|In steam generation, wouldn't it be more economical to heat a small boiler and feed it just enough water for it to maintain its optimal steam generating temperature than to heat a huge boiler as is normally done? — MF, Gillette, WY
Not really. Once you have heated the water to its steam generating temperature, all of the heat you add goes into converting water into steam. The presence of more or less water just doesn't make any difference. The extra water requires no extra heat while the boiler is making steam. And having that extra water does act as a buffer in case you add too much or too little heat for a short while. That's probably why most boilers have a bit more water than they need over any short period of time. Furthermore, it's not always easy to add water to a boiler when the boiler's pressure is very high.