What do you mean by hot?
Why 18 numbers? If you are looking to cover half the wheel then why not just go EC?
What you will find is that for example tracking the last 100 spins, is a handful of numbers will appear 3+ times, a handful will not appear at all and the majority will appear twice, how do you separate them out into the hottest 18?
To get a clearer list of 18 hot numbers you will need to track a large number of spins, but who wants to sit around tracking them.
If you explain your purpose of why you need the hottest 18 I might be able offer something else.