Short answer: An egg incubator is a sealed box that holds eggs near 37.5 °C, keeps humidity in a set band, turns the eggs several times a day and swaps stale air for fresh. Each of those four jobs belongs to one or two parts, and those parts are the ones that fail. If you know what each part does, you can tell which job went wrong before you blame the eggs.
Key takeaways
- A machine copies four things a broody hen does: heat, moisture, turning and fresh air.
- The thermostat reads the air where its sensor sits, so check the temperature at egg height.
- Water trays set the humidity and vents fine-tune it. Change the water first, the vents second.
- Turning stops the embryo sticking to the membrane. Switch it off at lockdown, not before.
- Most failures come from one part that stopped working quietly, such as a dusty fan or a drifting sensor.
Start from the broody hen, not the box
A broody hen sits on her clutch for three weeks and never once looks at a thermometer. She keeps the eggs warm, keeps them just damp enough that the shell does not dry out, shifts them a few times a day and steps off often enough to let fresh air in. An incubator is a box built to do those same four jobs on a timer.
That comparison is more useful than it sounds. When a hatch fails, one of those four jobs was not done properly, and each job belongs to a specific part of the machine. Most growers who lose a setting never work out which job failed. They change the supplier, change the feed and blame the eggs, and the next setting fails in the same place.
The machine does not make chicks. It holds conditions steady while the embryo makes itself, and the better you understand the parts doing the holding, the less you have to guess. If you are still choosing a machine, our beginner's guide to buying an incubator covers size and features.
The parts you will find in almost every machine
Cabinet machines and digital ones look different on the outside, but the inside layout is much the same. The table lists what sits in there, what each part is for and how it usually fails.
| Part | What it does | How it usually fails | How you notice |
|---|---|---|---|
| Heating element | Puts heat into the air | Burns out, or the controller stops calling for heat | Temperature sinks slowly over hours, not all at once |
| Fan | Moves warm air across all trays | Dust builds up on the blades, or the motor wears | Top and bottom trays read different temperatures |
| Thermostat, controller and sensor | Switches the heater on and off | Sensor sits in a dead spot, or dust covers it | The display and the reading at egg height disagree |
| Water trays or wicks | Supply the moisture | Run dry, or grow green slime | Humidity falls over two or three days with nothing else changed |
| Egg turner | Tilts the trays or rack on a timer | Gears wear, or the rack jams | Marked eggs stay on the same side after a turn |
| Vents | Let stale air out and fresh air in | Left shut, or left wide open | Humidity swings, and the room smells of the machine |
| Hygrometer | Reads the moisture in the air | Drifts out of calibration | The reading never moves, even after you add water |
A failure rarely announces itself. Most parts give a small, quiet warning before they stop, and the warning is usually a number that stopped moving or started drifting. Write the readings down each morning and evening. A slow drift shows up in a log long before you would notice it by looking.
How the heater and thermostat keep the egg steady
The thermostat is a simple loop. When the air falls below the set point, the heater comes on. When the air climbs above it, the heater goes off. A good machine does not hold a perfect line. It rises a fraction above the set point, falls a fraction below and repeats that pattern all day. If the swing stays within half a degree either side, you are in good shape.
Where the sensor sits matters more than most people expect. A sensor right beside the element reads higher than the eggs really are, so the machine switches off while the trays are still cool. A sensor tucked in a corner, or hidden behind a tray, reads a calm spot that may be a long way from the egg. Put the sensor at about the height of the top of the eggs, in the middle of the load, and keep it clear of anything that touches it.
The room matters too. On a still afternoon in the dry season, the air indoors can feel very hot, and the heater has to work less. In the cooler harmattan mornings it works harder, and that is when a weak element or a dusty fan shows itself. If your display reads a steady 37.5 but the eggs feel cool when you lift the lid for a moment, believe the eggs for now and go and check the sensor. For the daily targets, keep our temperature and humidity chart beside the machine.
Heat speeds the embryo up, but only within a narrow band. That is why we treat the set point as a target to hold, not a number to push. A machine running a little hot to hurry things along is working against the chick, and the damage does not show until the hatch.
What the fan does, and why still air needs care
Warm air rises. In a still-air machine the top of the cabinet runs warmer than the bottom, and the trays nearest the heater run hotter than the rest. That is why still-air machines are usually run with a lower display setting, and why you must read temperature at tray level, not just at the top of the cabinet.
