Hello,
I apologize if this question seems extremely elementary for the page but I am new to the flute/whistle scene and have some questions. Primarily, I am looking to find out what the main differences are between a low whistle and the standard Irish flute (besides end-blown vs. transverse). When in the same key the two instruments seem very similar to me and I was just trying to learn and be able to distinguish between the two. If I can play the whistle will I be able to seamlessly play the flute? Thank you.
No
To expand: The only area where there’s any interchangeability is in fingering patterns. Embouchure, breath control, attack, and flexibility in tone color (to say nothing of their different grips) make flute and low whistle significantly different beasts. From a player’s perspective, it’s a mistake to think of both as just tubes that you blow into to get hooty noises. And remember that this isn’t elitism talking; many accomplished fluteplayers are also accomplished whistle players, and they will say the same thing. Forming a good flute embouchure is probably the hardest thing to master, and for some it can take years. There’s more, but this should get you started.
And BTW, the more you listen, the more you’ll hear how the sound of a (good) low whistle and that of a well-played (good) trad flute really aren’t interchangeable. I mean, you can do it, but if the exact sound of a whistle is what you want, a flute will not do. And, of course, vice versa. 
Lots of differences, very significant differences. You posted this on a flute board, so I, like many others here, have a flute bias. But most whistlers would agree that:
–the flute can cut and project far more than a low whistle;
–strong flute tone takes years to develop the embouchure; low whistle, takes time and practice, but not to the same degree as flute;
–both take a lot of practice and it’s not easy to play both low whistle and flute well; for instance, I’m a decent flute player, but can’t play low whistle at all.
Perhaps worth noting that there are many performing and recording artists on Irish flute, relatively few on low whistle.
Oh yeah, right! 
So very few low whistle players out there. Nary a one. 
I’m relatively new to flute and whistle. I started with a Low whistle a few years ago and switched to flute. From my perspective there are a few differences - apart from what has already been said above about the effort required to develop the embouchure.
- In my experience, it takes a bit more breath to keep my flute resonating than my whistle did. That may just be because my embouchure is poor.
- I believe there is a bit more freedom of expression with flute. The fipple on the whistle is rigid. The embouchure used on a flute is very very flexible, and this allows you more control in your attack, volume, and tone.
Just my perspective.
If you are just starting out… why not try both and see what suits you?
I said relatively few ‘recording and performing artists’ on low whistle compared to the number of recording and performing artists playing Irish flute. That isn’t very few or nary a one ‘low whistle player,’ which also switches away from recording and performing artists to just people who play low whistle, of whom there are of course many.
Be that as it may, it’s not what the OP was asking about.
The OP writes: ‘Primarily, I am looking to find out what the main differences are between a low whistle and the standard Irish flute (besides end-blown vs. transverse). When in the same key the two instruments seem very similar to me and I was just trying to learn and be able to distinguish between the two.’ The fact I remarked may be worth noting perhaps reflects something about the expressiveness and flexibility of the flute. Sorry if this wasn’t clear.
In classic 19th century flute playing Nicholson and Rockstro give four completely different tonal color spectra available to the player. One of note, is the tonality of a trumpet or horn. Give a listen to Kevin Crawford in his ‘D’ Flute Album, and ask yourself if you have every heard a low whistle sound this way. A whistle maker can set his whistle up for one of the sonorities, for example the ‘cosmic drainpipe’ sound of what Nicholson calls ‘the hollow sound’, but having set the instrument up that way, then you are stuck with that one modality. Not so with a flute.
Bob
Jim, many pipers and flute players play low whistle as well as a good number of box players, fiddlers, etc.. The list of players, performing and recording on low whistle is long - if you pay attention to that type of thing. In the 90’s you couldn’t swing a cat without hitting a low whistle player. The density has only gone higher since.
But back to the OP. The advice given above about the differences between the instruments is good.
It is far easier to get a good tone out of the whistle - it is built into the design. The major drawback or hurdle with the low whistle is the finger span required to play the bigger low whistles. And the air requirements are greater (on average) with the whistle versus the flute. There are smaller holed low whistles and narrow windway models which can limit the difficulty a bit.
The flute is a difficult instrument on which to generate a good strong tone, as has been noted already. That’s the hard part. Hand span on a conical flute is, on average, less than on a whistle. The holes will usually be easier to cover on the flute. The flute is by far the more air efficient of the two instruments, once you get the hang of the embouchure thing. And the embouchure thing makes the flute the more expressive instrument as far as tonal colors and dynamics go. It is up to the skill of the player.
But whistles can be made with a dizzying variation in the head (and bore) design which will allow a variety of timbres to be generated, it is just more fixed, as has been said. So some of us tend to buy (or make) multiple low whistles based on their sound.
Many of us play both instruments. Which one you start out on is up to you. Each has their challenges and both have their rewards.
Feadoggie
‘Jim, many pipers and flute players play low whistle as well as a good number of box players, fiddlers, etc.. The list of players, performing and recording on low whistle is long - if you pay attention to that type of thing. In the 90’s you couldn’t swing a cat without hitting a low whistle player. The density has only gone higher since.’ Agreed. It is, of course, consistent with what I wrote. Thanks.
Jim, you said there are relatively few performing and recording artists on low whistle. Feadoggie said there are many (in the segment you quoted). That isn’t consistent with what you said 
. I do agree with you, though, that there are very many more (at least to my knowledge) flute players on music recordings/albums than there are low whistlers. However, this also ties into the OP’s question, in that another difference between the two instruments is that the flute is much more heavily rooted in Irish traditional music, whereas the low whistle is a more recent arrival, without the same long-standing track record of traditional usage that the flute has. Some people are even known to scoff at the low whistle in such contexts.
