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Ventilation V/S Humidity

Lets say I built an incubator.(Incubator A) An I put enough vent holes so that the air in the incubator replaced its self every hour. After trial an error I figure out that I have to run my humidity at 40% to get a good hatch rate.
incubator pic
Now lets say I built two more almost identical.

Incubator B: I put in enough vent holes to let the air replace its self every two hours.

Incubator C: I put in enough vent holes to let the air replace its self every 30 minutes.

Now I set all three up side by side at a humidity of 40%.

Three weeks later incubator A starts hatching but B an C has almost none hatch. Why?
egg evaporation
Opening eggs from incubator B you would see very wet drowned chicks.
Opening eggs from incubator C you would find chicks dried out an stuck.

Whats going on here?

When cold air enters the incubator an starts to warm up it starts pulling moisture from anywhere it can find it. Humidity trays an eggs. Everyone knows that bigger humidity trays means less moisture loss from the eggs.

In incubator B the air replaces its self ever 2 hours. As it does it as to absorb X amount of moisture from the eggs.

In incubator A the air is replace every hour. The same X amount of moisture is absorbed each time. So you have twice as much evaporation over 3 weeks as incubator B.

Incubator C replaces the air every 30 minutes. It has twice as much evaporation  as incubator A an 4 times as much as incubator B.

I could run the humidity up to something like 60% in incubator C an I may get good hatch rates. But I'm not fixing the problem I'm compensating for it.

I could also drop the humidity in incubator B to 25% but again I'm not fixing the problem I'm compensating for it.

If you have to run really high humidity to get good hatches your ventilation is to good.

If you have to run really low humidity then you need more ventilation.

That's why no one can agree on the right humidity. Everyone has different ventilation levels. Even with manufactured incubators the difference between having one plug out or two is doubling the ventilation level.

So what about climate? Does the outside air temp an humidity where I live matter?

It does matter! If you live in the tropics with outside temps in the 90*s an humidity in the 80+% range then it is heated up by the incubator to 99*. The warmer air can hold a little (very little) more water so it absorbs it from the eggs.

Same incubator running in cold dry desert. Outside air is in the 40*s with a relative humidity in the 10% to 20% range. The air comes in to the incubator an is heated up to 99*. The dry air is now hot, very dry air. It draws moisture from everything. If you dont give it moisture it will take it all from the eggs. So you add a lot of water. This does not stop moisture from being pull from the eggs but it slows it down. Even if you managed to get the humidity in the incubator up to 100%, that 100% moisture is coming from somewhere, an alot of it is from the eggs.An every time the air in the incubator replaces its self it pulls on that moisture again.

Most of us fall somewhere in between these two extremes so we add or take away water an we open or close vents to speed up or slow down air exchange an the speed moisture is carried out of the incubator.

So does the temp an humidity outside matter? Its the only thing that does matter. Everything else we do is to try to compensate for it.
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