It is not hot in the house, but it's really hot outside.

屋子里不热，外面才热呢！

《新英汉大辞典》

It is very hot outside the gym.

健身房外面很热。

youdao

Oh, my goodness! It is so hot outside!

喔！我的天啊！外面真是热死人了！

youdao

And when it is hot outside, they can swim in the outdoor pool.

VOA: special.2009.05.08

We know that when it gets very hot outside or inside, people tend to eat less.

NPR: Study Offers New Insights into Obesity

But the duck that sank last weekend on Lake Hamilton, outside Hot Springs in Arkansas, disappeared in less than a minute.

ECONOMIST: Unsafe waters

It is like putting the hot water heater outside during the summer.

FORBES: Gassing Up: Why America's Future Job Growth Lies In Traditional Energy Industries