There has been a bit of a discussion in our party. One player is playing a Dragonfire Adept. His class has given him quite a variety of breath weapons, and only one of them has an actual cooldown (and thus behaves like a normal Dragon breath attack.) He has taken a metabreath feat that has the pre-requisite of having a breath attack with a cooldown. Now that he has taken the feat, can he also apply it to breath weapons without a cooldown? I am currently not aware what the feat in question is, but will add that info when I find out.
RAW: yes, he can use it
The rules for metabreath feats in Draconomicon (and the one from Dragons of Faerûn) state that they require a “breath weapon with a cooldown,” which the dragonfire adept’s breath weapon arguably lacks (some do make the argument that it has a 1-round cooldown, but Dragon Magic itself never describe it in those terms).
However, these same rules state that this is a requirement for taking and using the feat, but do not state that the effect of the feat applies only to such breath weapons. These feats add some number of rounds to the cooldown, but the wording they used to do so is, e.g. from Lingering Breath,
When you use this feat, add +2 to the number of rounds you must wait before using your breath weapon again.
Note how it doesn’t even reference any “cooldown,” it just adds some time before you can use your breath weapon. This effectively gives it a cooldown if it didn’t have one.
Thus, RAW, a dragonfire adept arguably needs to get some second breath weapon that has a cooldown to take and use these feats, but once he’s got one and has taken a metabreath feat, he can apply it to any breath weapon he has, including the dragonfire adept one, not just to the one he used to meet the requirement.
In practice, this may be a case of “the rules don’t say I can’t,” but...
It’s not uncommon for feats in 3.5 to have requirements that are more narrow than their effects, such as this case where you need a particular sort of breath weapon but the effect does not repeat that limitation and applies to just “breath weapons.” It is pretty common to use RAW here, and accept that as how things work, but it is also a situation that may not sit well with some DMs.
However, at least in this case, the restriction of metabreath feats to only those breath weapons that have cooldowns seems unnecessary. It seems to exist to make them more “dragon-y,” but the dragonfire adept is plenty dragon-y (at least as much as the dragon shaman, whose breath weapon definitely does qualify). It may also have been added thinking that it would be necessary to make the cooldown extensions work correctly, but as we’ve seen, the wording ended up such that they work just fine even if the breath weapon previously did not have a cooldown.
As such, I recommend allowing dragonfire adepts to use metabreath feats, and without making them jump through the hoop of getting some breath weapon with a cooldown. They aren’t very powerful.
Also, side note: Races of the Dragon has “Breath” feats rather than “Metabreath” feats. These do not require a cooldown to begin with, and work just fine for a dragonfire adept, RAW and without hoop-jumping.
Draconomicon states that you need to have a breath weapon "whose time between breath is expressed in rounds. Therefore a hellhound (which can breathe once every 2d4 rounds) can take MB. feats, whereas a behir (breath weapon usable 1/minute) cannot." (Drac. p. 66) So all other types of time expression are explicitly ruled out (1/day etc.).
So if there is no explicit mention of rounds between uses of his breath weapon, he cannot take a metabreath feat by RAW. If he has at least one type of breath weapon with a "time between uses" given in rounds, he can take metabreath feats and apply the feat to all breath weapons he has, no matter the "cooldown".
As player breath weapons tend to not break the power bank, I see no reason to not let him use it that way.
Edit to address comments:
I think the important point is that the "cooldown" has to explicitly be given in a number of rounds. Thus the behir is excluded. From the rules it is impossible to "convert" minutes to rounds in this context, as the behir passage shows. If the DFA only has e.g.: "As a standard action, use this breath weapon", then RAW it would not be eligible to metabreath feats. Does this make sense? No. But this is the RAW.