GuideCoop · concept

Chicken coop ventilation vs draft

Ventilation and drafts are both airflow. The difference is where the air enters and exits relative to the birds. Air moving above the roost (out through the high vent) and below it (in through the low intake) is ventilation — it exchanges the coop volume without putting wind on the flock. Air crossing horizontally at perch height is a draft — it strips body heat from birds trying to stay warm.

The same volume of air can be either. Move a wall vent from mid-height to the gable peak and the airflow becomes ventilation. Add a low intake without a kickplate and the ventilation becomes a draft. Beginners commonly conflate the two — “my coop has too much airflow, it's drafty” — and seal the coop in response, which traps moisture and causes frostbite.

Definitions worth pinning down

Ventilation — continuous controlled airflow that exchanges the coop volume to remove ammonia, CO₂, and moisture. Required year-round, including the deepest cold. Driven by stack effect (warm air rises and exits high; cool air enters low) and optionally augmented by fans. Properly designed ventilation routes air around the birds, not across them.

Draft — uncontrolled airflow at perch height that puts moving air directly on roosting birds. Strips body heat the birds are using to thermoregulate. Common causes: mid-wall vents placed at roost height; low intakes without kickplates; gaps in the wall framing at perch level.

Both are airflow, but the consequences split sharply. Ventilation keeps birds healthy through winter. Drafts drop lay rate, raise feed consumption, and elevate disease susceptibility through chronic energy stress.

The diagnostic test

On a calm cold night with the flock roosting, stand inside the coop at perch height — about 18–24 inches off the floor. What do you feel?

Air moving on your face/neck at that height: draft. Find the offending opening (usually a mid-wall vent or a low intake without a kickplate). Move it higher, lower, or add a baffle.
Air still, no perceptible movement: either properly ventilated (warm humid air rising silently to the high vent above your head) or under-ventilated (no exchange at all). Check for condensation on the roof, frost on interior surfaces, ammonia smell — those tell which one.
Air slightly moving up, away from you: properly ventilated. The convective lift over the roost is carrying moist air toward the high vent. This is what you want.

Common draft sources (and the fix for each)

Mid-wall vent placed at perch height. Move it up to gable-peak level (eyebrow vent, gable louver) or down to floor level (low intake). Same vent area, different position; ventilation instead of draft.
Low intake without a kickplate. Add a 12-in solid kickplate above the intake (interior side). Wind entering at the floor still drives stack-effect intake but is deflected up over the kickplate and behind the birds rather than across the floor.
Drafty pop-door at perch height. Most pop-doors are below perch level by design — but coops with elevated floors put the pop-door right at perch height. Add an internal vestibule or move the roost to a different wall.
Plank gaps in the wall siding. Wood-shrinkage gaps in an aging coop. Caulk the perch-level gaps; leave the high and low gaps as they are (free vent area).
Cracked window glass at roost height. Replace the glass or reframe with a hardware-cloth-screened opening and shutter.

The trap: sealing the coop to stop drafts

When a beginner identifies a draft, the instinct is to seal the coop tighter overall. The instinct is wrong. Sealing the coop traps moisture (ammonia, CO₂, water vapor from respiration and droppings), which condenses on cold interior surfaces and produces wet frostbite on combs and wattles. The bird suffers more from the sealed coop than from the original draft.

The fix is geometric, not sealing. Identify which opening is putting air at perch level. Move it above or below the perch line. Keep the total vent area at the calculated baseline for your coop size + climate. The result is the same airflow volume routed correctly — ventilation instead of draft.

Run the math for your coop

The high/low split is what determines whether your vent area becomes ventilation or risks becoming a draft. Cold climates want ~70% high, 30% low (more high so warm humid air can escape; less low so cold drafts don't cross the floor). Temperate runs 50/50; hot/humid runs 60/40.

The coop ventilation calculator outputs the high/low split for your specific climate alongside the total vent area. Use those numbers to size individual vent openings — the geometry is the answer to the ventilation-vs-draft question.

Frequently asked

What is the difference between ventilation and a draft in a chicken coop?

Both are airflow. Ventilation is air moving above and below the birds — high outlet and low intake — that exchanges the entire coop volume continuously without putting wind directly on the flock at perch level. A draft is air blowing horizontally across roost height, which strips body heat from birds that are trying to thermoregulate. Same volume of air can be ventilation or a draft depending entirely on where it enters and exits.

How do I tell if my coop has a draft problem?

Check on a calm cold night with the flock roosting. If you can feel air movement standing at perch height — about 18–24 inches off the floor — the coop has a draft. The fix is closing or shifting the opening that's putting air at that height: usually a wall vent placed too close to roost height, or a poorly-positioned low intake without a kickplate. Move the offending opening higher or lower, never seal the coop tighter overall.

Does winter ventilation cause drafts?

Only if vent placement is wrong. Properly placed winter ventilation (high outlet near the peak + low intake at floor level behind a kickplate) moves air over and under the birds without crossing them at perch height. The common cause of winter drafts is a single mid-wall vent — air enters or exits at exactly roost level. Either move the vent above or below the roost line, or add a baffle that redirects the airflow.

Can my chickens get sick from drafts?

Drafts don't make birds sick directly — chickens don't catch colds from cold air the way humans associate sickness with chills. What drafts do is force birds to spend metabolic energy on warmth instead of growth or laying. A drafty coop in cold weather drops lay rate and feed efficiency before it shows visible distress. The downstream risk is that energy-stressed birds become more susceptible to actual pathogens (Mycoplasma, infectious bronchitis), so chronic drafts indirectly elevate disease risk.

Should I block all drafts in winter?

Block drafts at perch height; keep vents fully open at the right heights. The two are not the same action. Adding a kickplate above a low intake to block ground-level wind from crossing the floor is correct. Sealing the high vent because cold air is leaving is wrong — it traps moisture. Identify which openings are putting air at perch level (drafts) vs which are putting air above or below (ventilation), and only modify the draft-makers.

What temperature is too cold for chickens without supplemental heat?

Adult standard-breed layers handle ambient temperatures down to about 0°F (–18°C) without supplemental heat in a properly ventilated, dry, draft-free coop. Cold-hardy heritage breeds (Buckeye, Wyandotte, Chantecler) handle colder. The ambient threshold matters less than the dryness and the absence of perch-level drafts; a hen at –10°F dry handles it better than a hen at +25°F damp with a draft across the roost.

By Jimmy L Wu. Reviewed 2026-05-01. Ventilation principle (must remove ammonia, CO₂, moisture without putting drafts on birds) anchored on OSU Extension EC-1644 and UMN Extension. The high/low vent split percentages are HatchMath methodology grounded in stack-effect physics. Not veterinary advice — for sick birds or any animal-health emergency, consult an avian or livestock veterinarian, or your county Cooperative Extension office.