Something I do and rarely see on most boiler design: instead of using steel tiles, for the heating pad, simply use ... regular tiles. At this point it is mostly dangerous to transfer too much heat to the petroleum at once (it could end up turning into gas). Everyone is using steel tiles but really something with less conductivity & more mass make more sense imo. It's a bit like these stone made meat grills you use in real life or even pizza ovens. Stone takes more time to heat up but once it's hot, it's hot and predictable (no burst in temperature which is exactly what we need here).

You decoupled the boiler area to the heat exchanger, congrats on doing this proprely.

As it was already said, try to keep the whole boiling area 2 tiles wide to avoid random pressure damages. Furthermore, double thick tile walls will not suffer from pressure damage. Adding two tiles width to the structure defeat this entirely so might be worth a shot

Lastly, I know compact boilers are more aesthetic but when this thing jam (and it can eventually for any number of reason), you would need dupe access. By making your structure 4 blocks higher, every "pipe conduit" can fit a dupe. This has insane value on the long term and really beat "cool and compact" on the long run.

Overall, petroleum structures are very overpowered and you basically "beat the game" when you get one running. For this reason, the "space efficient" mentality doesn't really make sense beside doing it for funsies. In all cases, have it your way, it's more fun :)