Tengo calor es correcto.

Tengo calor, to be in Spanish (ser) is used only to define yourself about some stable aspect, I'm tall / soy alto, I'm clever / soy inteligente... Instead feelings generated by something, like your to feel hot, are seen like something "you have" in that moment, so in Spanish you will say like "I have hot" / tengo calor.

Tengo calor :)

Tengo calor