The correct steam generator size for your room is found using a number of factors. The “correct” size is that the generator has enough output so that in a reasonable time, typically five minutes or less, the room is ready for use. Even the smallest generator will heat a large room, but it will take an unreasonably long time to do it, so sizing is important. The elements are, room cubic volume, wall finish and ceiling height.
You can determine your room’s cubic volume by multiplying length by width by height. If your room is 6 x 5 x 7.5 feet, it’s cubic volume is 225 cubic feet. Using this number as a base, you multiply it by either 1.3 or 2 depending on the room’s finish. If the common ceramic tile or similar, 1.3 and a natural stone such as marble, 2.
Natural stone absorbs a lot of heat so a marble room will take longer to heat to the desired temperature than a ceramic tile. If your room has a higher than average ceiling, such as 8 feet or higher, since heat rises change the multiplication factor to 1.5 and 2.2.
To save you time, here is a simple chart that will show the correct generator kW requirements. It is always better to size up, rather than down as the room temperature will be reached faster and easily maintained using the automatic temperature control.
| Room cubic volume | Ceramic Tile, kW size | Natural Stone, kW size | High ceilings/winter outside walls |
| up to 150 | 6 kW | 8 kW | 8 kW |
| up to 200 | 8 kW | 9 kW | 10.5 kW |
| up to 250 | 9 kW | 10.5 kW | 12 kW |
| up to 300 | 9 kW | 12 kW | 12 kW |
| up to 350 | 10.5 kW | 12 kW | 12 kW |
| up to 400 | 10.5 kW | 12 kW | 24 kW |
| up to 450 | 10.5 kW | 24 kW | 24 kW |
| up to 500 | 12 kW | 24 kW | 24 kW |
| up to 550 | 24 kW | 24 kW | 24 kW |
| up to 600 | 24 kW | 24 kW | 24 kW |