This is where it gets tricky. So many companies have said they have a 1 minute start up time. This does not mean it will generate full blast steam but may be referring to a smaller dual tank steam generator that produces a small amount of steam then shuts off after 10 seconds. This is cool when I want the steam to start immediately. Some steamers are instant that work similar to the hot water faucets that always have boiling water on tap that many people install in their sinks.
When I get home from a late night out, the first thing I want to do is go in my steam room. Well, if you have 2 generators it works double time especially with 2 steamers in each generator. For people that want a good steamer but want to sacrifice by waiting 15 minutes for it to heat up, these still give great steam. (note: many distributors trashed talked these lower end brands but when I used them they actually worked better than the more expensive fast start up brands but just took longer to start). I had to test all the different models to find out who was BSing me and who was just trying to sell their brand.
The latest models do not have the "always on" steam like the hot water dispensers in sinks. They have 2 boilers. The first one stays on for about 10 seconds while the larger tank builds up steam. They switch back and forth so it puts out constant steam. Most people prefer these to the ones that put out steam and you have to wait a few minutes for the steam to start back up again. I personally like a constant steam and don't like going from hot to warm for a few minutes and back to hot steam. If I want to freakin cool down I will take a quick shower or walk out for a minute. The latest steamers can put out steam within 1 minute with the double tanks. All this happens without people knowing since the steam comes out continuously. There is no clicking either.
Note: some steam generators work at full power until the temperature goes to a certain point and then the heater cuts back to 50% power to give a constant flow this way. These are the two types. Either having 2 tanks or a model that cuts back its power in half. This all depends on ones heat tolerance as the models that have this power variance are preferred by about 50% of the people and the other people want the dual tanks that can sometimes make the room so hot that it can cut the session time down.
Depending on how long you want your core body temperature to raise 3 degrees which is when most people want to get out of the steam room, this can help you decide which of these two types to buy. After knowing this, the 2nd thing I pick out is the wattage of the generator but not until the first decision is made. Many people just go by the wattage and buy a wattage that is too high for their steam room and get upset when the comfort is not like they expected and want to return the generator.
Take my steam room quiz and I will help you pick out the generator based on your answers.