What they do now is that the locomotives are laid up hot with fires on the grates. Everytime the watchman throws a couple of shovels full of coal on the fire you get smoke untill the green coal starts burning. By using an outside heat source, either a burner or a house boiler you can keep an engine hot with having to tend to a fire either as much or not at all. The use of a house boiler is not a new idea. It was used by several mainline operations in yesteryears. To me the use of the gas burner would be prohibitive considering the cost of natural gas right now,although the intial expense would be less than installing a house boiler capable of keeping a half dozen Mikes hot.