You would simply use the future tense or use the auxiliary aller with infinitive construction. In your example, to say, “we will be hot,” we would say “nous aurons chaud” or “nous allons avoir chaud.”

This also extends to other constructions with avoir. Some other examples from the internet:

• avoir soif/faim: Après un jeûne de Yom Kippour, vous aurez souvent plus soif que faim. (After fasting for Yom Kippur, you will generally be more thirsty than hungry.)

• avoir tort: Vous aurez tort de rater [tel ou tel évènement]. (You will be wrong to miss [such or such an event].)

• avoir honte: Vous aurez honte devant l’histoire. (You will be ashamed in the eyes of history.)

• avoir froid: Nous allons avoir froid. (We will be cold.)