Coolant and potable water heater

A heater system comprising a burner having a burner tube, said burner being positioned within said burner tube, said burner tube being positioned within a coolant tank holding coolant, said burner tube being adapted to heat said coolant in said coolant tank, an exhaust manifold connected to said burner tube and being within said coolant tank, said exhaust manifold being adapted to exhaust combustion exhaust from said coolant tank by an exhaust duct extending vertically within said coolant tank and outwardly and vertically from said coolant tank, said burner tube having a longitudinal axis running horizontally, said coolant tank having a longitudinal axis running parallel to said longitudinal axis of said burner tube, said longitudinal axis of said burner tube being offset horizontally sidewise a distance from said longitudinal axis of said coolant tank, said exhaust manifold being positioned within said coolant tank sidewise of said burner tube, said coolant tank being connected to an expansion tank, said expansion tank being operable to receive coolant fluid from said coolant tank and to provide coolant to said coolant tank, a pump connected to said expansion tank to pump said coolant fluid from said expansion tank, a level switch within said expansion tank to indicate insufficient coolant fluid within said expansion tank and control means to shut down operation of said burner when said level switch indicates insufficient fluid within said coolant tank.