2 toroidal transformers mounted atop one another?

I plan on running two toroids of the same size for a power supply.
Stacking one atop the other laying flat shouldnt be a problem should
it? I'm wondering if the two different windings in close proximity will
interfere with one another. If they need to be separated, how far
should they be kept apart? I plan on spacing them like 1/2" to allow
air flow and cooling between them and under the bottom one.

Thanks Ron