So you're ready to add steam to your bathroom — but now you're facing the most technical part of the project: picking the right generator. Sizing a steam shower isn't just about square footage. It's about cubic volume, ceiling height, and wall material. Get it wrong and your generator will either struggle to fill the space or cycle off before you've had time to relax.
At TheSteamStore.com, we carry the three leading residential steam brands: Mr. Steam, ThermaSol, and Amerec. Each brand has its own sizing formula. This guide walks through all three so you can find the right fit for your shower.
Prefer to skip the math? Use our Steam Shower Sizing Calculator — enter your dimensions and wall material and it will recommend the right model automatically.
Step 1: Calculate Your Base Room Volume
Start with the same calculation for every brand. Measure the interior dimensions of your shower enclosure in feet and multiply:
Length × Width × Height = Cubic Feet
For example: a 4 ft × 5 ft × 8 ft shower = 160 cubic feet. That's your starting number. From here, each brand applies its own adjustments for wall material and ceiling height.
Mr. Steam: MS, Super, & MX Series Sizing
Mr. Steam calls this the Total Adjusted Room Volume. Apply the following multipliers to your base cubic footage before selecting a model:
- Ceramic or porcelain tile on cement board or mortar bed: no adjustment
- Natural stone (marble, stone, shale, glass block, concrete): multiply by 1.5
- Acrylic: multiply by 0.6
- Ceiling higher than 8 ft up to 9 ft: multiply adjusted volume by 1.15
- Ceiling higher than 9 ft up to 10 ft: multiply adjusted volume by 1.3
Mr. Steam sizing example: 4 × 5 × 8 ft tile shower = 160 cu ft. No adjustment for tile, no adjustment for 8 ft ceiling. Total adjusted volume = 160 cu ft → MS225R (7.5 kW). Same shower in natural stone: 160 × 1.5 = 240 cu ft → MS400R (9 kW).
| Adjusted Volume (cu ft) | Model | kW |
|---|---|---|
| 0 – 71 | MS90R | 5 |
| 72 – 107 | MS150R | 6 |
| 108 – 161 | MS225R | 7.5 |
| 162 – 257 | MS400R | 9 |
| 258 – 339 | MSSUPER1R | 10 |
| 340 – 411 | MSSUPER2R | 12 |
| 412 – 482 | MSSUPER3R | 15 |
| 483 – 678 | MX4R | 20 |
| 679 – 822 | MX5R | 24 |
| 823 – 964 | MX6R | 30 |
ThermaSol: ProIII Series Sizing
ThermaSol's approach is different from Mr. Steam and Amerec in one important way: wall material does not affect generator selection. ThermaSol's engineering accounts for material variations internally, so you size purely on cubic footage — with one exception: ceiling height. The ProIII generator can be installed up to 50 feet from the shower in any finished, climate-controlled space with 6 inches of clearance on all sides.
- Up to 8 ft ceiling: use base cubic footage as-is
- 9 ft ceiling: go up 1 generator size
- 10 ft ceiling: go up 2 generator sizes
- Over 10 ft: call us for specialized sizing — contact us here
| Shower Volume (cu ft) | PROIII Model |
|---|---|
| Up to 84 | PROIII-84 |
| 85 – 140 | PROIII-140 |
| 141 – 240 | PROIII-240 |
| 241 – 395 | PROIII-395 |
| 396 – 575 | PROIII-575 |
| 576 – 750 | PROIII-750 |
| 751 – 1200 | PROIII-1200 |
Amerec: AK Series Sizing
Amerec's sizing focuses on material density. For tile or non-porous surfaces, use your base cubic footage directly. For natural stone (marble, granite, slate, travertine), multiply your cubic footage by 1.75 before selecting a model.
Amerec sizing example: 4 × 5 × 8 ft tile shower = 160 cu ft → AK9 (150–300 cu ft range). Same shower in natural stone: 160 × 1.75 = 280 cu ft → still AK9. A larger 5 × 7 × 8 ft shower in natural stone: base volume 280 cu ft × 1.75 = 490 cu ft → AK14 (350–550 cu ft range).
| Model | Volume Range (cu ft) | kW |
|---|---|---|
| AK4.5 | 60 – 90 | 4.5 |
| AK6 | 80 – 150 | 6 |
| AK7.5 | 100 – 200 | 7.5 |
| AK9 | 150 – 300 | 9 |
| AK11 | 200 – 400 | 11 |
| AK14 | 350 – 550 | 14 |
Amerec steamhead placement: Mount the ComfortFlo steamhead 18" above the floor (or 6" above the rim of a bathtub), as far from the seating area as possible. AK4.5 through AK11 require 1 steamhead; AK14 requires 2.
Quick Select Comparison: All Three Brands
Tile walls, standard 8 ft ceiling. Apply material and ceiling adjustments before using this table if your shower differs.
| Base Volume | ThermaSol | Mr. Steam | Amerec |
|---|---|---|---|
| ~80 cu ft | PROIII-84 | MS150R | AK4.5 / AK6 |
| ~150 cu ft | PROIII-240 | MS225R | AK7.5 / AK9 |
| ~350 cu ft | PROIII-395 | MSSUPER2R | AK11 / AK14 |
| ~550 cu ft | PROIII-575 | MX4R | AK14 |
Frequently Asked Questions
Does wall material really make a difference?
Yes — for Mr. Steam and Amerec. Natural stone is porous and absorbs heat, requiring a more powerful generator. Acrylic retains heat well and can use a smaller unit. ThermaSol is unique in that its sizing accounts for materials internally, so you size on cubic footage alone regardless of wall type.
What if my shower has a ceiling higher than 8 ft?
Steam rises, so taller ceilings mean more volume to heat and a less efficient steam environment at bather level. For Mr. Steam, multiply your adjusted volume by 1.15 for ceilings over 8 ft up to 9 ft, or by 1.3 for ceilings over 9 ft up to 10 ft. For ThermaSol, go up one or two generator sizes. Amerec recommends a maximum ceiling height of 8 ft for best performance, though higher ceilings work — they just increase the cubic footage you are sizing against. Ceilings above 10 ft require a custom sizing conversation — contact us directly.
Should I size up if I'm between two models?
Always. An undersized generator will run continuously and struggle to reach temperature. An oversized generator will reach temperature faster and cycle less frequently. When in doubt, go up one size.
Which brand is easiest to size?
ThermaSol is the most straightforward — tile, stone, acrylic, it doesn't matter. You measure your cubic footage, check the table, and you're done. Mr. Steam and Amerec both require material adjustments but their formulas are clearly documented and easy to follow.
How do I protect my generator once it's installed?
Hard water is the biggest threat to generator longevity. Mineral scale builds up on heating elements over time and reduces efficiency. The best prevention is an automatic flush system installed at the same time as the generator. Read our full guide: Hard Water & Steam Generators: How to Protect Your Investment.
Why Order from TheSteamStore.com?
- Exact Sizing Help: Not sure about your measurements? Call or email us!
- Free Shipping: Steam generators ship free within the contiguous United States on orders over $199.
- All Three Brands in One Place: Compare Mr. Steam, ThermaSol, and Amerec side by side without visiting multiple sites.
Ready to find your generator? Use our Steam Shower Sizing Calculator for an instant recommendation, or browse our Mr. Steam, ThermaSol, and Amerec collections at TheSteamStore.com today.