In the world of oxygen concentrators, and with most other machines and appliances, smaller is always preferred. However, smaller also generally means a lower oxygen capacity. If you can find a small oxygen concentrator that can deliver the oxygen dosage that you need, you're in luck.
Small, medium, or large, the one you choose should fit your lifestyle and meet your oxygen needs.
Small Oxygen Concentrators
The smallest of the portable oxygen concentrators are categorized here if they weigh 5 lbs or less, with or without an external battery installed. A few of the smallest portable models are...
The AirSep Focus at just 1.75 lbs. The unit stands at 6.4 inches tall and 4.8 inches wide, and has a maximum pulse dose oxygen capacity of 330 ml/min. It comes with 2 batteries, which weigh .53 lbs each. Even with two batteries, the Focus only weighs a total of 2.81 lbs!
It's cousin; the AirSep Freestyle only weighs 4.4 pounds by itself, and a few more with the supplemental battery added on. This small portable concentrator can deliver up to 498 ml/min.
The Activox weighs just 4.3 lbs and the Activox Pro weighs 4.8 lbs, and can deliver up to 3 LPMeq and 4 LPMeq, respectively. These two also have amazing long-lasting batteries.
The smallest stationary oxygen concentrator on the market is the Respironics SimplyFlo, which only weighs 9 lbs. Most stationary oxygen concentrators are bigger than this because they have a much higher oxygen capacity. If you only need up to 3000 ml/min of continuous flow oxygen, the SimplyFlo is perfect.
About 30 lbs and under is considered on the small side for stationary concentrators, which usually aren't taken outside the home. The Respironics EverFlo has settings from 0.5 to 5 LPM (0.5 increments) continuous flow, and it weighs just 31 lbs. It rolls on wheels, so it's easy to move from one room to another.
Medium Oxygen Concentrators
Medium portable oxygen concentrators can offer higher oxygen capacities and longer-lasting batteries than the smaller ones. These would be like the Respironics SimplyGo and the Inogen One G2. Medium portable oxygen concentrators are between 6 and 10 lbs by themselves, or with the external battery installed.
Medium stationary concentrators offer an even higher continuous flow oxygen dosage and weigh between 30 and 45 lbs. This would be like AirSep Companion 5 and the Invacare Perfecto 2.
Large Oxygen Concentrators
The larger portable models, as well as the medium ones, and usually carried around with a mobile cart instead of a carry bag. The Sequal Eclipes, Sequal Equinox and the Devilbiss iGo fall into the larger portable category, and weigh more than 10 lbs and less than 20.
The large stationary oxygen concentrators weigh more than 45 lbs and can deliver as much as 10 LPM of continuous flow. Some of them also have other features, such as doubling as a nebulizer machine.