Is there any difference between 暑い and 熱い?
I saw that both mean 'hot', but I saw that 熱い means hot to touch... The usage of '暑い' is the same as '熱い' or not?

Question

Answer

暑い is (too) hot, talking about the weather.
ex) I want to go out but  it's 38 degrees hot (Celsius) outside. it's 暑い.

熱い is hot , talking about a sensation/generally.
ex) Which do you prefer? Hot coffee or Iced coffee? Hot ,please. It's 熱い.

Answer

The comment by Kaede is well simplified so that you can understand. And let me leave further comments.

1) When you are in fever with somethig, 熱い is only available.
   ex: わたしは日本の着物について熱く語った。
　　　　I told about Kimono in Japan enthusiastically.
         熱い恋に落ちる
        devote to love
        私には日本へ行きたいという熱い思いがあります
　　　 I have a burning desire to go to Japan!
ect...