Abstract: The present invention is directed to an apparatus for heating hot water. The present apparatus utilizes at least two individual hollow conduits that pass through the interior of a hot water tank. Independent inshot gas burners mounted in the conduits pass hot air through the hollow conduits warming the water surrounding the conduits. The conduits are organized in the interior of the tank in such a manner as to create distinct differential temperature zones. Each such temperature zone has an associated hot water outlet. The inshot burners are regulated to maintain the temperature zones. In this manner, the user is able to utilize the advantages of an internal coil heating system but has the ability to draw steady supplies of water of varying temperatures from the tank which is critical for many modern residential and commercial hot water and hydronic systems.

Abstract: Device for heating fluid, comprising: a first section for heating the fluid in which fuel and air are mixed and combusted; a second section for heating the fluid which is disposed substantially in the line of the combustion section and in which a number of pipes for the fluid extend substantially transversely of the flow direction of the combustion gases; and a third section for heating the fluid which is disposed substantially in the line of the second heating section and in which a number of pipes for the fluid extend substantially transversely of the flow direction of the combustion gases, wherein at least a number of the pipes in the third section are provided with ribs or fins enhancing the heat transfer.