Monitoring Coop Air Quality in Winter: Why Ammonia Builds Up When Coops Are Closed Up

Summer coops benefit from constant natural airflow — open windows, breezy runs, doors propped for ventilation. Winter changes that equation. Coops get sealed up tighter against the cold, and that same closed-up environment that keeps birds warmer also traps ammonia, moisture, and airborne particulates far more effectively than most keepers realize.

Why Ammonia Is a Bigger Problem in Winter

Ammonia builds up from decomposing droppings, and its buildup accelerates in warm, moist, poorly ventilated conditions — exactly the environment a well-intentioned but over-sealed winter coop can create. Chronic ammonia exposure damages the respiratory tract lining in chickens, making them significantly more susceptible to respiratory infections throughout the rest of winter — a season when illness is already harder to treat and recover from due to the cold.

Why You Can’t Always Smell the Problem in Time

Human sense of smell adapts to ammonia relatively quickly, meaning levels that are already harmful to chickens can feel “normal” to you after a few minutes in the coop. Chickens, being much smaller and positioned closer to the bedding (where ammonia concentrates), are exposed to meaningfully higher concentrations than what you perceive standing at coop-door height.

What an Air Quality Sensor Actually Tells You

A dedicated air quality or ammonia sensor gives you an objective reading instead of relying on your nose — critical in winter when you’re less likely to be propping the door open for a “fresh air check” the way you might in summer. Many sensors also track humidity and particulate levels alongside ammonia, giving a fuller picture of coop air conditions at a glance, and some integrate with smart home systems for real-time alerts if levels cross a set threshold.

Practical Signs to Watch Alongside a Sensor

• Watery eyes or nasal discharge in your flock
• Sneezing or open-mouth breathing
• Reduced activity or appetite
• A visible ammonia smell when you first walk in (before your nose adjusts) — if you notice it immediately upon entry, levels are already elevated

What to Do If Ammonia Levels Are High

1. Increase ventilation immediately, even if it means accepting a slightly colder coop temporarily — the ammonia risk to respiratory health outweighs a modest, dry-air temperature drop.
2. Turn or refresh bedding, especially if using the deep litter method, which needs regular turning specifically to manage ammonia buildup.
3. Check for and fix moisture sources — leaking waterers, condensation, or roof leaks all accelerate ammonia production.
4. Reduce stocking density if levels are chronically high — overcrowding is one of the most common root causes of persistent ammonia problems.

Building a Winter Monitoring Habit

Placing a sensor at roost height (where chickens actually breathe, not at your eye level) gives the most accurate real-world reading. Checking it as part of your daily winter coop routine — alongside water and feed checks — turns air quality from a once-a-season concern into an ongoing, easily managed part of flock care. Browse our Air Quality and Sensors collection to add objective monitoring to your winter coop routine.