If you are trying to father a child,
you may want to avoid hot baths as
they are known to decrease sperm production.
If this is not a concern, then I would say
that as long as the water isn’t ridiculously
hot (i.e. so much so that your body needs
to exhaust qi to protect itself and guard
against the trauma), then I don’t think it
is a problem.
In particular, if the water is hot but
comfortable, it can relax the muscles in
your body . . . in particular, the psoas
muscles in your lower back, and consequently
open your door of life. The kidneys work
hardest when cold, so the heated water will
relax them and let them rest a bit.
Since hot (but comfortable) water can also
be detoxifying (basic principle behind
going to the Hot Springs or soaking in a
clay bath etc. etc.), it can actually be good
But like anything, you don’t want to overdo it,
or take the temperature so hot that it becomes
uncomfortable (because then your body exhausts
its reserves trying to protect itself).