What does "47 ppm at 2 l/min (500 mg/h)" mean on an ozone sauna spec sheet?

This is the specification buyers most often use to compare one ozone sauna against another, and it is the one worth understanding properly.

The three quantities are not interchangeable

• Ozone output (mg/h) is the mass of ozone the generator produces per hour. It is a quantity. Our Standard, Deluxe and Red Light saunas all use a 500 mg/h generator.
• Flow rate (l/min) is how fast oxygen passes through the generator. Ours is a constant 2 l/min.
• Ozone concentration (ppm) is how much ozone is present in a given volume of gas, as a ratio. A concentration only means something once you know which volume it refers to.

What the 47 ppm actually describes

It is the ambient concentration inside the sauna as a whole — the entire air volume you are sitting in — with a 500 mg/h generator running on a 2 l/min oxygen feed. It is not the concentration in the delivery line, which is much higher in a much smaller volume, and it is not a room-air figure. That is why the number reads as modest next to the generator’s output: the ozone is being distributed through a large enclosed space, and part of it reverts to oxygen or reacts with moisture as the session runs.

The figure also fluctuates a little in practice, because it depends on how much of the sauna’s volume the person inside occupies. Body size, build and weight all shift it slightly.

The 10 levels

The digital display gives 10 ozone levels. Each step raises the generator’s output by 10%, so level 10 is the full 500 mg/h and level 1 is a tenth of it. The oxygen flow does not change with the level; it stays at 2 l/min throughout.

What to ask any manufacturer

Ask for the output in mg/h, the oxygen flow rate, and — for any ppm figure — the volume it was measured in. Without that third piece, two ppm numbers from two manufacturers are not comparable.