Broiler House CO2 and Ammonia: The 3,000 ppm and 20 ppm Limits, and How to Monitor Them
TL;DR: In England, conventionally reared meat chickens may be stocked above 33 kg per square metre, up to 39 kg, only if extra conditions in Schedule 5A of the Welfare of Farmed Animals (England) Regulations 2007 are met. Each broiler house must then keep ammonia below 20 ppm and carbon dioxide below 3,000 ppm at the level of the chickens’ heads, limit inside temperature in hot weather and cap average humidity in cold weather. CO2, temperature and humidity can be logged continuously at bird height; ammonia needs its own instrument.
Last updated: 14 September 2026
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Key takeaways
- In England, a broiler house can be stocked above 33 kg per m², up to 39 kg per m², only if the extra conditions in Schedule 5A of the Welfare of Farmed Animals (England) Regulations 2007 are met.
- Those conditions require ammonia below 20 ppm and carbon dioxide below 3,000 ppm, measured at the level of the chickens’ heads.
- When it is above 30°C outside in the shade, the inside must not be more than 3°C warmer than outside.
- When it is below 10°C outside, average relative humidity inside over 48 hours must not exceed 70%.
- CO2, temperature and humidity can be logged continuously. Ammonia needs a separate instrument.
What are the air quality limits for a broiler house?
The air quality limits for a broiler house in England are set out in Schedule 5A of the Welfare of Farmed Animals (England) Regulations 2007, which covers conventionally reared meat chickens. The stocking density must not exceed 33 kg per square metre of usable area, unless the keeper meets extra requirements, in which case up to 39 kg per square metre may be used.
Those extra requirements include a ventilation system, with heating and cooling if necessary, designed, built and operated so that the following limits are met.
| Condition in Schedule 5A, paragraph 5 | Limit |
|---|---|
| Ammonia at the level of the chickens’ heads | Must not exceed 20 ppm |
| Carbon dioxide at the level of the chickens’ heads | Must not exceed 3,000 ppm |
| Outside temperature in the shade above 30°C | Inside no more than 3°C above outside |
| Outside temperature below 10°C | Average inside relative humidity over a continuous 48 hours no more than 70% |
The keeper must also keep documentation that includes a ventilation plan with target air quality parameters, alarm and backup systems for equipment essential to the chickens’ health and wellbeing, and records of technical inspections of the ventilation and alarm systems. Check the conditions that apply to your own broiler house, stocking density and nation.
Why measure CO2 at bird height?
Measure CO2 at bird height because that is where the regulations measure it: at the level of the chickens’ heads. A sensor on a roof truss or by the control room door reads different air from the air the birds breathe.
Height is not fixed through a crop. Birds grow quickly, so sensors on adjustable brackets or chains can be raised as the flock grows, keeping readings at head level from placement to depopulation.
Position along the broiler house matters too. Ventilation is not always even from one end to the other, so a single sensor can show a well-aired end while the other is stale. One CO2 sensor at each end is the practical minimum.
What does the 70% humidity rule mean in practice?
The humidity rule is an average, not a single reading. When the outside temperature is below 10°C, average relative humidity inside the broiler house over a continuous 48 hours must not exceed 70%. A reading of 80% for an hour does not break it on its own; two days that average above 70% does.
That makes continuous logging the only practical way to know where you stand. A rolling 48-hour average needs a reading every few minutes, day and night, from sensors spread along the house, and it needs the outside temperature too, because the rule only applies when it is below 10°C.
How does the 30°C rule work?
The 30°C rule compares inside with outside. When the outside temperature measured in the shade exceeds 30°C, the inside temperature must not exceed the outside temperature by more than 3°C. On a 32°C afternoon, the broiler house must stay at or below 35°C.
That means a heat record needs two readings, not one. Temperature sensors inside show the house, but only a sensor outside in the shade shows whether the rule is in force and what the limit is. A monitoring kit for a broiler house should include one outside temperature sensor, mounted in shade, alongside the sensors inside.
