Well, perhaps they have improved over the years. 20 or more years ago, I used to maintain a system that had about 40,000 of them. And I found and replaced leakers every single day.
Thinking about dripping nipples, and knowing I may have to move the water inside during the winter, I decided against the nipples and went instead with these: http://cgi.ebay.com/ws/eBayISAPI.dll?ViewItem&item=281130738417&ssPageName=ADME:L:OC:US:3160
They can be mounted on the side of a...
Nope, my birds are... not even here yet!! LOL, they arrive tmrw. I only mentioned that because I don't know where everyone is. In the South USA, I don't imagine extra heat will EVER be needed. Chickens produce a fair amount of body heat. But the more space you have, the less heat per cubic...
Some will recommend 2 sq ft per bird if they can range, so doubling that (as you have) should be great. If they spend more time outdoors, and only roost inside, then you are good for warm weather (just don't forget vent holes; I put wire-covered holes down low that can be plugged when it turns...
Maybe a pic will help. You can scale this up as needed. I went with 4' high in front, 6' wide, and 4' deep, planning to keep about 8-10 birds in it.
http://poultry.purinamills.com/stellent/groups/public/documents/web_content/ecmp2-0160674.pdf
Some may disagree with me, but if you let your chickens out to range most of the day, then you only need about 2 sq ft per bird of roosting space. You have about 64 sq ft now, so you can house 32 birds comfortably. But if you want more space, feel free to build a second coop. Unless you just...