAID TUBES RECEIVING WATER FROM SAID INPUT MEANS AT A TEMPERATURE BELOW THE DEW POINT OF SAID GASES AND DELIVERING HEATED WATER AS A LIQUID TO SAID OUTLET MEANS; AND A HEAT RESISTANT AND HEAT INSULATING COATING ON THE OUTER SURFACES OF SAID TUBES AT LEAST BETWEEN SAID INPUT CHAMBER AND A POINT ALONG THE LENGTH OF THE TUBES AT WHICH THEIR OPERATING SURFACE TEMPERATURE IS ABOVE THE DEW POINT OF SAID GASES, SAID COATING HAVING SUFFICIENT INSULATING PROPERTIES TO MAINTAIN THE TEMPERATURE AT ITS EXTERIOR SURFACE ABOVE SAID DEW POINT AND DECREASING IN THICKNESS FROM SAID INPUT CHAMBER ALONG THE LENGTH OF THE TUBES IN ACCORDANCE WITH THE RISE IN TEMPERATURE OF THE WATER PASSING THROUGH THE TUBES.