Infrared heaters and the sauna
I have no first hand experience with infrared (IR) heaters in saunas. Since my expertise and bias lies with the Finnish sauna, take the following with a grain of salt.
How do IR saunas work?
The traditional sauna heater uses a large amount of stones to store heat during the sauna bathing. Heating of course takes a long time since the stones must first absorb an important amount of energy. Throwing water on the stones in a traditional sauna brings up the moisture in the room, momentarily making you feel hotter since steam carries energy better than air.
In an IR sauna a far infrared radiator sends energy directly to the skin of the bather in the form of heat waves (infrared electromagnetic radiation, essentially the same kind of radiated heat we get from the sun or a hot lightbulb). This energy penetrates the skin several millimeters (up to some centimeters?), and reacts with the skin's tissues, increasing its temperature and quickly inducing sweating.
In the traditional Finnish sauna, heat energy is transferred both by radiation, conduction and convection (from the heater's stones and the room's walls, from the löyly and from the airflow, respectively). Heat from an IR radiator behaves much like light from a lightbulb - it will only heat what is directly in the way of its rays. There should be infrared radiators at least in front of you and behind you in an infrared sauna. If there are too few radiators, some parts of your body will not be visible to the rays and will not experience the heat properly.
Since the IR radiator is based only on the heat waves it sends out, it is usually ready to use as soon as you switch it on, whereas a traditional sauna takes 30 minutes or an hour to heat up. A smoke sauna will take several hours to heat up, but that's a different story altogether.
Few of the health benefits of high temperatures or sweating have been scientifically proven. The point of a real sauna is more in the relaxation and great feeling it gives. Only part of the feeling can be attributed to the heating process taking place in the body. While I can not promise a hot sauna or an IR radiator will have any health benefits, I am sure that taking a good, thorough sauna in good company will make you feel more relaxed.
There are many infrared heater manufacturers who will be happy to tell you more. One starting place is www.wasauna.com, a sponsor of the Finnish Sauna site. A Google search is a good next step.
Unconvinced?
Traditional saunas and infrared heaters don't really compete in the same category. The real sauna is more about the experience than merely bathing or health benefits. If you feel I am not doing justice to the infrared heater, you can voice your opinion by e-mail. I am particularly interested in hearing bathers' opinions on infrared heaters.