I'm surprised at some of the answers too. He said he it going to run it
when there are no clothes in the dryer, just using it as a heater. Won't be
any humidity from it that way.

Yes, that was exactly my point. It is clear that one could save
heating money by venting the dryer into the house while drying your
clothes (which had not been noted). It is not clear (and, actually,
pretty unlikely) that you would if just using it as a standalone
heater without it drying clothes. Part of my point was that, to some
degree, humid air could be advantageous.