[mchannon]

While that's very British, you forget the obvious: The BTU is the British Thermal Unit.

Can't get any more British than something with British in its name. Not to mention it's very widely used in practice, though it's up there with pounds, gallons, and miles.

[Stevvo]

Spoken like a true American. Despite the name, the BTU is an American customary unit, used almost exclusively in America for measuring the power of air conditioners. In practice, it's not quite extinct in the UK as gallons are, but it's on the way.

[kens]

The other weird unit for measuring air conditioning is "tons". One ton of air conditioning has nothing to do with the weight of the air conditioner. Instead, it means the air conditioner provides cooling equivalent to one ton of ice per day. One ton is almost exactly 12,000 BTU/h; curiously, the round number is a coincidence.

[rsynnott]

I think it might be more extinct than gallons, tbh. People still talk about miles per gallon a bit (note that, for extra confusion, a UK gallon isn’t the same as a US one) but _very_ few people would have reason to think about BTUs these days, I’d have thought.