I really don't like high heat training, ie, deliberately looking for hot environments or making your indoor training hot (slow fan, etc).
It forces you to scale back your efforts and that's not good for building strength and speed. It might be detrimental to your high or top end power.
I prefer instead to "overheat" myself simply by doing hard intervals z4 to z5 for more than 30 minutes continuously. My quick dry shirt would be dripping wet even with strong fan if I did that