Well it's potato and potato begora bejeezus in which you touraloura fields of athenry with the O'Callaghan Naoise Siobhan and then feck and booze and shite and Belfast.
It wasn't Irishness, just...
An airing cupboard? Immersion heater? Brain doing gymnastics trying to figure out how those words would logically interact.
...and then there was Wikipedia.
An airing cupboard is a storage space, sometimes of walk-in dimensions, containing a water heater; either an immersion heater for hot running water or a boiler for central heating water. Shelves, usually slatted to allow for circulation of heat, positioned above or around the heater to provide storage for clothing, typically linen and towelling. The purpose is to allow air to circulate around the stored fabrics to prevent damp forming. A shelf can also be used to fully remove traces of damp from dried clothing before it is put away in drawers and wardrobes. Other names include "boiler cupboard", or (in Ireland) "hot press".
Okay...so it's like shelves around your water heater to dry your clothes. Weird. Is the rest of the house that damp?? I mean, I live in a borderline subtropical climate and we just have plain old shelves, yo. Although the idea of ever-toasty warm towels is appealing.
I think part of it is that in the US, a "cupboard" is...well, for cups. And dishes and such. Clothes go in closets. So we might call that a "water heater closet" or "hot water closet" or something. But then "water closet" has an entirely different connotation in the rest of the world.