Our Kohler steam setup (circa 2006) simply has a small dimple on the top of the steam port. One simply places a few drops of the aroma oil in the dimple and heat from the steam releases it into the air. Simple, inexpensive.

My thermasol has the same setup as formula. Works great, no extra controls needed

My Serene Steam, which is sold here on Houzz, is a specially designed aromatherapy steam spa that has an inlet for essential oils, which are then distributed into the steamy mist. It's unique in that it doesn't use electricity to generate steam. The lung health institutes website recommends these 5 essential oils to help people with lung issues like COPD; Eucalyptus, Lavender, Myrrh, Frankincense, & Bergamot. And of course only use high quality oils such as Paradise Springs and Doterra, the latter of which many are food grade.

the white tile in my steam shower, around the steam port, suddenly have large yellowish/brown stains that I can't seem to remove. The stains appeared after my cleaning sprayed a 1:1 bleach to water solution in the shower for general cleaning. I'm wondering if the stains have anything to do with using essential oils. Perhaps they've reacted with the bleach. Has anyone else heard of this?

Referring to your comment about stains Mike...Do you have an electric generator type that uses a small nozzle to disburse the steam? If so, maybe someone spilled oil on the walls when filling it? Or do you have stone or marble tiles which are porous, as opposed to ceramic or porcelain tiles? In contrast I have a Serene Steam which mixes the oils diretly into the hot steamy forced air mist, and don't see how it could happen with that type of output.