Heat-preserving boiler

Claim 1

The combination with a heat-preserving boiler, including a water tank therein, a flue pipe extending vertically through said water tank, a combustion chamber disposed under said water tank, water admission means, and water delivery means connected with said water tank, of a tubular drum having a wall at its upper end spaced from and surrounding said water tank to form an annular downward outlet air passage between the outer surface of said water tank and the inner surface of said drum, the upper end wall of said drum defining a ceiling above said flue pipe, a tubular cover having a wall at its upper end with an opening therein and positioned over said drum to form an annular upward outlet air passage between the outer surface of said drum and the inner surface of said cover, a tubular housing having a wall at its upper end with an opening therein and disposed over said cover to form an annular inlet air passage between the inner surface of the housing and the outer surface of said cover, said inlet air passage being connected with said combustion chamber through openings at the lower end portion of said cover, an inlet duct communicating with said inlet air passage and connected to said opening in the upper wall of said housing, and an outlet duct connected with said opening in the upper wall of said cover and communicating with said outlet air passages to lead exhaust air to atmosphere, said outlet duct being disposed within said inlet duct to form an extended inlet air passage between the outer surface of said outlet duct and the inner surface of said inlet duct.