The short answer
Multiply finished inside width × depth × height. Choose the smallest current generator whose maximum volume is at least that result. Kohler recommends an 8-foot-or-lower ceiling; for each foot above 8 feet, move to the next generator size without disregarding the selected model's published volume limit. Kohler selection guide, form 22-3187-0824 (official Kohler source)
SteamDesignPro treats any partial foot above 8 feet conservatively as a started additional foot and flags it for professional confirmation. That rounding treatment is this independent planner's cautious interpretation; the manufacturer document says “for each foot above 8 feet.” Use Kohler's current calculator and project-specific documentation to confirm the final selection. Kohler steam calculator (official Kohler source)
The current generator installation instructions reviewed for the K-323xx families identify 10 feet as the maximum ceiling height. A design above 10 feet is therefore outside the documented range used by this planner and requires manufacturer review. Kohler 5–11 kW instructions 1601844-2-B (official Kohler source) Kohler 13–15 kW instructions 1601845-2-B (official Kohler source)
Current K-323xx model sequence
| Model | Configuration | Power | Maximum room volume | Published dedicated service |
|---|---|---|---|---|
| K-32324-NA | Single | 5 kW | 84 cu ft | 1 × 240 V / 40 A |
| K-32325-NA | Single | 7 kW | 112 cu ft | 1 × 240 V / 50 A |
| K-32326-NA | Single | 9 kW | 240 cu ft | 1 × 240 V / 60 A |
| K-32327-NA | Single | 11 kW | 317 cu ft | 1 × 240 V / 60 A |
| K-32328-NA | Single | 13 kW | 447 cu ft | 1 × 240 V / 80 A |
| K-32329-NA | Single | 15 kW | 500 cu ft | 1 × 240 V / 90 A |
| K-32332-NA | Tandem | 18 kW | 550 cu ft | 2 × 240 V / 60 A |
| K-32333-NA | Tandem | 22 kW | 634 cu ft | 2 × 240 V / 60 A |
| K-32334-NA | Tandem | 26 kW | 894 cu ft | 2 × 240 V / 80 A |
| K-32335-NA | Tandem | 30 kW | 1,000 cu ft | 2 × 240 V / 90 A |
Table source: Kohler “Select Your Controller and Steam Head,” form 22-3187-0824 (official Kohler source). The electrical values shown for tandem models are per circuit; the source requires two dedicated circuits.
A repeatable five-step method
Use finished inside dimensions
Measure the steam-containing volume at the completed wall, floor, and ceiling planes. Convert all three dimensions to one unit system before multiplying.
Calculate actual base volume
In US units, width (ft) × depth (ft) × height (ft) gives cubic feet. Do not substitute floor area for volume.
Select by the first capacity boundary that covers the room
A result exactly on a published maximum remains within that boundary. A result even slightly above it moves to the next model: for example, 112 cu ft fits K-32325-NA, while 112.1 cu ft moves to K-32326-NA before ceiling adjustment.
Apply the ceiling-height sequence step
At or below 8 feet, there is no extra step. Above 8 feet, SteamDesignPro advances one model for every started foot as a conservative planning treatment. It never uses that step to select a model whose published maximum is below the actual room volume.
Stop when the published range stops
A room over 1,000 cu ft, a ceiling above the documented 10-foot maximum, or a ceiling adjustment that would move beyond K-32335-NA is outside this method. The planner reports “manufacturer review required” instead of extrapolating a larger system.
Boundary examples
Exactly at a published limit
4 ft × 3.5 ft × 8 ft = 112 cu ft. With no above-8-foot step, the preliminary selection is K-32325-NA, 7 kW.
Just over a limit
4 ft × 3.51 ft × 8 ft = 112.32 cu ft. That exceeds 112 cu ft, so the preliminary base selection moves to K-32326-NA, 9 kW.
Partial foot above 8 feet
5 ft × 4 ft × 8.5 ft = 170 cu ft. Volume first points to K-32326-NA; the planner's conservative started-foot treatment advances the preliminary selection to K-32327-NA and flags the interpretation for confirmation.
Outside the documented range
A room above 1,000 cu ft or a ceiling above the documented 10-foot maximum receives no model recommendation from this sequence. Contact Kohler and the responsible design professionals.
Capacity boundaries and the manufacturer's 8-foot ceiling note: official selection guide (official Kohler source).
What changes with a tandem selection
The four tandem SKUs represent paired-generator systems. Kohler's selection guide requires two dedicated circuits and two drain pans, and its control chart requires two steam heads for tandem generators. Kohler tandem requirements (official Kohler source)
Consequently, the jump from a 15 kW single system to an 18 kW tandem system changes more than capacity. It affects equipment count, branch circuits, steam outlets, drainage planning, space, access, and control compatibility. Those consequences should be reviewed before treating the model number as final.
Electrical wording that needs professional review
Manufacturer instruction and local code must be reconciled
Kohler's published guide calls for a separate dedicated 240 V circuit and says no GFCI should be connected to the circuit. See the manufacturer note (official Kohler source). SteamDesignPro repeats that wording only as a sourced manufacturer requirement. It is not electrical design advice and does not override adopted code, a permit authority, or the licensed electrician responsible for the installation.
Questions the calculation does not settle
- Does tile, stone, or glass change this published table?
- The current Kohler selection procedure cited here does not publish a surface-material multiplier. SteamDesignPro records material as a construction input but does not silently alter generator capacity.
- Can the generator be more than 25 feet from the steam head?
- Kohler says it needs to be installed within 25 feet. The planner flags a longer entered distance instead of assuming equivalent performance. Manufacturer distance note (official Kohler source)
- Is the capacity table an electrical design?
- No. It reports manufacturer nameplate planning values. A licensed electrician must design the installation and confirm every applicable requirement.
Continue with the planning guide, prepare the project checklist, or inspect the official-source register.