The term Finnish sauna by some is considered to be redundant as many traditional sauna bathers will say that the only true saunas are Finnish saunas. Although new technologies have altered the modern sauna and presented numerous benefits over the traditional styles of saunas, many purists refuse the advancements and stick with a classical sauna bath.
Historically, finnish saunas have been around for a considerably long time. It is difficult to set a date as to when finnish saunas were invented as the definition of a sauna is rather vague. Some consider a sauna to be simply a heated room. If that's the case then native american sweat lodges could also be considered saunas. Some definitions require the addition of hot rocks, upon which water is poured to create steam. Whatever your definition, it is important to realize that the sauna has a long and interesting history.
The sauna was invented in Finland, although it has close ties with the Russian banya, the Native American sweat lodge, the Turkish hamam, and the Japanese onsen. Since it's creation it has been a dominant part of the Finnish culture. There are currently more than 2 million saunas (public and private) in Finland, and a population of only 5.2 million people. Unlike what you'd find in North America, over 1.5 million of the 2 million saunas in Finland are in private homes.
Cindos' Finnish & Far Infrared Saunas