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Discussion in 'Coop & Run - Design, Construction, & Maintenance' started by worms7, Nov 5, 2016.
If I am going to put vents on my
Shed for air flow should i put them high up
In England you shouldn’t have winters that cold compared to many, I spent a year there several decades back and the weather for the most part was much nicer than your reputation. It can be damp though.
What you want in the winter is some air movement to exchange good air for bad but without strong breezes hitting your chickens while they are on the roosts. There are different ways to achieve that but to me the easiest is to have lots of openings up high. That way you get air movement across the top of the coop which will create turbulence so you get air exchange, but any strong breezes just pass overhead.
Do you need ventilation near the
floor as well as at the top
No, you do not have to have vents near the floor in winter. In some designs openings down low are OK, in some designs they are not. What you want to avoid is creating a wind tunnel where breezes hit the chickens. If your coop is big enough you can have openings low on one end with openings high on the same end and have the roosts on the far end so any air flow is up and not directed at the roosts. The “Woods” coop design is a good example. Those are used in Canada where it gets a lot colder than you will see in England. You create a cul de sac out of the wind path. The wind through the two openings up front create enough turbulence to have good air exchange without creating strong breezes where the roosts are. If you incorporate a droppings board in your design that can block any breezes coming up from below.
If you have openings above the chickens’ heads when they are on the roosts, you create an area of relative calm under the breeze that passes over their head. To me that is the easiest way. Those overhead breezes will still generate some turbulence in the coop to stir up the air but it’s gentle air movement. But there are different designs where you can have openings down low.
In summer openings down low are a good thing. Even in England heat can be your enemy, though again you won’t get as hot as many places. Being on an island with the Gulf Stream moderates your temperatures quite a bit, winter and summer. But in summer breezes hitting the chickens is a good thing, not a bad.
All this is about when the wind is blowing. Sometimes the wind does not blow, it’s dead calm outside. When it is dead calm no breezes will be blowing. You still need to exchange bad air for good. That’s where openings up high come in really handy. Warm air rises and warm air holds more moisture than cooler air. Ammonia gas is produced by damp poop decomposing. Ammonia gas is lighter than air so it also rises. Openings up high allows ammonia and warmer moister air to rise and escape.
This only works when there is a difference in air temperature with the warmer air inside. The heat to warm that air can come from the chickens themselves, their warm poop, the sun hitting a wall and warming the coop (Yes, even in England. The sun does sometimes shine), you might have a heated waterer giving off heat, or if your coop is on the ground the soil will probably be warmer than the air temperature, especially during cold snaps when you are most concerned. If the air inside is warmer than outside and you have openings up high gravity will provide the force to move that air.
One trick to help generate this difference in air temperature is to have an opening down low where the air is cooler than the air inside to make it easier for cooler air to enter, especially in the summer when it is dead calm outside. If you put this opening on the sunny side where the air heats up you won’t get as much benefit as if you put it where the air is always in the shade and cooler. It’d the difference in air temperature that provides the energy to move air so the more difference in temperature you can generate the better.
Even in winter if you can have an opening down low where the air is cooler than the air inside you can generate pretty good air movement. But if the air temperature is not cooler down low as compared to your openings up high, it will not make any difference to gravity where the cooler air comes from. Remember you do not want to create any breezes where the chickens are roosting when the wind is blowing. Openings down low in winter are fine as long as you avoid breezes.
I'll digress only to say that some ventilation down low IS important with some designs. The issue is CO2 gas, which the birds exhale. CO2 is heavier than air, so it sinks and must be allowed a pathway out. If that is allowed to accumulate along the floor with no way to drain out, that is not good. That is the foul (fowl?) air the old timers used to talk about in chicken houses. It was a constant theme mentioned in the old books on chicken house designs.
So with each breath, birds exhale water vapor (their lungs are their only radiator) and CO2 gas. The exhaled water vapor is warm, so tends to rise, and the CO2 sinks. That is the challenge of ventilation. Getting rid of those two gases (plus ammonia off the droppings), high and low, without making the coop drafty to the point wind chill kicks in. A neat trick if you can do it.
That is why I am such an advocate for the Woods open air coops. They have one end that is entirely open (high and low), yet are not drafty. They do this since they are essentially a rectangle, with one short side being open and the roosts on the opposite end in what becomes a dead air space.
If you wanted to use another design, stick with the rectangle plan. Make the long side of your rectangle at least 1.5x the short legs and 2x would be better. Then place the short leg open side (it can be wide open) so it faces south to the winter sun (north to those down under, but they already know to reverse this kind of stuff). Put the roosts at the back and if it is a small coop, you can add other tricks like putting your nest boxes beneath the roosts, with droppings board between them.
Coop designs with the wide side open (like the old Quisenberry Fool Proof House) had to go to elaborate measures to get the same level of ventilation, without drafts. They had ventilation down low, but used baffled vent boxes, etc. to do it.
A lot depends on how airtight the coop is down low or up high for CO2 or ammonia. Since they have different weights than air, it doesn’t take a lot of cracks or open space to get rid of them, gravity is really efficient. For most of our small backyard flocks the numbers of birds help keep the risk down and most of us don’t build airtight designs. I sure don’t. Moisture in freezing weather is usually our highest risk.
I’m not arguing with Howard at all, he has a good point. Some designs will need a small opening down low. It’s challenging to be general on here because there are always exceptions.