definitely boiling is no problem, but under the current times of ecological conscience, I think boiling for days is unnecessary, so much energy and not a big difference in yield/potency. Boiling makes the actives more soluble in the water, and breaks down plant matter to expose more of it to the water (also increasing the potency). But if one just takes care of breaking the plant material a bit further, before putting in the water, then a short boil (or even cold wash like dagger's technique) is enough