High efficiency water heater construction

Claim 1

A multistage liquid heating apparatus comprising, in combination: a housing; burner means, within said housing, for burning a fuel and producing a heated gas including water vapor; a primary heating tank substantially adjacent and above said burner means; a secondary heating tank above said primary heating tank; a manifold interposing said primary heating tank and said secondary heating tank; liquid supply means for supplying a liquid to be heated to said secondary tank; transfer means for transferring said liquid from said secondary heating tank to said primary tank; outlet means for withdrawing liquid from said primary tank; a plurality of primary flues extending through said primary tank partially into said manifold, said primary flues communicating with said burner housing to receive heated gas, said primary flues being in heat transfer relationship with said liquid within said primary tank; a plurality of secondary flues equal or greater in number to the primary flues, said secondary flues extending through said secondary heating tank and from said intermediate manifold, said secondary flues being in heat transfer relationship with said liquid within said secondary tank; each one of said primary flues being aligned with one of the secondary flues to define a substantially linear flue passageway; one of said primary flues extending a lesser distance into the manifold than the other primary flues to define a condensate removal pipe from the manifold, to drain water from said manifold into the housing; and drainage means in the housing for receiving and discharging water from said condensate removal pipe.