- 15 degrees is cold enough to need a sweater and maybe a jacket, unless you're right in the sun

- 20 degrees is enough to take the sweater off, usually, but still cold

- 25 degrees is just starting to warm up, but still uncomfortably cold.

- 30 degrees is a pleasant, comfortable temperature

- 35 degrees is hot enough to turn a fan on

- 40 degrees is hot.

if i was forced to have a window a/c by law, i would set it to 40 degrees, which is when it becomes justified to waste the energy.