I don’t like the word “draft” in this context. When people think about a draft they think of taking a candle around their windows to see if there is any air movement even if it is so light you can’t feel it. That’s not what we are talking about with chickens. You need some gentle air movement to replace bad air with good.
Just like wild birds that overwinter, chickens keep themselves warm by trapping tiny pockets of air in their feathers and down. These tiny pockets of air are great insulators. If they get hit with a strong enough breeze to ruffle their feathers these air pockets can escape and they lose their insulation. The “draft” you need to avoid is a breeze strong enough to ruffle their feathers.
Ventilation is good air coming in to move out bad air. You have to have some air movement to accomplish this, but not much. There are different ways to achieve this. Many use the concept that warmer air rises and cooler air sinks. It doesn’t matter if you are talking about cold air in winter or the hot air in summer, you are talking about differences in the air temperature. If you have an opening down low on the shady side of your coop where the air is cooler than on the sunny side, the cool air will flow into the coop and push the hot air out of openings up higher. That works pretty well in the summer, provided you have enough openings. In warmer weather it doesn’t matter if a direct breeze hits them anyway, they’ll enjoy that. I keep a window at roost level open, that’s a prime roosting spot for the dominant birds.
In the winter you can get heat from the birds’ bodies and breath, from their poop, from heated water dishes if you use those, or if your coop is on the ground, from the ground during the colder weather. In cold weather this is enough movement to exchange the air, again provided you have enough openings up high. You don’t need openings down low, the cooler outside air will come in those higher openings. Remember you are talking about differences in air temperature, not absolute hot or cold.
In winter, if you have openings up over their heads when they are on the roost, any breeze will pass right over their heads when you have a wind blowing. This cross breeze will generate some turbulence in the air down below to help exchange good air for bad, but won’t hit them with a strong breeze. Even without a breeze, you will still get an exchange of air just from the warmer air rising. This is when you don’t want openings lower down that can create a breeze that hits the chickens. There are some specialty designs that have openings fairly low in winter, these work well even up in Canada. The chickens roost in a quiet spot in the back where breezes don’t hit them while the air is exchanged up front. There are always different ways to accomplish any of this.
In your climate you probably never need to worry about cold at all. It just doesn’t get that cold. I’d think you could have a lot of ventilation year around high and low. But in the winter it won’t hurt to block off some of the lower ventilation to cut down on the breezes hitting them directly if you wish. In your climate your summer heat is your enemy, not your winter cold. And that close to the water you are in much better shape than people further inland. You are right, bodies of water moderate extreme temperatures. When I lives in Louisiana there was normally a 5 degree difference on the north shore versus south shore of Lake Pontchartrain.
So open your coop up and let some breezes hit them now. Don’t worry about it being too cold for them. At seven weeks they could handle temperatures below freezing without problems if they are out of a breeze. At that age and in your temperatures a breeze will feel good. Let people further north than you worry about cold. You don’t have to.
