But that doesn’t seem fair either? GP is perfectly happy at a cooler temperature.

If GP actually preferred an even colder temperature (perhaps for sleeping or exercising) and had to turn on the air conditioner, can they bill their neighbors? GP must pay more for their neighbor’s comfort.

But then the neighbours would both pay them and turn up their own heating to keep their own house at their own favourite temperature, since the airco is working against that.

Correct, it's potential that they are paying for GP's discomfort at times