>>What you call boiler and we call bojler (yep, we borrowed the word - want it back, now that it has a nice j in the middle?) in the US they call water-heater. What they call boiler is the big kettle for house heating. "Boiler room" is where all the heating related stuff, big furnace etc, is installed.
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>Worldwide, and in an engineering sense, the word "boiler" should only refer to systems that turn water into steam, and then distribute the steam (often under considerable temperature and pressure) for heating or power purposes. The term "water heater" is much better for what actually happens in most relatively modern residences and businesses, apart from those that do use steam radiators etc.

Engineering, sense and logic have never stopped any language from going stupid here and there. There are so many things which don't make sense, but stay as they are because... well, I wish I knew why.