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New keepers often build tight, cozy coops to keep hens warm. Then the bedding turns damp, the air stings the eyes, and combs get frostbite in winter. The coop was not too cold. It was too closed.
What ventilation has to remove
Chickens breathe out moisture all night, and their droppings add more. The Extension Foundation’s poultry program notes that chickens generate a great deal of moisture from breathing, droppings and spilled water, and that ventilation is needed to stop moisture and ammonia from building up.
Ammonia comes from droppings breaking down in wet bedding. If you can smell it at your height, it is stronger at the birds’ height.
Ventilate high, block drafts low
Oregon State University Extension says a well-designed coop has adequate air exchange without creating drafts, and that passive ventilation through openings such as windows or vents in gables, eaves or roofs is adequate for most backyard coops.
- Place vents near the roofline, above the roosts, so warm moist air rises out.
- Keep openings away from roosting birds so air does not blow on them at night.
- Cover every vent with hardware cloth so it is not a way in for predators.
- Add more openings for summer that can be closed partway in winter.
- Use fans only in heat, and never pointed straight at the birds.
Signs you need more air
- Condensation on windows, walls or the underside of the roof
- Ammonia smell when you open the door
- Damp, caked bedding that stays wet
- Frostbite on combs and wattles in winter
- Respiratory signs such as sneezing or wet eyes
A cool coop with good airflow is healthier than a warm, sealed one. Oregon State notes coops do not need insulation, but they should be free of drafts.
The bedding guide addresses moisture at floor level. The winter care guide puts airflow alongside cold-weather routines.
Questions people ask
How much ventilation does a chicken coop need?
Enough that there is no condensation or ammonia smell, without drafts on the roosting birds. Most backyard coops manage with passive vents high on the walls.
Should I close the coop vents in winter?
Not completely. Close drafts at bird level but keep high vents open so moisture can escape.
Why does my chicken coop smell of ammonia?
Droppings are breaking down in damp bedding. Improve ventilation, remove wet bedding and add fresh, dry material.
Do chickens need a window?
Windows help with light and airflow. Cover them with hardware cloth so they are not an entry point for predators.
Where these figures come from
- Living on the Land: Backyard Chicken Coop Design Oregon State University Extension · extension.oregonstate.edu
- Frostbite in Chickens Extension Foundation, Small and Backyard Poultry · poultry.extension.org
Figures last checked September 2026.
