Told by Iryna, a Ukrainian friend who grew up in Siberia:
As soon as the train departs, the provodnitsa asks around: “Are there any foreigners in this coach?”. If someone answers yes, she puts the heating on high. If none answers, she switches it off.
Maybe that is the reason why I always feel so warm on Russian trains?
I actually I found official guidelines on a Far-Eastern train.
In summer, the temperature is not supposed to exceed 28 if it’s above 30 outside, or 26 if it’s less than 20 outside. In winter, the temperature is not supposed to exceed 24.
That day, deep in February somewhere close to Khabarovsk, it was 24. Still, 24 is a bit a lot. No wonder why, as soon as you get on the train, you swap your boots and fur for slippers and pyjamas.