How do you balance ventilation and warmth in a poultry house?

I am trying to understand how people balance fresh air with temperature control in poultry housing.
Too little ventilation can create moisture and ammonia issues, while too much uncontrolled airflow can make birds uncomfortable in cold or wet weather.
What design details have made the biggest difference for your setup: ridge vents, side curtains, fans, insulation, house orientation, or stocking density?

I'd suggest reading Fresh-Air Poultry Houses: The Classic Guide to Open-Front Chicken Coops for Healthier Poultry by Prince T. Woods: https://www.amazon.com/dp/097217706X (And I think the text is available online for free if that's easier for you.)

And check out this thread: https://permies.com/t/177926/shelters-habitat/Woods-Fresh-Air-coop-build

Emma I'm afraid you get the typical permaculture answer. It depends.
I live in N. California, and have a very open coop. In the winter I put a couple of corrugated steel panels up so my hens are not getting wet on the roosting bars if it rains. It's  kinda closed in on 3 sides in the back of the coop, and the rest is pretty much chicken wire. For me I have to worry more about the heat than the cold.
How cold will it get where you live?  
I hope someone else chimes in, we think we are freezing to death if it gets into the 30s, so I'm probably not the best source. Good luck.

My experience from farming both on and off grid is that chickens are tough. They're tougher if they're heritage breeds. Chickens can be cold, wet and in drafty conditions; but only one of those at a time. I prioritize ventilation over heat and make sure their house is dry with a place to get out of the wind.

Back when all I had was a 15x30 tent, the floor was steaming in -20 degree outdoor temperatures, with the potential for frostbite from moist air being the biggest problem, thus the priority was on ventilation.

Chickens are pretty sturdy birds. I had a coop which was nothing More than a 8'w x 6'h x 3'd plywood shipping box with doors cut into it, back on the property I used to call my redneck proving grounds where I learned how to put permaculture into practical action, and my winters dropped to -5 or so on several nights each year I had the chickens.

They were fine.

But, if you're getting really cold, a thermal flue connected to an insulated underground pipe run (like Amish AC, but you could run it in u-shapes rather than a big long run, since maximum efficiency isn't your goal), it would help keep the coop cool during the day, and would provide adequate ventilation during the night while still allowing you to insulate the coop against the cold.

You can even hook up a little fan if you like.

I drew a shitty little diagram to give you a better idea of what I mean.

My experience in USDA zone 4b/5a is that the ventilation issues are much more deadly than the cold issues. Chickens are birds which handle cold temps differently than humans. I have never had a chicken die from cold... I have had a chicken get frost bite from lack of ventilation. I have also had a chicken die in a way that seems to point to lack of ventilation. In my climate ventilation comes first... then I deal with the temps if needed.

Warmth is alwais a mix of radiation and air temperature. If a part of air must used for ventilation, than rais up the amounth of radiation. This can be don by hotter the temperature of the heater, or and better, by instaling more heater surface.
Warm greetings, Fetze Tigchelaar Netherlands.

Strongly agree that ventilation is the most important thing for chickens. We had chickens in the Interior of Alaska (the coldest part of the state, and one of the coldest inhabited parts of North America), in a somewhat drafty little barn (shared with a couple of goats and a few rabbit cages), and while we did lose a few combs and even a toe or two, the birds survived and continued laying. If I was back there again (I'm too old to like seven months of snow-on-the-ground!), I'd probably build a tighter small barn, and give the chickens not only more bedding, but no roosts in the winter, so they'd have to sleep with their feet on the bedding pack, which self-heats. But I would also put some kind of heat-exchanger ventilation system in it. We didn't have that option back then, as we didn't have electricity where we were living.

Later on, we lived in central NH for a number of years, and had some chickens who decided that their roosting place was either in the trees across the road, or in the branches of the big ancient amur honeysuckle bush next to the house. Even through thirty degrees below zero, with snow, or rain in the summer. I don't remember ever losing a hen to the winter, although the owls picked off a few of them.

If you have really cold winters, select chickens suited to the climate - large-bodied and small-combed. I don't like feathered feet, myself. Some people recommend them for cold climates, but in my experience with some Light Brahmas, the foot feathering just collected ice balls or mud balls, depending on what time of year it was. And they lost just as many toes as the hens who didn't have feathered feet.

If you don't live in a climate that gets really cold winters, then the only factor you need to worry about is ventilation. Keep them dry and out of the wind as much as possible, but the three-sided sheds, with one side wire, talked about in the book mentioned above (which were used in, IIRC, Vermont or upstate NY), are completely adequate. If you are where it gets really cold in the winter (way below zero, F), you can build the three-sided shed, but have shutters to close at night in really cold weather. Just make sure to open them first thing in the morning.

Also, use deep bedding. Someone I used to know who had a farm in upstate NY would completely fill her hen-house with leaves every fall. Filled to the ceiling! Then throw the hens in and let them pack it down. Clean it out in the spring, and there is some of the best stuff for the garden that you ever saw. (Have a few bags of leaves stored to add if they need clean bedding, but don't clean it out until spring.)

Another very helpful thing is to have a heated waterer, so they always have water to drink. They can get by with snow, if they have access to the outdoors, but they'll do better with water. (Again, we didn't have that option when we were at the off-grid place in Alaska - I would take hot water out to all of the animals twice a day. You really don't want to have very many animals if you have to do that.)  

