I am reminded of another design issue, capacity to warm up, vs keep warm.
If a busnut is out using the coach in cooler weather, the goal is continuous, keeping the coach warm. That is a very different capacity than warming up a cold coach.
For those used to air conditioning, you know the same issue from the other side, it is easier to keep the coach cold, than to cool down a hot one.
The difference between warm up and keep warm is wide enough, that aiming at one, will compromise the other.
The challenge is how to throttle a heat source that makes xxxxx BTU, when the interior only needs 5-10k to keep an evening chill off, but needs to be able to put the whole xxxxx BTU into the interior on returning to the coach in cold weather when away at some event, where leaving the coach heat on was not allowed or desired, or when Old Man Winter follows the snowbirds south.
A hint: "wasting heat" to the engine block may be VERY desirable, to tame a big coolant boiler under warmer weather conditions. Sure, open a window, make a draft, make the Admiral miserable again...
Also, on those cool evening chill type scenarios, after a day's drive, along with the whole coach already being "at temperature" there's over 2000 lbs of cast iron down the back that isn't going to be cooling off for a long time that can be tapped without burning any more fuel.
The first evening, the bedroom is lovely, the second evening, the engine has gone cold, and now the bedroom isn't lovely...
Keeping the inside temperature from varying wildly, under all these different conditions is really tricky, and as usual, the forums are skinny on reports of failures, only reports of successes...
The electrical power consumption of the heat distribution system often makes trouble. Fans, pumps, burners all consume battery power, at a time when most battery bank capacities are also challenged by colder temperatures.
Just as an example, running the stock coach HVAC fans in an MC8 via a bypass switch, a DBW300 firing and circulation pump running, and water valve cycling, draws about 11 amps of 120 VAC via a shore cord feeding a Trace 4024 inverter, supplying the 24 volts to a set of topped-up house batteries. That's somewhere around 1320 watts burning a hole in the coach's electric budget.
What is the consumption of available fan units?
Check the newer low floor transit coaches, they are running radiant heat the length of the sidewalls where the duct work used to be... That copper pipe and aluminum fin radiator has a rating per foot, at a certain water temperature... if I could find it again...
So much fun playing with the variables.
happy coaching!
buswarrior