I remember in the 1980s Wilts & Dorset used paraffin heaters to "thaw out" the buses in the morning, the smell being quite distinct if you were on one just out of the depot.

 
Heating a diesel bus cant be hard, there is almost unlimited waste heat from the engine. To avoid over-cooling the engine use a thermostatic radiator fan that only runs when the engine coolant reaches say 75 degrees.
In the colder parts of the UK, mains powered electric preheating should be considered.

 
All part of the fun being a Cornish bus driver!
Cornwall was the dumping ground for everything old when I started driving.
So rarely did the driver have heating, and frequently got drowned going round corners or braking with water coming in from above your head.
Passenger heating - luck of the draw!
Windscreen blowers sometimes worked, sometimes didn't.

Then a slow progression to 'renew' and we still got wet, but heating slightly less of an issue.
The progress has now stopped, and Cornwall is returning to a dumping ground for older vehicles again with First.

Yes, management always took the issue of heating and water ingress seriously.
Unfortunately the engineers didn't have the budget to order or find spares (or time to fit them)!

 
Always a bit worried about the drivers, one having picked me up from a notoriously cold stop the other night and he was a bit blue around the edges too.

Mark

 

Optares are about the only modern vehicles that are fitted with heating. It’s forced through the vents at the rear seats from the engine bay.

 

This reminds me of the 1960s when I was a schoolboy travelling on London buses.  Most of my journeys were on the older buses, RT/RTL/RTW, and these had no heating at all.  Until latterly some of them had a small heater fitted underneath one seat at the front right of the lower deck.  Oh the delight of getting the seat behind the heater and warming my cold feet on that heater!  And then we got the luxury of an occasional journey on the new Routemasters, which had the built-in warm air heating outlets, on both decks.

 
The current sustained three degrees centigrade (and flurry of cancelled services) and also the memory of making it to the seats at the front and downstairs to sit within reach of a small grill that emitted warm air - on what may have been a London routemaster... all this  caused me to reflect on 'Heating on buses' which in 2025 often doesn't seem to be a thing.

It's so much not a thing that I wondered if Optare buses might actually be not fitted with heating for the passengers at all. Looking *that* up though, they do.

Then, the next hit on the web search was to a couple of threads in railforums with wry observations that various bus companies turn off the heating in winter as that benefits the engine - and then turn it on in summer to provide additional engine cooling - and then an interjection from another bus operator that he was passionate that his firms bus's did not run with heating defects and that any that did were repaired immediately. Where the truth is in all this I'm not sure.

Mark