Natural convection in a cavity description

Dear colleagues,

I would like to kindly ask for advice about natural convection description in Comsol.

Namely, I have a cavity filled with Argon at initial temperature of 0 degC. One of its surfaces (say, left one) is at fixed 40 degC temperature. I need to simulate the opposite (right) surface temperature dynamics.

I used Comsol model similar to "Free Convection in a Water Glass".
(www.comsol.com/model/free-convection-in-a-water-glass-195)

I'm not sure, if convection should be described only by Volume force (gravity), or should I also use "Internal convection" on that "opposite" surface?

Thanks in advance!