Last Updated: April 2026
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Steam Generator Sizing Guide
Choosing the right steam generator is one of the most important decisions in a steam shower build. An undersized unit will struggle to produce adequate steam; an oversized unit wastes energy and can cause excessive moisture. This guide walks you through exactly how to size your generator.
Step 1: Calculate Your Steam Room's Cubic Footage
Measure the interior dimensions of your steam shower enclosure:
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Length (ft) × Width (ft) × Height (ft) = Cubic Footage
Example: 4 ft × 5 ft × 8 ft = 160 cubic feet
Step 2: Apply Material Multipliers
Different wall materials absorb heat at different rates. Multiply your cubic footage by the appropriate factor:
| Wall/Floor Material |
Multiplier |
| Ceramic or Porcelain Tile |
× 1.0 (baseline) |
| Natural Stone (marble, granite, slate) |
× 1.5 |
| Glass Block Walls |
× 1.25 |
| Acrylic or Fiberglass |
× 0.9 |
| Outdoor or Unheated Space |
× 1.25 |
Example: 160 cu ft × 1.5 (natural stone) = 240 adjusted cubic feet
Step 3: Match Adjusted Cubic Footage to Generator kW
Use this general sizing chart as a starting point. Always refer to the manufacturer's specific coverage specs for the model you're considering.
| Adjusted Cubic Footage |
Recommended Generator Size |
| Up to 100 cu ft |
5–7 kW |
| 100–200 cu ft |
7–9 kW |
| 200–350 cu ft |
9–12 kW |
| 350–500 cu ft |
12–15 kW |
| 500–700 cu ft |
15–18 kW |
| 700–900 cu ft |
18–22 kW |
| 900+ cu ft |
22–26 kW (or dual generator) |
Step 4: Electrical Requirements
Steam generators require a dedicated electrical circuit. Here are the typical requirements by generator size:
| Generator Size |
Voltage |
Amperage |
Circuit |
| 5–9 kW |
240V |
30–40A |
Single phase |
| 10–15 kW |
240V |
50–60A |
Single phase |
| 16–22 kW |
240V |
60–80A |
Single phase |
| 26 kW (dual) |
240V |
80A per generator |
Two dedicated circuits |
Always consult a licensed electrician before installation. Electrical requirements vary by model — confirm with the manufacturer spec sheet.
Step 5: Don't Forget the Control Kit
Most steam generators require a separate control kit (sold separately). The control kit includes the user interface panel, temperature sensor, and steam head. Make sure the control kit is compatible with your generator model before purchasing.
For Kohler Invigoration Series generators, the compatible control kits are sold separately — browse our steam generator accessories to find the right match.
Additional Sizing Considerations
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Ceiling height over 8 ft: Add the extra volume to your calculation — steam rises and a taller room requires more output.
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Exterior walls or cold climates: Apply an additional 1.1–1.25× multiplier for rooms on exterior walls or in cold climates.
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Multiple steam heads: If your design calls for more than one steam head, size up accordingly.
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Ventilation: Ensure your steam shower is properly sealed. Gaps or poor sealing dramatically reduce efficiency.
Shop Steam Generators by Size
Browse our full selection of residential steam generators, including the Kohler Invigoration 2.0 series:
Not sure which model is right for your project? Contact our team — we're happy to help you spec the right generator for your steam shower build.
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Disclaimer: The wellness benefits described in this guide are for general informational purposes only and are not intended as medical advice. These statements have not been evaluated by the Food and Drug Administration. Prime Regeneration products are not intended to diagnose, treat, cure, or prevent any disease or medical condition. Consult a qualified healthcare professional before beginning any new wellness practice, particularly if you have a pre-existing health condition.
