The steam shower enclosure is the component that decides whether the room works, because a generator can only heat the volume it is allowed to keep. An ordinary shower screen that stops short of the ceiling will send your steam into the bathroom and your money with it, and no amount of generator fixes it.
Sealed to the ceiling, not to head height
A steam enclosure runs floor to ceiling, glazed or tiled all the way, with a transom panel above the door if the door itself is standard height. Every joint is sealed. The usual failure is a lovely frameless screen that stops at seven feet, which is correct for a shower and useless for steam.
The door
It seals on all four edges including the top, swings outward, and needs a magnetic or friction catch rather than a latch. Gaskets are part of the specification and they are a wear item, so check they are replaceable. A door that fits well is the difference between a five minute warm-up and a room that never quite arrives.
The ceiling
Sloped by a couple of degrees toward a wall so condensate runs rather than drips, and finished in something that sheds water. A flat ceiling in a steam enclosure rains on the occupant, and it is the complaint that comes first in a conversion where the ceiling was left as it was.
Materials and the vent
Tile or stone over a waterproofed substrate, tempered safety glass, and marine grade or well sealed hardware, because everything in there lives wet and hot. Fit a bathroom extract outside the enclosure so the room can dry between sessions, and leave the enclosure door open afterwards: an enclosure that never dries is the one that grows mold.
Questions people ask about steam shower enclosure
Can a standard shower screen work?
No. A steam enclosure runs to the ceiling with a sealed transom and door. A screen that stops at head height lets the steam straight out.
Does the door need a special seal?
Yes, on all four edges including the top, and the gaskets should be replaceable because they wear.
Why does the ceiling need a slope?
So condensate runs to a wall instead of dripping on you. A flat ceiling in a steam room rains.