Ter calor vs. estar com calor
In Portuguese, expressing physical sensations like temperature implies that a person experiences the feeling rather than becoming it. Therefore, you do not use the verb ser (to be permanently), but rather constructions implying possession or a temporary state. Both ter calor and estar com calor mean to feel hot, but they use different grammatical logic and are often preferred in different regions.
Ter calor
A1This phrase literally translates to to have heat. It uses the verb ter (to have). It is the most classical construction for physical sensations (hunger, thirst, cold) and is the standard form used in European Portuguese (Portugal) and African Portuguese-speaking countries.
Eu tenho muito calor nesta sala pequena.
(I am very hot in this small room.)
Se tiveres calor, podes abrir a janela.
(If you are hot, you can open the window.)
As crianças têm calor quando correm no parque.
(The children get hot when they run in the park.)
Ontem à noite eu tive tanto calor que não consegui dormir.
(Last night I was so hot that I could not sleep.)
Estar com calor
A1This phrase literally translates to to be with heat. It uses the verb estar (used for temporary states) combined with the preposition com (with). While understood universally, this is the dominant form used in Brazilian Portuguese.
Estou com calor, vou ligar o ar condicionado.
(I am hot, I am going to turn on the air conditioner.)
Você está com calor ou está confortável?
(Are you hot or are you comfortable?)
Nós estávamos com calor esperando o ônibus.
(We were hot waiting for the bus.)
Meu cachorro parece estar com calor.
(My dog seems to be hot.)
Summary
Both ter calor and estar com calor describe exactly the same sensation of feeling high temperature. The difference is synonymous with the difference between saying I have heat vs I am with heat. In practice, use ter calor if you are targeting European Portuguese usage, and estar com calor if you are targeting Brazilian Portuguese usage.