If a loco is going to be sitting for an extended time, it will either have the fire knocked out, or it will have the fire banked... Both are good for a loco sitting around overnight (for example).
If you knock the fire out, it will of course cool down quite a lot, and will require a near cold start the next day (the little tank locos at Puffing Billy generally still have about 5-10PSI after sitting for 12+ hours without a fire...).
If you bank the fire, it'll keep the loco warm but not 'full steam hot'. You can bank a fire somewhat in Trainz. 100% coal level is optimal fire, higher is heading towards a 'banked' fire. Under 100% is heading towards a thin, and after a while, cooler fire.
So, if you don't mind doing a few minutes 'prep' on the steamer in your session, bank the fire (150% may be a start, possibly 125%; not really tried it much sorry), have about 95% water in the boiler, and leave the blower shut. When you're ready to take the loco for a run, crack the blower until you see pressure starting to increase. Once it starts increasing, your fire is hot and it shouldn't drop too much when you start driving. You may need the blower cracked a little, depending on the loco.
As to using an electric,etc, blower. This is only used for a cold start. A lot of sheds have smokestacks built into them as well. These have two purposes, one is to exhaust smoke out of the shed, the other is to increase the chimney/flue length which increases the draft without the blower running.
As to a cold start, I know a few people who have developed 'warm start' locos (not stone cold, but not hot either) that take an hour or so to warm up, however Trainz won't handle a stone cold start. Considering a stone cold start is several hours (a small boiler can be bought up to about full pressure in 2-3ish hours if in a hurry, a large boiler generally requires a lot more time than this!), I really don't see the need to model it in Trainz, beyond a curiosity...
Regards
