No! - You are not being foolish;
Yes! - You can still get a great bathing experience in a 3'x3'x6'; and
Yes - The size of the room can certainly enhance the experience
While there are 'comfort' advantages to having a larger shower area, the many physical, mental, and emotional benefits know no room size.
But there is no reason you can't have it all! Consider purchasing a dual kilowatt generator, which can be used at a lower kilowatt now and then switched higher when you increase your room size, or one where the heating element can be upgraded to a larger size. These features are available among the industry leading steam bath generator manufacturers and your choices would be determined by how large you plan to increase your room size. Call a Steam Bath Specialist
to help you select the right equipment for your project.
You KNOW you're going to thank yourself every time you steam bathe.