What heat measures
Margin used against account value tells you how much of your capital is currently committed and how much cushion remains for adverse moves. Low heat means most of the account is idle; high heat means small adverse moves matter across several sleeves at once.
It is not a forecast and not a risk score. It is a snapshot of commitment, and it is the fastest way to notice that a basket has quietly become concentrated in time even when it is diversified by leader.