Everyone else has summed up quite nicely the primary differences between the two, though. You have a huge variety of control over tone, as well as the volume of each note, on a flute, whereas on a whistle it is much more fixed. On a low whistle you usually can’t really play specific notes louder or more quietly without pushing the tuning sharp or letting it go flat. Likewise, as mentioned, on a flute you can also produce a wide variety of tones. Listen to a good assortment of different skilled flute players, and you will likely hear that each player has quite a different sound, as well as takes advantage of producing a variety of different sounds in their playing. With a low whistle the tone stays much more constant. Both instruments can be quite expressive, but a flute gives more possibilities, in that regard. But, to take advantage of these various options takes a lot of time, dedication, and skill.
Low whistles overall have a different sound. Although flutes are capable of producing somewhat similar sounds to some low whistles, the low whistle still has it’s own sound which is unique to it, which some might like more than that of a flute. I especially notice the biggest difference between the two in the upper register. You also don’t have to spend all of that time learning the proper embouchure on a low whistle (though that’s not to say it doesn’t have it’s own challenges). Low whistle is an easier transition from regular whistle than the transition to flute is, at least in my experience.
Also, you are much more likely to find keys on a flute, which allow the playing of various semitones away from the notes that are played with the holes, as well as ones that can extend the range down to low C, or even lower. A few low whistles have been made with such keys, but it is rare.
I started with low whistle before later taking up flute. I play and enjoy both instruments immensely, but my preference leans greatly towards the flute. I mainly use low whistles for keys other than D, and this brings up another difference- You can often get a top quality low whistle in number of different keys for the same price that you can, in many cases, get a good flute for.
If you are wanting to branch out into one or the other, I think a low whistle is probably an easier transition for a regular whistle player. Doesn’t mean it is the better choice, but it’s at least easier to get a proper sound out of in a short period of time. I struggled for a long time just to get a decent enough sounding note out of a flute to be able to actually play it. I think for most people there is a pretty significant difference in the learning curve between the two instruments.
Let me add in addition my own 2 cents. I started playing flute about twelve years ago because I was playing low whistle on the street and needed more volume. Flute is a good deal louder, as folks in this thread have noted. Also whistle has its own windway, which is largely fixed. With flute you ARE the wind way, and that gives you a whole lot more control over the sound and ‘shape’ of each note. ROUGHLY it’s a bit like the difference between playing violin, or singing, on the one hand, and playing harp or piano, on the other. (When I play flute I sometimes try to imagine I’m singing.) So flute is, in this dimension anyhow, a good deal more expressive. I find flute very satisfying to play–partly for this reason. Of course they are also harder to learn to play, since you are the wind way and must develop the embouchure. Also, for this reason, I have a lot more control over the upper register of the flute. Also in my experience, anyhow, it’s easier to make the low end of flutes honk. Finally something personal, which is that I find the flute easier to hold (though it took me quite awhile to get the ‘grip’). I still play whistles a good deal, though they tend to be mid-range in key. As I think we all agree, plenty of people play low whistles, there are some extraordinary virtuosos, low whistles do some things and get some effects flutes don’t get, and we would be poorer without them. Best to all
I suppose the words “effort required” are okay, because finding an optimal embouchure is often a matter of dogged persistence wherein developing fluteplayers typically spend a lot of time, with their mouth muscles behaving as if they’re power-lifting, in the search for Right Embouchure. The irony is that when you do find it, it’s practically effortless, and you wonder why you went to all that face muscle effort for such a simple thing as positioning; after all, how does doing the wrong thing get you to the right thing? It doesn’t, at least directly. But I think the struggling is somehow still an inevitable and necessary part of the overall learning process, even though the light of a good embouchure will seem to bear no relationship to the darkness of what was going in in earlier efforts. I think it’s fair to regard the successful embouchure hunter’s efforts as a process of elimination, because while good embouchure can be very precise, it doesn’t require great effort, so if you’re lacking for a sense of direction, this one cannot fail you: If it ain’t pleasurably easy in all things, keep looking.
I would absolutely look to the embouchure for that, because so long as you have a good flute in good order, embouchure’s the only answer. Once you really start nailing it, you will be surprised at how little air it takes to play, and even play loudly. It’s all in the mouth/jaw/lips positioning, and in leaving pressure supply to the abdomen - IOW the right feeling isn’t one of blowing into the flute, but of breathing into it. Someone once said that playing a flute shouldn’t take much more air than what you expend while speaking normally, which sounds utterly counterintuitive, but wouldn’t you know it: the day came when I found it to be true.
Something to look forward to, isn’t it.
Along the same line, the old analogy of the garden hose that you pinch off to get a faster stream of water. Less water, more force. The good embouchure does that.
Another feature of a good flute embouchure is that it tends to improve whistle playing. If you hold the beak of the whistle in your lips, the good embouchure gives you SOME more control over the speed of the air entering the whistle (as in the garden hose analogy), thereby increasing your control over tone–though of course nothing compared to the control you have over a flute.
Yes, though of course you don’t need to play flute to learn that kind of embouchure control on the whistle. 
This is true. And, conversely, developing that embouchure control on the whistle can help prepare you for flute.
Really excellent advice and very true statement, Nano! I feel the same, and it’s why I could not give up the low whistle after I found the flute. And I really loved the flute, still do, but it’s not the sound you get from a low whistle. But truth be told, I play more low whistle now again, than I do flute because it’s the sound I like best. Edited to add: Low whistle was my first love in Irish music, and where my heart returns me by choice as a player.
Playing the whistle will give you a good basis in the music and notes, so you may later move to the flute with an advantage, but if you really want the flute sound, then maybe you should start there. Undivided attention is always best in such pursuits-concentrate on one at a time, and you will go further, faster.
Follow your heart on this one, and you will have a good start. More good advice has been written, I see now too, reading back on the post.