Chicken Coop Ventilation in Winter: Moisture Out, No Draft on the Roost

Why a winter coop needs open vents

The instinct in cold weather is to close everything. The extension services advise against it, for a reason that starts with water.

According to the University of Wisconsin–Madison Extension, chickens drink about two pounds of water for every pound of feed and excrete a great deal of it in moist droppings. Dr. Jacquie Jacob of the University of Kentucky lists the sources of moisture in a coop: the birds' breathing, their droppings and spilled drinking water. In a closed coop all of it stays inside.

Three problems follow, each named in the sources:

• Ammonia. Wet litter produces ammonia. Wisconsin notes that even fairly low levels irritate chickens and their keeper.
• Respiratory disease. Damp conditions raise the incidence of respiratory diseases (Wisconsin). Ohio State University Extension names ammonia buildup in a tightly sealed coop as a cause.
• Frostbite. Ohio State states that humidity in a poorly ventilated coop predisposes chickens to frostbite, because humid air creates more frostbite risk than drier air. The details are on the page about frostbite in chickens.

There is also the matter of feel. The University of Maryland Extension points out that damp air feels much colder than dry air and makes it harder for the birds to stay warm. Penn State Extension sums it up: poultry handle cold very well if they are dry, while cool and humid conditions create health problems.

A heater does not solve any of this. It warms birds or air; it does not remove water. That is why every extension service read for this site puts a dry, draft-free, ventilated coop before any heat source.

Ventilation and draft are not the same

Both are moving air. The difference is where the air moves.

The University of Maryland Extension describes the goal: fresh air entering the building should mix with the warmer air inside before it gets to the birds. Holes that let wind blow directly on the birds can chill them. Maryland suggests filling such holes with spray foam or hanging a thick plastic sheet or tarp over problem areas. Ohio State adds that foam and caulk must be out of the birds' reach.

AI-generated

Where the openings go

The sources agree on four placement rules.

1. High, near the roof or ceiling

   Maryland asks for a vent or opening near the roof or ceiling so that ammonia and stale air can escape. Wisconsin mentions a vent on top of the house or a window left open a little.

2. Away from the prevailing wind

   Penn State Extension and the University of New Hampshire Extension both place openings on the side away from prevailing winds. Penn State names the south or east side as usually best.

3. Never directly over the roost

   Penn State asks that vents or windows do not open directly over the perching area. If the only possible vent position is above the roost, move the roost.

4. An inlet and an outlet if you can

   Wisconsin describes the ideal as an inlet and an outlet, so that air moves through the house without it being drafty. Penn State suggests angling inlets upward, so that incoming air mixes with the warmest air first.

Cover every opening with sturdy wire or screen. Wisconsin reminds keepers that raccoons and other predators squeeze through fairly small holes, and that winter makes them hungry. New Hampshire mentions vent holes or a small window covered with burlap as a simple version.

How much is enough?

Guides often quote a vent area per bird. We looked for such a figure in the extension publications listed below and found none for a backyard coop, so this page gives none.

What the sources offer instead is a size class and a test. Penn State Extension says that for small coops, windows or vents on one side of the house usually provide plenty of ventilation. And three signs tell you when it is not enough:

If you see one of them, increase ventilation. If you see birds huddling and fluffing up while air visibly moves at roost height, the opposite problem exists. New Hampshire advises checking in that case whether the coop needs sealing against wind or whether the ventilation lets in too much airflow.

Typical winter mistakes

Wrapping the coop to the roofline. A heavy plastic tarp over open wire sides blocks wind at ground level, and Ohio State recommends it as a temporary wall. The same fact sheet warns that the sides must not reach roof level, because that stops ventilation and lets moisture build up. This matters for winterizing a chicken coop. More on covers under winter covers for coops and runs.

Insulating without ventilating. Penn State states that well-ventilated houses also need insulation and a vapor barrier, and that failing to insulate or ventilate properly leads to moisture on walls and ceiling in cool weather. Insulation and ventilation work together. An insulated chicken coop with its vents closed is a damp coop.

Deep bedding left wet. Deep, dry bedding insulates. Ohio State notes that it can also increase humidity and asks keepers to check the moisture level in the coop daily and to mix or fluff the bedding. Wisconsin's rule: remove obviously wet areas, leave dry bedding in place. The method itself is described under the deep litter method.

A leaking waterer inside the coop. Ohio State asks keepers to check waterers for leaks, because they add to the humidity. A heated chicken waterer that sits level and does not drip keeps the litter around it dry.

Closing vents because a heater is running. Wisconsin is explicit that ventilation stays important whether heat is provided or not. If you are weighing a heater, the two camps among the extension services are laid out under do chickens need heat in the winter. A radiant panel heater warms the birds next to it and leaves the air alone, so it does not change how much ventilation the coop needs.

Building or siting a coop with ventilation in mind

For readers who are still planning, Penn State's housing guide adds a few points that reduce moisture before any vent does:

• Build on a high, well-drained spot, so that the floor and run do not stay damp.
• Face the front, the windows and the run to the south, so that the sun warms and dries the coop.
• Give the birds enough space. Fewer birds per area keep humidity down.
• Use sliding windows rather than ones that swing in or out, so that birds cannot roost on them.

Maryland adds that deciduous trees shade the coop in summer and let the sun through in winter.

What this means for the rest of the winter setup

Ventilation is the measure with no running cost and no device to plug in, and the sources put it ahead of heat. When the coop is dry and the roost is out of the draft, the question of how cold is too cold becomes much less pressing. The signs of cold stress are described under how cold is too cold for chickens. Everything else on this site starts from the chicken coop heater home page.