About half of buyers pick the wrong size. Too small and you wait forever for steam; too big and it short-cycles, leaving you hot with no steam. Here's how to nail it.
Enter your shower dimensions and wall material. We'll estimate the adjusted cubic feet and the right kW. Always round up — undersizing is the costlier mistake.
This gives you a strong estimate. For a guaranteed spec, call us — sizing help is always free.
Charts that only ask for square footage get people wrong all the time. Four factors matter.
Length × Width × Ceiling Height, in feet. Don't subtract for benches — they still absorb heat.
Tile is the baseline. Natural stone and marble roughly double the load because they soak up heat before the room warms.
Generators assume ~8 ft. For every foot above, step up a size — steam rises, so tall ceilings need more power (or a fan).
| Adjusted cubic feet | Recommended kW | Typical shower |
|---|---|---|
| Up to 90 | 6 kW | Small tiled enclosure (≈ 3 × 4 × 7.5 ft) |
| 91 – 135 | 7.5 – 9 kW | Mid-size tile shower |
| 136 – 180 | 10 – 12 kW | Large tile or medium stone shower |
| 181 – 225 | 12 – 15 kW | Full marble enclosure / large custom |
| 226 – 315 | 15 – 18 kW | Oversized luxury shower, heavy glass |
Rule of thumb: about 1 kW per 45–50 adjusted cubic feet. When you're between sizes, round up.
The generator runs flat-out and still can't keep up. You get long cold gaps between steam and it wears out fast from constant max-output stress.
It short-cycles — blasts steam, hits the thermostat, shuts off. You're left in a hot room with no steam, then it repeats. Bigger is not "safer."
No. Benches, seats and niches still absorb and radiate heat, so leave them in your cubic-foot calculation.
Step up one generator size per foot above 8 ft, and add a marine-grade fan near the ceiling to push heat down. Otherwise the heat pools up high while your feet stay cold.
Dense materials like marble, granite and slate are thermal sponges — they absorb a lot of heat before the room reaches temperature. Stone roughly doubles your effective room size for sizing.
Round up, within reason. A slightly larger unit runs shorter cycles and lasts longer. Just don't massively oversize, or it short-cycles. When in doubt, call us.
Tell us your dimensions and wall material — we'll confirm the exact model and kW, and quote you the best price.