Humidity problem

[crt]

I've built myself an incubator for hens' eggs which holds a pretty steady temperature, and has an automatic turner.

However I'm really struggling with humidity. When the room temp is c.15 deg C and room relative humidity is 70-75% (west of England, mid-May), incubator humidity won't go above 40-45%, even with a tray of water with a surface area the almost the same as the floor area of the incubator (300mmx400mm). I can get the level up to 75% by putting a soaked tea towel across the bottom of the incubator, under the eggs, for the last three days but this means constantly opening and shutting the lid and moving the eggs to dampen the cloth which I would like to avoid.

Added to this, my last hatch was dismal with only three hatched chicks out of 19 fertile (22 originally), starting at day 23/4, last one day 25/6, with about 12 of the remainder fully formed and dead in shell (no pipping). Confusingly the air gap in the shells looked pretty small which suggests if anything humidity too high. (Late hatch might be due to temp being slightly low but I wonder whether this could be humidity related as the incubator shows a steady 37.7 just above the eggs (with fans), so would only be a fraction less below).

I use a digital hygrometer which is accurate to +/- 10% when calibrated against a wet bulb thermometer at room temp/r-h.

Anyone have any suggestions?

Thank you.

 

[chrismahon]

Hi Crt. If the humidity is high in the room you can run the incubator dry for the first 18 days. When I say dry I mean no water in it. The electric heating has a 'drying' effect on the air, hence the difference you are seeing. Could be the air gap was too small to let them pip. Then raise to 60% after first pipping. You may find that a small pot with a piece of sponge floating in it may be enough to increase the surface area for evaporation, as that's what you need to raise the humidity. Opening the incubator after first pipping is not good though.

 

[crt]

Thanks. That"s interesting, I had always understood I should be looking at the R/H in the incubator being at c50% in the first 18 days, and the physics of humidity being what it is, the higher the temperature, the lower the humidity (other things being equal).

 

[chrismahon]

A lot of people run their incubators dry Crt. The ultimate test is the size of the air sac over time. The eggs can be weighed as a group and the average weight used - any discarded due to infertility after candling are assumed to be of average weight, so the new average arrives from less eggs. Can't say taking eggs out is a good thing, certainly not in the first 7 days. Then the humidity is raised after pipping to stop the chick sticking to the membrane and the incubator should not be opened in case the humidity drops and takes too long to recover, as well as the temperature drop.

 

[Chuck]

I am thinking along the same lines as Chris on this one. 50% humidity for the first 18 days is much higher than I would aim for. No need for 75% at hatching either, 60% max is enough. 35-40% in the first 18 days is what I aim for and is achieved by running it without water only increasing the humidity when the first eggs chip. That your air gaps are small suggests that there has not been enough evaporation from the eggs.
Leaving out the theory, in practical terms there are many of us who discovered that by running on lower humidities, we had much better hatch rates and this applies to a variety of incubators. Most of us tried this metheod in frustration at getting poor results sticking to the instructions.

 

[crt]

thanks for all that advice. I've set up another batch and will follow the guidance and see what happens.

 

[crt]

Just to update you, the last lot hatched this week with 10 live out of 20 set bang on 21 days, four infertile at seven days and the remaining six still not doing much at 24 days. So, compared to my previous attempts an excellent result, and thank you for the sound advice.