I have searched for a beatiful photo of large Swedish locomotives standing on parade in the dark, in front of the turntable and an enginehouse.
The thing is, all the locomotives had their blowers slightly cracked, and the slight steamplumes shimmered in the artificial lighting.
I don't know what time of dark day or night, but there were no people around, and the building was not lighted indoors.
To me, it's always been obvious they had a small fire going, to be prepared for service in short time.
At least in Germany, it was not uncommon to have an auxilliary locomotive by the engine houses, just for supplying steam for powering the blower in an other locomotive, when firing up.
In Sweden, there is the added problem of keeping all piping from freezing during nightrest. Keeping all valves slightly open, is aparently not entirely a good idea in strong cold, because the weak flow actually just makes shure there is water in the pipes that freezes. One engineer of the time (ca 1940), wrote that the easiest, was just going around with a showel with burning coal, and hold it under frozen parts before service. (I don't know if it is true, but in Siberia, a can with burning diesel could be put under the engine block of trucks, to make the crankcase oil flowable. ;-) )
I cannot swear to this, but I believe locomotive boilers were only allowed to cool down for mechanical service and repair. And after such complete cooldown, heating the boiler was done rather slowly, to reduce thermal stresses to the boiler and increase service life.
On matters of fuel, Sweden has no coal. We do however have a lot of running water from the mountains (like Norway), so electrical technolies were developed very early. Electrical power generation and also electrical train operation started already1900! And electric locomotives have since been been exported around the world. (Amtrack uses a type first introduced in the 1970-ties by ASEA / ABB. The technology was groundbraking.)
The last steam locomotives were delivered 1916. By 1933-36 all major lines had been elctrified, and there was no service for these large locomotives. At that time, steam operation was in essence over in Sweden. The development of the type "F" series took many years, and commenced at a time when steam operation already was destined to end in Sweden.
However, these beatiful state of the art type "F" series, were favourably sold to Denmark, who needed locomotives, and planned to go on with steampower. And so these 11* little used locomotives were sold to Denmark at very favourable price, along with a good stock of spares. And did good service with the Danish State Railways into the 1960's. (* I don't remember the figure, but original planning was to build a couple of dozens of the type "F", but halted, as it became all to obvious that the weren't needed. I seem to remember the Danish benefitted particularly, because of this, the spare part stock was very generous. ;-D)
After the sale in 1936, of these last built Swedish steamlocomotives, steamlocomotives were only kept as wartime backup.
The lack of coal reserves in Sweden has been a historical headache. So huge amounts of charcoal was produced, since forrest is abundant. It was hellish bad payed work, for lonely men attending their own "mila" out in the woods. If the "mila" pile caught on fire, all was lost, and hence no pay at all. So it had to be watched around the clock by these lonely men.
The Swedish steel industry of course needed enormous amounts of coal. So my grandfather had a perpetual shippingbusiness, importing coal to the steelmills in northen Sweden, one way over the Baltic sea from Poland and Germany, and the other way he filled the ships with steel.
Anyway, steam locomotives in Sweden have been fueled both with charcoal, and proper coal - as well as with wood! Which however is very unpractical, due to the lower energy density.
During WWII, a lot of the steamlocomotives in war reserve, were however prepared for wood firing.
There is a nice continuation of the Swedish series "F" locomotives. In 1963 after active service in Denmark, the Swedish State Railwaymuseum bought two of the engines "back to Sweden". F1200 has been restored to original condition, and runs rather often. It has avery nice blue color. (In my memory, is slightly more like clearblue. Maybee I've always seen it i bright sunshine! :-D In the film the color looks too greyish in my mind. The F1202 has been stored, but is now beeing renovated.
At the end of the trainset in the video, my childhood favourite electric locomotive, the "Rapid" series, is beeing towed. I have actually considered building it in 1:32. A nice engineer at the ASEA factory actually sent me huge original blueprint drawings. (Yes, I'm old enough to literally know what a blueprint is. I also found my school textbook on drawing standards the other day. ;-) I wish I was just a little younger, then I would have learned CAD. I'm to lazy now.)