Emma Grace Wilson wrote:I am trying to understand how people balance fresh air with temperature control in poultry housing.
Too little ventilation can create moisture and ammonia issues, while too much uncontrolled airflow can make birds uncomfortable in cold or wet weather.
What design details have made the biggest difference for your setup: ridge vents, side curtains, fans, insulation, house orientation, or stocking density?

You don't tell us where you live, Emma Grace, but since you were writing in August you are likely more concerned with excessive heat. While ammonia can be a very serious issue, let's assume that your chickens are kept reasonably clean. These descendants of jungle fowl are actually more sensitive to the heat than to the cold. Try to maximize the time they spend outside by offering abundant shade there. (The more time they spend outside, the cleaner the coop stays, too. Yeah!). If you could shade the whole coop, that would be great too. One thing I've done during oppressive heat is put a bag of ice cubes (like 10 Lbs) in their water. I've got the rubber bowls. That was just about the best thing to cool them fast. Have some water outside too. Several bowls. I'm amazed at how much they drink
Stock density can be an issue: shoot for 3-10 square ft per bird, depending on the number of perches.
I would not bother with curtains that will diminish light and get dusty/dirty.
Insulation? of course, absolutely.  The frost can go 48" into the ground  around here, so that's not optional, and it's cheap for long term comfort. It also slows down great variations in temperature. . When it gets really coooold, I have a ceramic heater hanging from a wall)
Fans cause drafts, so they are not very good either.
Ridge vents are very useful, insuring an exchange of air without causing a draft and they work all the time with no energy input.. How may windows do you have and can you open them? : In multiplying windows, you multiply free light and  the possibilities of airing the coop. I added 4 and I now wish I had made them larger. Install once, use forever. Just make sure that you put some serious wire, like 1/2" or 1" to stop all predators.
My biggest surprise, raising chickens was to realize just how much cold they can endure. I used to think "jungle fowl, they must like it tropical". Well, nope.
Even in -30F, I leave the trap door open during the day, and they all do go out, (unless there's too much snow, of course). I built a secondary "coop", attached to the first that's just a hoop house, (reinforced with tight wire, of course). It comes in real handy when I want to clean the main coop. It can get extremely cold in there, but it's very dry, and they even have a big, huge dust bowl in there, for when the weather is inclement.
So good luck if you need to make renovations.

Frostbitten chickens are not the happiest chickens. Ventilation is incredibly important in a chicken coop, but what can be even more important is where it is located. Having a draft where it won't blow across a chicken's body is ideal. If a draft crosses over a chicken's exposed body (comb/waddle) it can damage the flesh. The way I answered this in my henhouse is by having my ventilation up high at the roof line. I have very little exposed but it seems to do enough.

I use a coop that is mesh on the front back and bottom.
It sits under a  large transparent pergola, acting as a second roof, with many feet of distance between the two.

In the winter, I use blankets to close in the sides and deep bedding to insulate the floor.
They will often "roost" in the bedding, but even when they don't
My chickens occasionally spend 4-5 days inside in the winter, due to cold or snow, and they have never shown any signs of respiratory distress even then.

Side note, when the snow is deep and you don't want to shovel,  you can throw down a bag of autumn leaves on top of the snow.
This will often, but not always, be enough for my birds to come out despite the snow.
I do push them outside after a few days of them lingering inside, to air out the coop, and off course I bring food and water to them in these situations.

Honestly, a  big enough hoophouse filled with bedding  could be home year round, no fuss at all.
In the summer, add shade cloth and vent both ends.

Emma Grace Wilson wrote:......
Too little ventilation can create moisture and ammonia issues, while too much uncontrolled airflow can make birds uncomfortable in cold or wet weather.
.....

Can you provide some sort of idea of the climate you are in that you are trying to build for?   The buildings our chickens are in have full windows open in the summer (days 80s to 100 degrees F), but few chickens are in there during the day as they are free-ranging on the property.  By night, it has cooled off to ~60s or 70s F so they are fine with that.  In winter with cold nights between -30 to 0 degrees F, heat lamps help to keep them warm and by day, if sunny, the greenhouse design factor takes over and the buildings can reach between 20 to 40 degrees F, occasionally assisted by wood stove.  At 20F and above on sunny days, they will be out pecking around in the driveway.

Ventilation is my priority too.  I had a chicken house tall enough for me to stand up in.  I put the roost bars at least 5 feet off the ground.  The roost bars must be wood, not metal.  And a tree branch is better than a dowel because they can hold on better, and the diameter of the branch isn’t uniform.  Better for their bones and toes.  There were a few air leaks around the door and windows, and a small chicken door down next to the floor.  

Chickens can keep their feet warm by crouching or kneeling down, or what ever you call it.  Essentially, they cover their feet and legs with their feathers.  They also can roost closer or further away from each other.  

Chickens are hardier than some other birds.  They can roost in the trees, they make a chirring sound when roosting, I think that’s how they find each other and keep each other close.  Compare that to guinea fowl.  On the same night the chickens roost in the trees, the guineas freeze and fall to the ground in feather covered guinea shaped ice.

Protect the chickens from wind and drafts.

Also, I did once build a cob greenhouse adjacent to the chicken house, with an adjoining window.  That was a nice setup!