Finland might be rich in global standard in like other western country but most people are middle class and generally lower wealth than some other European countries. they still use saunas.

Time-wise, it takes 1-2h to heat up a sauna. You can have one that the heater is insulated and has a top so it can be always on. Then you just remove the top and sauna is ready in 15mins. If you are working class, you still have time to a sauna in evening.

Now the main problem is the electricity cost. Many have wood heated saunas in the contryside or at their family’s summer cottage where you get the wood for free from your own forest.

> Noncausal mechanisms, including socioeconomic status and reverse causation bias, have been proposed as contributors to the KIHD findings (Kivimaki et al., 2015). Although differences in socioeconomic status may influence sauna access and opportunities for use, the robust dose-dependent associations observed between sauna bathing and sudden cardiac death, coronary artery disease, and cardiovascular events in the KIHD studies are indicative of genuine inverse associations (Laukkanen et al., 2015a). Furthermore, the KIHD studies were conducted in Finland, where sauna use is deeply rooted in the culture, and saunas are readily accessible (Laukkanen et al., 2015a). Similarly, whereas reverse causation bias figures prominently in observational studies and is a valid concern when investigating links between cardiovascular disease and lifestyle, the KIHD findings were adjusted for potential biases, including lifestyle factors such as socioeconomic status, physical activity, and cardiorespiratory fitness (Laukkanen et al., 2015a).

A sauna is just a room/building with a heater that (usually) has a load of stones in it and some (high up) benches. That's it, that's a sauna.