Humidity in Close House Poultry Barns: Why It Matters and How to Lower It

Most producers watch barn temperature daily. Far fewer watch humidity with the same discipline — yet the two together decide whether birds can shed heat at all.

Humidity is what makes two barns at the same 30 °C produce very different results.

Why humidity decides

Birds do not sweat. Once the air is already hot, their only route to shed heat is evaporating water from the respiratory tract — which is what panting does.

Evaporation only happens if the air has room to hold more water vapour. At 50% relative humidity there is plenty of room. At 85% that room is nearly gone, and panting stops cooling effectively.

So at the same temperature, birds in a humid barn are under far more strain than birds in a dry one. Identical thermometer reading, different bird.

Where barn humidity comes from

Four sources, three of them unavoidable:

• Bird respiration. Every breath releases water vapour. A large flock in a sealed space produces a significant volume.
• Litter. Manure holds water that evaporates continuously into the barn air.
• Drinker spillage. Leaking nipples or excessive water pressure add water to the litter.
• Evaporative cooling. Pads and misting raise humidity — that is how they work.

That fourth source is the one that often creates a new problem while solving an old one.

Reference limits

Ranges commonly used as a reference in broiler housing:

Phase	Reference humidity
Brooding (week 1)	60–70%
Weeks 2–3	55–65%
Week 4 to harvest	50–65%

Every strain guide publishes its own figures, so follow the guide for the cross you run.

Worth understanding: the upper limit is not absolute — it depends on temperature. 70% at 24 °C is unremarkable. 70% at 32 °C is a stressed environment.

During brooding, humidity that is too low is also a problem — dry air dehydrates chicks and raises dust.

Signs humidity is too high

Before a sensor gives you a number, the barn tells you:

• Litter cakes and feels sticky underfoot rather than friable
• Ammonia smell strengthens — wet litter is where ammonia is produced
• Condensation on walls, ceiling or metal surfaces in the morning
• Birds keep panting even when temperature reads within range
• Respiratory problems increase across the flock

The last is the costly one. Ammonia damages the respiratory lining, opening the way for secondary infection.

How to lower humidity

1. Increase air exchange

The most direct route. Drier outside air comes in, humid air goes out. In a close house this means raising the minimum ventilation rate.

The limit: during the rainy season the outside air may already be humid, so air exchange delivers less. And raising ventilation at night can pull temperature below target.

2. Manage the litter

Wet litter is the most controllable humidity source:

• Check for nipple leaks routinely — one leaking line can wet a large area
• Set drinker pressure appropriate to bird age
• Top up or turn litter where it starts caking
• Make sure drainage around the barn does not run water inward

3. Run evaporative cooling on sensors, not a timer

This is where it most often goes wrong. Pads and misting raise humidity. On a fixed timer, the system keeps running on days that are already humid — dropping temperature a few degrees while pushing humidity into the zone that blocks the birds from shedding heat.

Correct control weighs both: the system stops at a humidity threshold even if temperature is still above target. There is a point past which more cooling does harm.

4. Choose a cooling method with the right droplet size

Not all evaporative cooling adds humidity load the same way.

Low-pressure fogging (3–15 bar) produces droplets of 50 microns and up. Droplets that size do not fully evaporate in the air — some land on the litter. Water that lands on litter cools the air not at all, yet still evaporates slowly through the day, raising humidity with no cooling benefit in return.

High-pressure misting (70 bar) produces sub-10-micron droplets that evaporate in the air. Humidity still rises — that is unavoidable — but every litre used actually produces cooling, and the litter stays dry.

The difference: for the same humidity load, a high-pressure system delivers a far larger temperature drop.

Temperature and humidity must be read together

The most common mistake is managing them separately — targeting temperature with ventilation and cooling, then checking humidity occasionally.

What the bird experiences is the combination. Some operators use a combined temperature-humidity index for this, but the practical principle is simple: the higher the humidity, the lower the temperature you need to target for birds to stay comfortable.

If barn humidity sits above 80% through the afternoon, the temperature target has to come down — and at that point evaporative cooling becomes less effective, because the air is already near saturation.

In short

Humidity is not a secondary variable behind temperature. Together they decide whether a bird can shed heat.

Measure both, at bird level, at several points along the barn. Manage litter as the most controllable source. And run evaporative cooling under sensor control — a system that does not know when to stop can make a humid day worse.

See poultry house cooling with sensor control. For a calculation for your barn, send dimensions, housing type and flock size over WhatsApp.