Well, I for one agree with you, Pablo. Generally we talk of "hot" showers and drinks, at least in BrE. And in many contexts where "cald" is being translated in this course as "warm". I'd in fact say "hot".
It seems to me that there is obviously a different crossover point between "cald/fierbinte" and "warm/hot".
I agree - I have repeatedly missed questions for translating "cald" as "hot". My understanding of "fierbinte" is more like "boiling hot", and it seemed to be mostly used to describe the temperature of food/drinks. I don't recall, for example, the temperature outside ever being described as "fierbinte" even when it was nearly 40C. That definitely qualifies as "hot" in English!
Yes you are right. Use " fierbinte" when using the tactile sense, when you can decide if you want to touch something or not...food, water, drinks and orher things around you that you want to determine if they are hot= fierbinte or just warm= cald, but for air temperature, because the air is touching you, you can not control that you have to say "cald" or "foarte cald"...you go outside or in a sauna for example, and it is hot=cald, or very hot= foarte cald...never fierbinte. " It is very hot in the sauna"= "este foarte cald în saună" , but if you touch the charcoal or the rocks inside the sauna...those are "foarte fierbinți"( plural)..sometimes even " super fierbinți".
In our sentence" duşul este foarte cald" it means that is pleasantly hot/ nicely warm ( some people love to take hot showers) , if it was (burning) hot it would be " (foarte) fierbinte". In Romanian for water=apă, use " lukewarm = călduță/călîie" ( read î like â), warm= caldă, very warm( almost hot)= foarte caldă, hot= fierbinte, very hot( burning or boiling hot) = foarte fierbinte.