Here is the answer: How often? Actually it depends on you. When you need to. When they quit working, begin to taste bad, or stop working as well as you want, replace them. (If they never worked as well as you desire, then they were wrong for you in the first place; replacing them won’t help.) Atomizers quit working for a number of different reasons: The coil burns out or becomes internally disconnected in some other way. In this case, you must replace (or rebuild, if this is possible with your particular atomizer). This is random, although high-quality, authentic atomizers tend to last longer than cheap clones.The wick material gets clogged up. Many flavorings will clog the wick directly. This can happen in a few days with some dark flavorings. Many others will clog the wick if the coil gets too hot, either from letting the wick get slightly or nearly dry. (Keep your tank with at least some liquid in it; never vape it dry.)If I am careful to not let my tanks run dry, I can easily get six months or a year from my atomizers. It can also happen if the wattage is set higher than the coil can dissipate, or boils off juice faster than the wick can deliver it. (EDIT: And as Alvaro says: prime wicks before using; dry is the enemy of atomizers.) The wick material gets charred. This only happens with cotton/rayon wicks. Wicks which are made of heat-resistant materials won’t char (but they will clog as in #2). Again, this happens when the wick gets too dry or the wattage is set way too high.Sometimes you can clear the clogging (but not charring) by various kinds of rinsing or washing, but I haven’t had much luck with this. If the coil is still good, you can rewick some atomizers; if it’s possible, there will generally be some YouTube videos showing how to rebuild or rewick a particular atomizer. Watch several, since they may be using different techniques, and you may find one easier than another.I, personally, vape completely unflavored, high-nicotine e-juice* at very low wattages. I only vape for the nicotine. I don’t get giant clouds (and don’t want them; I stealth vape most of the time). What I do get is extremely long atomizer life.