AS devotees of Steamboatin', we tend to look disapprovingly at other prime movers such as diesel and gasoline engines.  Noisy, disagreeably smelly, uninteresting, and the like, while we boast about the fine attributes of our finely handcrafted steam machinery.
Steam Power is Inefficient:  Unfortunately steam, with all its beauty, mechanical ingenuity, traditional and nostalgic appeal has been replaced for a very good reason--efficiency.  A generally accepted figure is that steam machinery is about 8% efficient.  That is, of the heat (energy) produced by the burning of the fuel, only 8% produces work at the drive shaft.
A steam plant is a heat engine, thus it follows that inefficiency results either from heat loss or from heat transfer.  The biggest heat loss occurs at the boiler via the stack; minor heat losses occur from the engine, associated piping, and accessories.
Heat transfer problems occur mainly within the boiler and within the various heat exchangers used in the particular system.  Rather than accept these inefficiencies as inherent to our steam plant, let us look at the great  increases in efficiency that can be achieved quite simply.
A brief look at the arithmetic involved:  If we can, by our corrective action, measure increases efficiency by 2%, say from 5% to 7%, or from 6% to 8%, then the horsepower at the drive shaft can be increased by 1/4 to 1/3.  Quite a large improvement!
1. Capture Stack Heat:  Obviously our prime effort must be to do some thing about the tremendous waste of heat going up the boiler stack.  Insulate the stack to keep the waste heat in place, also a cool stack has many comfort and safety advantages.  Metalbestos double wall insulated stainless steel stacks, lagged with sheet brass, if desired, performs this task conveniently and economically
now let us add preheater and super heater coils to he interior of the stack thus partially recovering the stack heat.  If one can be certain that the feed water lines can always be full of water (a rare circumstance) copper tubing may be used.  Otherwise this and the superheater should be made of stainless steel tubing which, when dry, will tolerate the stack heat.
2. We must Insulate:  Our second effort should be insulating.  Adding one to two inches of glass insulation to the exterior of the boiler covered with wood or metal lagging is a good start.
Then insulate the steam lines: main steam line boiler to engine, cross over from HP exhaust to LP steam chest, the engine cylinders themselves, engine exhaust, exhaust/feed water preheater, Feedwater line to stack preheater, and then from stack preheater to boiler.  Keep the whistle feed line inside the stack.