Gas-fired heaters with burners which operate without secondary air and have a substantially sealed combustion chamber

A room heater comprising a burner having a combustion surface,

• a combustion chamber above said combustion surface,
• a source of gaseous fuel, air duct means delivering said fuel to said burner and operating in response to flow of said fuel to produce in said burner an air/fuel mixture containing an amount of air in excess of the amount required to cause complete combustion of said fuel,
• a bypass air passage separated from said combustion chamber by a wall,
• a powered blower producing substantial bypass air flow from an environmental air inlet through said bypass passage to a bypass discharge nozzle and operating to provide a jet of air directed to a heater discharge, said wall providing a heat exchange surface between said combustion chamber and said bypass air passage causing preliminary heating of said bypass air before it reaches said nozzle, said combustion chamber providing an exhaust open to said jet of bypass air, said jet of bypass air entraining sufficient combustion gases to produce a subatmospheric pressure in said combustion chamber and also mixing sufficient bypass air with the combustion gases to cause a safe temperature of the resulting mixture flowing through said heater discharge, said subatmospheric pressure in said combustion chamber resulting in an increase in the pressure drop across said combustion surface causing said air/fuel mixture passing through said burner to be greater than would be provided if said combustion chamber were at or above atmospheric pressure.