The steam shower generator is the component that decides whether the room works, and the one most often chosen by price. Sizing is not simply enclosure volume: the surfaces in the room change the answer, and a unit specified on raw cubic feet in a stone lined shower will never reach temperature.
Sizing starts with volume, then adjusts
Every maker publishes a table of kilowatt rating against enclosure volume. Then you adjust upward, sometimes substantially, for surfaces that pull heat away: natural stone, thick porcelain, glass block, an exterior wall, or a ceiling above the standard height. Makers publish these multipliers and they exist because ignoring them is the common failure.
Where it goes
Outside the wet area, within the maker's maximum pipe run to the steam head, in a space that stays above freezing and that you can actually open. A vanity cabinet, a linen closet or a conditioned attic are typical. Burying one behind finished tile saves a cupboard and guarantees nobody ever services it.
Scale is what kills them
Boiling water leaves minerals behind, and in hard water areas that scale is the main cause of early failure. An auto flush that drains the tank after each use is the feature worth paying for. Where water is very hard, a softener or an inline treatment on the feed extends the unit's life more than any other single measure.
The electrical
Generators are wired to a dedicated circuit sized to the rating, and the bigger units need a substantial one. That is an electrician and possibly panel capacity, so confirm it before choosing a size. An undersized circuit is not a matter of slower heating: the unit will trip, and repeated tripping damages both the breaker and the generator.
Questions people ask about steam shower generator
How do I size a steam generator?
Start from the enclosure volume in the maker's table, then apply their multipliers for stone, glass, exterior walls and high ceilings. Undersizing cannot be fixed later.
Where should it be installed?
Outside the wet area, within the maker's pipe distance, frost free and reachable. Service access matters as much as distance.
What makes a generator fail early?
Scale, in almost every case. An auto flush and, in hard water, treatment on the feed are what extend its life.