(under subclass 412) Feed water heaters in horizontal fire tube boilers and located either within the smokebox or forming a part of the smoke box structure.
(1) Note. A "smokebox" is distinguished from a "smoke chamber" in that the former consists of a closed chamber at the end of the boiler, into which the products of combustion pass directly from the fire tubes and thence to the smokestack, while a "smoke chamber" is a chamber at the end of the boiler, into which the products of combustion enter either from the fire tubes or from the flue outside of the boiler and do not pass directly out of the chamber, but may return through other boiler flues.
SEE OR SEARCH THIS CLASS, SUBCLASS:
151, for a return fire tube boiler having a smoke box containing water tubes.
