hi guys, i am part of the uilleann pipe forum & i have just ordered an overtoun low D whistle, just how much breath are we talking here as my lungs are getting on a bit, is it huge effort or just controlled consistencey in the breathing ??? 
At the low end, very little breath. Not so much a blow as a breath. At the very high end it’s still not a lot. Unless you’ve got a disease it’s easy. Control is the issue, but compared to controlling the bag, it’s easy. We breathe all day, squeezing bags…no.
Depends on the whistle.
My Burke LDPV requires a lot of lungs above E in the second octave, and has a lot of volume and brassy wind noise (part of its charm).
My Reyburn (don’t tongue the low D) requires far less lungs in the second octave with lower volume and a rich voice (part of its charm).
I can only compare the two because that’s all I have.