air flowing along chamber 15 preheats air flowing along chamber 14 also air flowing along chamber 14 preheats the air flowing along chamber 13 this leads to a very efficient and uniform heating process the effect is heated air that is exceptionally uniform and well heated and that is very quickly evenly heated during start up of the heater s 20 our test data suggests to us that the present room heater 20 has a substantially improved efficiency and uniformity of heated air flow over another well known stand alone heated forced air room heater in generated air temperature by as much as 25 during constant operation specifically we measured the present room heater 20 to provide a temperature of about 210 degree f while one known prior art room heater was only able to provide a measured temperature of about 155 degree f at a similar output location and time period we are still trying to understand and explain this improvement but believe it to be related at least in part to the efficient and uniform heating of air provided in the present room heater 20 which is due in significant part from the preheat and air chamber arrangement s of the present room heater 20 we believe our design leads to considerably more efficient and uniform heating of air over known prior art room heaters due to less turbulence and less u201c hot spots u201d even when they have a heater element with similar btu hour rating and heating capacity the room heaters.