A fan evens the heat out, but it does two other things at the same time. It speeds up evaporation off the water trays, and it pulls dust through the machine. A clean fan guard is part of your temperature control and your humidity control at once. When the fan slows, the top trays heat up while the bottom trays fall behind, and the controller cannot see the difference because the sensor sits somewhere in the middle.
We would rather a grower run a simple machine they can keep clean than a complicated one they treat as a black box. Whatever you buy, learn where the fan is, how it turns and what its blades look like on a dusty day.
Where the humidity really comes from
Humidity in an incubator is water evaporating into the air. Three things decide how much: the temperature of the water, the area of water exposed to the air, and how much air is exchanged through the vents. Warm water spread over a wide surface gives you a lot of moisture. Cold water sitting in a small tray gives you very little.
This is why the first thing to adjust is the water, not the vents. Doubling the wet surface with sponges or a wider tray lifts humidity steadily without changing the air exchange. Opening a vent drops humidity quickly and also lets in drier room air, so it is a blunt tool and needs small steps.
Top up with water at room temperature rather than straight from the fridge. Cold water pulls the air temperature down for a while, and the humidity reading wobbles, which makes it hard to see a clean trend.
Keep the water clean. Green slime in a tray means algae and bacteria have settled in, and that water is not doing the job you think it is. Empty, scrub and refill the trays on the schedule in our cleaning and disinfecting guide, which covers the routine in more detail.
Why the egg has to move
Left still for three weeks, the embryo can settle against the inner membrane of the shell and stick to it. Turning keeps the yolk moving and the embryo free. A tilt of about 45 degrees each way is the common setting. Automatic turners usually move every hour or two, and that is the rhythm we would pick for a home machine.
Turning stops at lockdown, around day 18. Turn after that and you risk shifting a chick that has already moved into hatch position. That is the one point where you switch the turner off and leave it off.
Test a turner before you trust it. Pencil a dot on the top of three eggs, set them in the machine, and check after one full cycle that the dots have moved. If they have not, the rack is jammed, the gear is worn or the timer is switched off. Fix that before anything else, because a turner that looks busy but does not move the eggs is worse than no turner at all.
How the embryo breathes through the shell
The shell looks solid, but it is full of tiny pores. Oxygen passes in and carbon dioxide passes out. Early in incubation the embryo needs very little, so the pores do their job without help. In the second half of the 21 days the chick is large and its demand for oxygen climbs steeply.
Fresh air comes from the vents. A closed machine in a warm room can run short of oxygen late in the hatch and build up carbon dioxide. That shows up as chicks that pip but cannot finish. Many growers open the vents a little from about the second week and wider in the final days, but the timing depends on your machine and the season. Follow the instructions that came with yours, and watch the chicks.
Vents and humidity pull against each other. A vent opened to clear carbon dioxide also drops the humidity, so every change to ventilation needs a check on the hygrometer the next day. Our guide on fixing humidity problems walks through that balance in detail.
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What the machine is doing across the 21 days
The embryo does not move through the 21 days at a steady pace. Most of the visible change comes in the last third, which is why growers think a quiet first week means nothing is happening. A lot is happening under the shell.
- Days 1 to 3: the body plan forms, and the heart begins to beat within the first two days.
- Days 4 to 7: blood vessels spread over the yolk, and the first feather buds show by about day 7.
- Days 8 to 14: bones harden, the legs and wings take shape, and the chick grows quickly.
- Days 15 to 18: the chick fills more of the shell, and by about day 18 it turns to face the air cell.
- Days 19 to 21: the chick pips the membrane, breathes from the air cell and works its way out.
Other species keep their own clocks. Guinea fowl and turkey eggs take 28 days, so the settings and turning routine you learned on chicken eggs need changing. Do not run a 28-day species on a 21-day plan and expect the timings to line up. Our candling guide shows what a healthy egg should look like at each check, and it is the quickest way to see the clock working.
Setting the machine up for Ghana's room
Where you put the machine decides how hard it works. Keep it out of direct sun, away from a window that catches the afternoon and away from a kitchen stove or a charcoal fire. Heat from outside reaches the machine through the walls and pushes the heater into longer runs.
The harmattan brings fine dust from December to February, and it goes straight into fans, vents and sensor housings. If your room cannot be closed, cover the machine on the dustiest mornings, and wipe the fan guard every week during harmattan rather than every month. A dusty fan is one of the most common reasons growers tell us a machine has suddenly started running hot.
