I try to run one nipple for every 4-6 birds but have stretched it to 8 birds in a pinch while waiting for nipple and was ok. I just think it's better to have more than needed if you can in case one fails. I have heard of ice collecting on the outside of the nipple but haven't had that problem myself but in w Kentucky it rarely gets below zero, maybe twice in the 15 years I've lived here. It could be a different story up north. I just think since heat rises it's better to have your heat source below the nipples.