I have something similar to Economy 7 whereby overnight rates are cheaper. My vented cylinder has 2 immersions, the top one is NOT at the cheap rate, it's just for 'emergency' use. For reasons I won't bore you with, I may need to change to a pressurised cylinder. I can't be certain from the sites I've visited - do unvented tanks come with 2 immersions and the extra insulation that Economy 7 tanks usually have? Many thanks.