What about ammonia?
Ammonia has its own limit of 20 ppm at the level of the chickens’ heads, and it needs its own measurement. The CO2, temperature and humidity sensors described here do not measure ammonia, so a broiler house still needs a suitable ammonia instrument and a routine for using it.
The Government’s code of practice for the welfare of meat chickens, which applies in England, says measurements of CO2 and NH3 should be taken when there is a risk of excessive build-up.
CO2 and ammonia are linked through ventilation in a broiler house, since both build up when fresh air does not reach the birds, but one cannot stand in for the other. A good CO2 record shows whether ventilation is keeping up; it does not prove ammonia is below its limit.
How accurate does a CO2 sensor need to be?
A CO2 sensor for a broiler house needs a range above 3,000 ppm and an accuracy you can build a margin from. The Milesight EM500-CO2 measures 400 to 5,000 ppm with an NDIR sensor, to ±(30 ppm + 3% of reading) between 0°C and 50°C and 0 to 85% relative humidity.
At 3,000 ppm that tolerance works out at ±120 ppm, so set an alert comfortably below the limit, for example at 2,500 ppm, to leave time to adjust ventilation before the limit is reached. Note that the accuracy specification stops at 85% relative humidity, which a humid house can exceed.
What are the limits of monitoring?
Monitoring records the air in a broiler house; it does not ventilate it. Four limits are worth planning around.
- No ammonia. The sensors here do not measure it. Use a suitable instrument.
- No control. Sensors alert; they do not run fans, inlets or heaters, and they do not replace the house controller’s own alarms or the alarm and backup systems the regulations expect. The code of practice notes that backup systems must be thoroughly inspected, and the alarm tested, at least once every seven days.
- Dust. Dust and ammonia shorten the life of electronics. Clean the housings between flocks and check CO2 readings against fresh outdoor air.
- Radio through steel. Mount the gateway on the outside wall or in the control room doorway, and test the signal from inside the house.
What does a broiler house monitoring kit include?
A broiler house monitoring kit needs a gateway with its own mobile connection, CO2 sensors at each end and temperature and humidity sensors along the house. Our poultry house monitoring kit combines a UG65 gateway with 4G, two EM500-CO2 sensors and two EM300-TH sensors, with live prices and one click to the basket. For the 30°C rule, add one more EM300-TH outside in the shade.
For the wider CO2 range, see our guide to LoRaWAN CO2 sensors, and for other farm uses, industrial IoT for agriculture.
Frequently asked questions
What is the CO2 limit in a broiler house?
Under Schedule 5A of the Welfare of Farmed Animals (England) Regulations 2007, houses stocked above 33 kg per square metre must keep carbon dioxide below 3,000 ppm, measured at the level of the chickens’ heads.
What ammonia level is allowed in a broiler house?
The same conditions require ammonia not to exceed 20 ppm at the level of the chickens’ heads.
When do the 3,000 ppm and 20 ppm limits apply?
They are part of the requirements for keeping conventionally reared meat chickens in England at stocking densities above 33 kg and up to 39 kg per square metre of usable area.
Do I need an outside temperature sensor?
Yes, if you want to evidence the heat rule. It applies when the outside temperature in the shade exceeds 30°C, so you need a shaded outside reading to know when it is in force.
Can a CO2 sensor measure ammonia?
No. CO2 sensors measure carbon dioxide only. Ammonia needs its own instrument, even though both rise when ventilation falls short.
Keep the record the rules describe
A broiler house at higher stocking density has four limits to meet, and two of them are measured at the level of the chickens’ heads. Log CO2, temperature and humidity continuously at bird height, add a shaded outside sensor, and keep ammonia checks on their own routine.
See the poultry house monitoring kit with live prices, or send us the number and length of your houses and an engineer will plan the sensors within one working day.
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