There are about 5 different types of heating elements to heat up an infrared sauna. They are carbon panels, ceramic rods, red infrared lamps combined with Jade rocks. The most common are the carbon panels and the rod heater saunas are still popular but becoming less popular. The most expensive but very popular is the carbon rod combo heaters. There are now, as of 2013, dual back to back carbon heaters that was developed to heat up the sauna quicker, 10 minutes instead of the average 15 minutes to 20 minutes. It was found that utting two heaters back to back eliminated EMF to make the EMF emmissions negligible.
The carbon heaters are good because they keep a lower surface temperature that creates longer more penetrating infrared rays.. BUTTTT, they don't get hot enough for people that want a really hot sauna. The rod saunas definitely make me sweat more. The combo rod/carbon heaters even make me sweat even more.
Note: there are several different companies making combo rod/carbon heaters. There are some really low fluence carbon heaters that don't get as hot as the premium carbon heaters and some have rods in there so the sauna can get hotter because it can't get up to 140 degrees without the rods. I just don't want people thinking they are getting a rod/carbon combo heater thinking it is better when only the rod heater is there because the carbon sheet is not quality. A quality carbon panel gets much hotter than the cheap type.
Note: With any carbon heater, the infrared rays will usually be dissipated after 3 feet. Many people feel more of the fluence from the heaters in the smallest sauna for this reason.
The carbon heaters will always have a longer more penetrating infrared wavelength but will not get as hot as a rod heater. For the people that really want a hotter sauna, having a rod or rod combo is usually preferred.
The ceramic heaters can produce more of the optimal wavelength but don't penetrate as deep as the carbon.
It does however produce more infrared heat but doesn't penetrate as deep.
The more heaters the sauna has the better. Some have fewer heaters but have to be turned up higher (140 degrees) to get the far infrared while a sauna with more heaters can be turned down in temperature and get the far infrared that way while keeping the sauna closer to 110 degrees. The 2 person sauna is the most popular because of the price. Most have about 6 heaters. Some of the more expensive ones have 9 heaters. Those 3 extra heaters makes a big difference in the fluence I feel. Depending on how its bought, it is possible to get one for around 1000 dollars or slightly more depending on the options. The dual carbon back to back heater sauna will always cost more as the doubling up on the heaters jacks up the cost.
Note: The lower the temperature of the surface of the carbon panels, the longer the wavelength to penetrate deeper.
As you go up in temperature the broader the fir spectrum is. Better designed heaters can maintain the broadest range of the far infrared micron range much longer as the temperature goes up. Many saunas might just be at the higher spectrums near 14 microns and still claim they are an infrared sauna which is still cool but may not be what some people want. As the heaters age, the micron range on higher end heaters don't change that much.
Most lower quality carbon sauna heaters give off about 90% of the heat in the 8 to 10 micron range and over time produce even less of this range as it ages. I prefer a sauna that has a range from 7 to 14 microns which is the broadest range you can get. 8 to 10 which is more common on some of the models is cool with me but as long as I can get my hands on the broader ones, I feel like I am missing out on the broader ranges. 8 to 10 microns still works but its just not the fullest range I can get. While I am sitting in the sauna, it is nice to know if I am getting the broadest range.