Space heater question

Hope this ok here. I have a small area that I've turned into a little snake closet basically (open front). I have a small oil filled heater in there for holding ambient temps, got it used but have been using for awhile no issues. Im planning on adding another rack and having a shelf built for them to sit on with heater below.
Now my question- how much space should I leave around the heater/wood?

You may just want to go online and see what the manufacturer's recommendations are for that. Some of these units need a minimum amount of space around them. It is not just a matter of temperatures, but a matter of safety.

For some reason didn't even think to google for a manual with getting it used. Lol. Thanks!