Hi everyone, I've been lurking for a while, but this is my first post.
Up in the Frozen North (I'm in central Alaska), all the busses are spec'd with Webasto or Espar heaters on them. The Thomas pusher I'm converting actually has 2 of the Webasto Scholastic heaters
, each rated for 45,000btu. I hadn't seen this configuration before... most of the busses just have one plumbed in series with the engine coolant loop that runs to the under-seat heaters and the driver's heater/defroster. Mine had a second heater added on a closed loop, hooked up to a couple water/air heat exchangers with custom ducts rigged up by the school district to blow hot air down a series of overhead vents on both sides of the passenger compartment.
I also have an old '82 MCI MC9 coach, and it came with a Webasto Thermo 350
that puts out 120,000btu.
I drove a shuttle bus for the local university for a couple winters, and even on a little 15pax busses, there was no way to get the temp up in the winter without the auxiliary heaters running. (They happened to use Espar E5's.) It didn't help that on-campus shuttle busses basically idle around at <20mph and never get a decent load put on the engine to generate some heat, plus they have the doors opening every minute or so letting the heat out. That little heater was a champ though. Even with the door open so often, it would keep it pretty toasty inside at -50*F.
As to using this type of heater for domestic hot water or cabin heat while stationary... either one could certainly be done, but I don't know that it's really the best tool for either job.