Before knowing the liters per minute rating, always know if it is continuous or peak liters per minute.
Most people bring in about 12 to 20 breaths per minute. It is good to know how many average breaths you breath in per minute before setting the outflow liters per minute.
Most adults breathing in 4 to 6 liters per minute depending on their size at rest. when the person is exercising, the rate can can multiply 2, 3, or often up to 7 times as much depending on the exertion level.
When exercising, most oxy phobic people cannot process the oxygen as fast as they need and usually get tired and exhausted. they usually have sludge blood and cannot absorb the oxygen in the blood in the first place at normal concentrations without an oxygen concentrator. My goal is not to keep someone on a concentrator for life but to rid the sludge blood and make people more oxyphillic.
Warning: Don't just go by the maximum liters per minute but the concentration level of oxygen, which most people don't seem to realize till later on.
For those that are exercising they might need to use a oxygen concentrator daily and this is the only way people with low energy levels who fatigue quickly can actually work out.
The more the body becomes oxyphillic the less the concentrator will be needed and at lower concentrations. Working out with high oxygen conctrations can help people to work out longer and harder but tendon and muscles can be very sore the next day cuz the body got too much of an oxygen boost and the body normally would get fatigued in the right proportion to muscles getting fatigued. Kinda like using supplements that make you stronger when the body naturally can't o that far. The mind sees this oxygen and thinks the body is fine when actually its not. so the body works out harder and longer as the extra oxygen makes the cells produce more energy than normal.
Notice: I have to be careful when talking about excessive oxygen more than is utilized. Just like the humming bird example you don't want to burn yourself out. If the body is making more ATP than the body is normally naturally capable of handling.
When the cells normally are in anaerobic mode and you are trying to force it into aerobic metabolism, this is why most people I have talked to say to only use it just for a part of the time while exercising and training.
If the body is in anaerobic mode when it shouldn't and the cells are functioning in this way this is when someone can run into problems. It's like putting premium gas in the car when it say it is supposed to run only on regular. Or a better example, like going to the gym after work all tired and wearing those pendants made of hematite that raise the body voltage when really the body is givingthe signal that it it is tired and shouldn't lift any more weight or go another 20 minutes on the cardio equipment. It is not necessarily the having of too much oxygen that over oxidizes the body, it is the toxins and lactic acids produced because the body is working harder than it has the resources for.
Remember when trying to get a higher flow rate, with each extra liter per minute, the oxygen concentration sacrifices unless the concentrator is capable of producing more oxygen concentration at the higher flow rates.
If using the oxygen concentrator at rest or when doing light activities, doing errands, this is different than the concentration levels someone wants if doing exercises that causes heavy breathing and high exertion. It is much harder to get 95% oxygen concentration at 20 liters per minute than 10 liters per minute. Always know how many maximum breaths you will take per minute. Know if you will be using it while running on a tread mill or no more exertion than walking down the street. It is best to buy based on a few liters extra per minute than you think you need. You never know when when you will be using it, especially for those who become oxyphillic and sludge blood no longer is an issue as the body detoxifies.
On my oxygen concentrator quiz, let me know what type of activities you plan on doing and I will try to recommend the model that I think is right for you. Take my quiz here.