The implementation of fire heating is a bit hacky and wouldn’t easily support neither uniform heating nor cooling.
This is a recurring feature request (like vehicles-in-vehicles), but unfortunately it would be quite hard to implement well.
Current implementation works like this: fields of hot air gas are created, then they spread around like smoke.
This works, but is slow (major reason of why fires are so CPU-intensive), wouldn’t stabilize nicely in big rooms, wouldn’t work in moving vehicles and makes hot air rather “viscous” (opening a window doesn’t make it escape well).
A more proper solution would be making temperature spread around in a similar way to smell. Smell spreading mechanics will change soon (will be going 3D), so “proper” heaters and any coolers would also have to be rewritten.
So it is probably going to get in, but not necessarily soon.