The word choice is entirely subjective -- and some people feel heat more strongly than others. Thus, becasue of these two considerations, one person in a room might say, "It's too warm in here," while another in the same room might say, It's too hot in here."
Generally, too, very high temperatures, e.g. water at scalding level, will always be described as "hot."
There is no exact dividing line between saying "warm" or "hot"; but it is understood that the latter is always at a higher temperature relative to the former.
The temperature that you suggest is about 5C (10 degrees Fahrenheit) higher than my office thermostat is set for. I would say that was hot or too hot for the office. If the difference were less (say 26 to 27 C), I might use warm instead.