How i can graph in 3 dimension, dependent of the temperature?

Good day for everyone, i have a simple question. I have matlab R2019a. My question is..

How i can graph this equation:

T = - 3 (x^2+y^2+z^2)^(1/2) + 300

is a room that is dependent of temperature in all directions

I tried this, but doesn't appear the graph

 syms x y z
 T0 = 300
 f = -3*sqrt((x^2+y^2+z^2))+ T0;
 fimplicit3(f, [0 0 0])

Thank you so much for your valious time.