Steam shower generator size comes down to one number: the volume of your enclosure in cubic feet, adjusted for the materials and walls that pull heat out of the steam. Measure the room, multiply by the material factor, add allowances for exterior walls and tall ceilings, then choose a generator whose rated volume sits comfortably above your adjusted number. Below is the math, using SteamSpa’s and Delta’s published sizing factors and the ratings printed on the SteamSpa generators we sell.
If you are comparing a steam room with a dry sauna, start with our home sauna buying guide. Dry sauna heaters are sized differently, which we cover in sauna heater size: kW per cubic foot.
Step 1: measure the enclosure in cubic feet
Measure the inside of the finished steam enclosure: length x width x height, in feet. A shower that is 3 ft by 5 ft with an 8 ft ceiling is 120 cubic feet. Include any niche that shares the same air.
Step 2: adjust for material, ceiling height and outside walls
Dense surfaces soak up heat before the room fills with steam, so you size for a larger “adjusted volume” than the room really is. SteamSpa’s online sizing tool lists these material multipliers:
| Wall and ceiling material | SteamSpa multiplier |
|---|---|
| Ceramic tile | x 1.30 |
| Glass tile or glass block | x 1.35 |
| Porcelain tile | x 1.60 |
| Natural stone up to 1/2 in. | x 2.00 |
| Natural stone over 1/2 in. | x 2.25 |
The same tool asks how many exterior walls the room has but does not print a factor for them. Delta’s SteamScape sizing guide does: multiply by 1.1 for one exterior wall and 1.2 for two. Delta also adds 1.15 for a 9 ft ceiling and 1.3 for a 10 ft ceiling, says ceilings should not exceed 8 ft for best performance (10 ft maximum), and recommends the next larger generator if the room has a skylight or outside window. Delta uses its own material factors (1.35 for ceramic, porcelain and glass, 2.0 for stone or marble), so expect small differences between brands. When in doubt, round up.
Neither guide lists a factor for acrylic or prefab steam shower cabins. For those, follow the cabin maker’s generator recommendation.
Step 3: match the adjusted volume to a steam generator kW rating
Every SteamSpa listing in our store prints a “maximum volume rating.” Treat it as a ceiling, not a target: pick a size that leaves some headroom above your adjusted volume. Ratings and power below are per the listings at the time of writing.
| Generator size | Max volume rating | Power (per listing) | Example in our store |
|---|---|---|---|
| 4.5 kW | 75 cu ft | 240V, 19A | Executive 4.5 kW package (EXT450BN-A) |
| 6 kW | 128 cu ft | 240V, 25A | Black Series 6 kW (BKT600ORB-ADP) |
| 7.5 kW | 190 cu ft | 240V, 32A | Black Series 7.5 kW (BKT750ORB-ADP) |
| 9 kW | 255 cu ft | 240V, 38A | Executive 9 kW package (EXT900CH-A) |
| 10.5 kW | 420 cu ft | 240V, 44A | Black Series 10.5 kW (BKT1050CH-ADP) |
| 12 kW | 430 cu ft | 240V, 50A | D-1200 12 kW generator only |
| 2 x 12 kW | 500+ cu ft | 2 x (240V, 50A) | Black Series 2 x 12 kW (BKT2400ORB-ADP) |
Notice the jump from 255 cubic feet at 9 kW to 420 cubic feet at 10.5 kW. If your adjusted volume lands between those numbers, call us before ordering so we can confirm the rating with SteamSpa.
What size steam generator do I need? Worked examples
Small tiled shower, 3 x 5 x 8 ft
120 cu ft x 1.30 (ceramic tile) = 156 cu ft adjusted. That is over the 6 kW rating of 128 and under the 7.5 kW rating of 190, so a 7.5 kW generator fits. Add one exterior wall (x 1.1 per Delta) and you reach about 172 cu ft: still a 7.5 kW, with less headroom.
Porcelain walk-in, 4 x 6 x 8 ft
192 cu ft x 1.60 (porcelain) = 307 cu ft adjusted. That is past the 9 kW rating, so step up to 10.5 kW or 12 kW.
Stone steam room, 5 x 8 x 9 ft
360 cu ft x 2.00 (natural stone) x 1.15 (9 ft ceiling) = about 828 cu ft. That is well beyond any single generator we list. Twin packages such as the 2 x 12 kW are rated for 500+ cu ft, so a room this size needs a conversation with us or SteamSpa before you buy.
Steam generator kW calculator, in one line
Adjusted volume = L x W x H x material factor x wall factor x ceiling factor. Then pick the smallest generator whose maximum volume rating is clearly above that number, and go one size up for a window, skylight or a very cold room. A generator that is too small may never fill the room with steam; one that is much too large draws more current than you need and costs more to wire.
Steam shower electrical requirements
Every SteamSpa generator listing we checked calls for 240V, and current draw rises with size: from 19A at 4.5 kW to 50A at 12 kW, per the listings. Twin packages need two of those circuits. That amperage is the generator’s draw, not a breaker size: your electrician sizes the breaker and wire from the installation manual and local code. Our home sauna electrical requirements guide explains how 240V circuits, breakers and permits work in general.
SteamSpa’s warranty (on its resources page) requires installation by a licensed professional, an inline water filter, filter cartridge changes at least every 6 months, and installation that follows national and local plumbing and electrical codes. It also covers residential use only. Plan for a licensed electrician and plumber from the start.
SteamSpa generator review: what the packages include
We are not going to give you star ratings, but here is what the listings show. The Black Series packages include the QuickStart generator, a WiFi receiver, a Bluetooth touch control panel, steamhead with aroma reservoir, pressure relief valve, two speakers, white and chromatherapy lights and a drain pan. The listings describe steam in about a minute on the smaller units and about 2 minutes on the 10.5 kW and larger ones, plus an auto drain that purges the generator after each session. The Executive packages include the generator, a dual touch pad control panel, steamhead, chromatherapy light, filter and a plumber ready quick connection kit, without the WiFi and speaker extras. The D-1200 is the generator only; its listing notes that it needs a SteamSpa control panel and steamhead to run.
Whatever you choose, the listings recommend adding the Complete Essentials Installation Kit (STMKIT-02), which includes an inline water filter with spare cartridges and a pressure reducing valve. See the full range on our SteamSpa brand page.
A note on health: steam bathing is sold for relaxation, and any wellness claims are the manufacturer’s. If you are pregnant, have heart or blood pressure concerns, or take medication, check with your doctor before using a steam room. For keeping a wet room fresh, our sauna cleaning guide has tips on mold and musty smells that apply to steam rooms too.
Frequently asked questions
What size steam generator do I need for a standard shower?
A 3 x 5 ft tiled shower with an 8 ft ceiling works out to about 156 adjusted cubic feet using SteamSpa’s ceramic tile factor, which points to a 7.5 kW unit (rated 190 cu ft per the listing). Run your own numbers, because stone, extra walls or a taller ceiling change the answer.
Is a bigger steam generator better?
Only up to a point. You want headroom above your adjusted volume, but oversizing adds amperage and wiring cost.
Do steam generators need a dedicated 240V circuit?
Every SteamSpa generator we list is rated for 240V, with draw from 19A to 50A depending on size. Have a licensed electrician size the circuit from the manual and your local code.
Can you help size a steam generator for my room?
Yes. Call us at 866-777-2590, Monday to Friday, 9AM to 6PM PST, with your room dimensions, wall material, ceiling height and number of exterior walls. Orders of $999 or more ship with free freight; below that, freight is a flat $200. Returns follow our return and refund policy.
