Coop Ventilation in Winter: Sealed Is Not the Same as Draught Free

The most common winter mistake is closing everything up to keep the flock warm. It feels right. It is also the fastest way to give a healthy hen frostbite.

Frostbite comes from moisture, not cold

A hen exhales a surprising amount of water vapor overnight, and the droppings underneath the roost release more. In a sealed coop that moisture has nowhere to go. It settles on combs and wattles, and wet tissue freezes at temperatures that dry tissue shrugs off. Keepers in Minnesota with open-front coops routinely come through winter with cleaner combs than keepers in far milder states who sealed every gap in October.

The problem you cannot see

Ammonia from droppings builds up in still air. If you kneel down to roost height and your eyes sting, your birds have been breathing that all night. It damages the lining of the airway and opens the door to respiratory infection, which is a far bigger winter killer than cold ever is.

What good ventilation looks like

High and permanent. Vents belong above the level of the roosts so that air moves out over the birds rather than across them. A common rule of thumb is roughly one square foot of permanent vent for every ten square feet of floor. Leave it open in January. Yes, really.

A draft is a different thing. That is moving air at bird level, blowing directly on a hen who is trying to sleep. That you block. Anything above their heads you leave alone.

Two checks you can do tonight

Go out after dark with a flashlight. If the inside of the window or the underside of the roof is beaded with condensation, the coop is too tight. Then crouch down to roost height and breathe in. If it smells sharp, you need more ventilation, fresh bedding, or both. Running deep litter? Here is how to keep deep litter from turning into an ammonia problem.

💡 If you are cutting a new vent, cover it with hardware cloth, not chicken wire. A raccoon can tear chicken wire apart with its hands, and a vent is exactly the kind of opening it will test.

More on the mesh that actually holds: hardware cloth, the right way to use it.