Rats and lizards are a problem on many farm rooms. Cables get chewed, and a warm cabinet looks like shelter to small animals. Keep the plug off the floor and the cable clear of the back panel.
Give the machine its own socket where you can, and do not share it with a kettle or a grinder. Power supply in Ghana varies from place to place and from week to week, so plan the backup properly. Our guide on incubating through power cuts covers the options.
A check to run before you trust a machine
Before the first egg goes in, put the machine through a short test. A new machine needs this, a machine that has sat in a store room needs it, and any machine that has been moved needs it too.
- Place a calibrated thermometer at egg height in the middle of the tray, and a second one near the top corner.
- Switch on and let the machine run empty for at least 24 hours.
- Record both readings every two hours on the first day, then twice daily.
- Check the swing. If the temperature stays within half a degree of the set point, carry on. If it swings wider, check the sensor position before you touch the controller settings.
- Watch the turner through one full cycle and confirm the marked eggs have moved.
- Fill the water trays and confirm the hygrometer climbs into your target band within a day or two.
- Listen to the fan. A rattle or a grinding noise means it needs cleaning or replacing before any eggs go in.
If a step fails, fix it and start the test again from the beginning. A machine that passes on Monday and fails on Thursday is usually a loose connection, a sensor that has moved or a fan that has picked up dust. None of those show up if you only test once. Once the machine passes, setting day is the next thing to get right.
Three things a machine cannot do
A machine cannot pick good eggs. It keeps conditions steady for whatever you put in, and a cracked, dirty or badly stored egg will still fail on perfect settings. The choice happens before the egg reaches the machine. If you are buying fertile eggs, read our guide on choosing fertile eggs for hatching first. If a hatch still fails, why eggs don't hatch explains how to read the dead ones.
A machine cannot make up for heat. More temperature speeds the embryo up but does not make the chick any better. Running the machine hot to hurry the hatch is one of the fastest ways to lose a whole setting, and we see it most often in the first week of a hot spell.
A machine cannot replace checking. Open it when you must, read the numbers when you can, and remember that every time you lift the lid the air inside changes. The grower who reads the log twice a day usually does better than the one with the most expensive controller. If you want a second pair of eyes on your readings, send us a photo of the log on WhatsApp at +233 24 915 1503. If you would rather skip the machine and buy ready chicks, start on our day-old chicks page or send your order through the order form.
Questions farmers ask
Does an incubator hatch eggs on its own?
Not in the sense most people mean. It keeps heat, moisture, turning and air exchange steady, and the embryo does the rest. A machine that is set up and run well gives the egg its best chance, but it cannot rescue an egg that was damaged, stored badly or poorly fertilised. Think of it as a controlled room, not a replacement for the hen.
Why does the thermometer read differently from the egg?
The sensor reads the air where it sits, and the egg warms and cools more slowly than the air around it. Position matters: a sensor beside the heater reads high, and one in a cold corner reads low. Check with a second thermometer at egg height, and fix the sensor position before you change the controller setting.
Do I need a fan in my incubator?
A fan keeps the temperature even across all trays. Without one, the top runs hotter than the bottom. Still-air machines can work well if you manage the gradient and read the trays at egg height. Forced-air machines are easier to keep even, but the fan needs cleaning and checking, because dust on the blades changes the temperature as well as the humidity.
How often should the eggs be turned?
Automatic turners usually move the eggs every hour or two, and that rhythm suits most growers. Hand turning should happen at least three times a day, and more often is better if you can manage it. Stop turning at lockdown, around day 18, and keep the machine closed while the chicks finish hatching.
Why do vents matter if the water controls humidity?
Water adds moisture and vents remove it. Vents also bring in fresh air and let out carbon dioxide, which the embryo needs for breathing. Adjust the water first when humidity is off, because opening a vent to lower humidity also changes the oxygen balance. Make vent changes in small steps and check the hygrometer the next day.
Can I use a bulb or a room heater instead of a proper machine?
You can make a box warm with a bulb, but you cannot make it steady. Bulbs and room heaters have no sensor working from egg height, and they often run hot on one side. A purpose-built machine gives you a sensor, a fan and a turner that work together. If money is tight, buy a smaller machine you can control rather than a larger box you cannot.
How do I know the machine is ready before I set eggs?
Run it empty for at least 24 hours with water in the trays, and check that the temperature stays close to the set point at egg height. Confirm the turner moves marked eggs and the hygrometer climbs to the band you want. If you want a second opinion on your readings, send us a photo of the log on WhatsApp at +233 24 915 1503.
