It was actually quite effective, but after much tinkering and testing over the last two years, I've made some adjustments that I believe have made a significant improvement in the design.
Key Changes:
First off, the cooler I used in the first version was good, but I've found an even better one. There is a HUGE difference between those thin walled (3/4-1 inch) foam coolers and the heavy duty ones that are used for shipping perishable medical supplies. Yes, there are some thin walled ones that are used by pharmacies and pharmaceutical companies for overnight shipments, but there are also some very heavy duty foam coolers out there. I honestly don't know what the one I found was intended for, but the walls are a solid 1.75 inches thick, and made from very dense, strong foam. I would say that if you can't find something with at least 1.25 inch thick sides and bottom, you're going to have to do something to improve its insulating ability, and that's a huge pain in the butt. Alternatively, keep it in a warm, climate controlled room. Mine stays in the garage all spring, and it still maintains temperature easily even when temps in the garage get down into the 20s F. Your best bet for finding a good one is to talk to someone who works at a hospital, clinic, or who gets medicine shipped to them.
Ideally, your cooler should be as small as it can be to hold the number of eggs you want to hatch and fit the light and fan and water bowl in. Bigger incubators have less stable temperature and humidity. I have tested designs as large as 24"x24"x36" and they just don't hold a stable temperature without a much more involved heating and air circulation setup than what you can use in the small ones.It's impossible to underestimate the importance of insulation. Large temperature swings outside the incubator WILL impact the temperature and humidity inside the incubator, despite your best efforts and a good thermostat, and the larger the incubator, the more pronounced this effect will be.
Keep the window small. I made this same mistake in this version as well (partly because I didn't have a smaller piece of glass), and I've learned that the window loses so much heat from the incubator that I actually cover it with a 2 inch thick piece of foam when I'm not actually looking through it.
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| Chicks hatched from my DIY incubator. |
Lessons learned:
Spend the money on a high quality 40w light bulb if you're going to have the incubator someplace where it isn't nice and warm. If mine was in my house I'd go to a 25w bulb, but the 40 ensures that I hold temp even if it gets down to 20F overnight. You want the candle style bulb, so that you can fit it through the hole that the light fixture sits in. You can change the bulb in the event of a burnout without completely emptying the incubator this way.
Keep a spare bulb on hand at all times. A burned out bulb can cost you the whole batch in just a few hours. This is why quality bulbs are important. Don't skimp on this part.
The eggs should always be above the heat source, on a shelf/rack made of 1/4 inch wire mesh, or something similar. I've seen a few designs recently where the eggs sit on the floor of the incubator next to the heat source. I've tried this and I guarantee you that few if any eggs will hatch. There is insufficient air circulation to ensure thorough mixing and thus even temperatures throughout the eggs.
If you can, get a hygrometer. Yes you can learn what is correct humidity through trial and error, but it's easier if you don't have to. If you insist on learning it the hard way, here's a suggestion as a starting point. use a bowl about 1/12 the size of the floor of the incubator full of water for the first 17 days. This should get you close to the necessary 40% humidity. On day 18, pour a very thin layer (about 1/16 inch deep) of water right on the floor of the incubator, and also refill the bowl. Do not cover the whole floor, you just want to increase the surface area of water by about 4x. This will probably cause the humidity to climb to near 100% at first, so a few hours after doing this, lift the lid just slightly and let some of that extra water out. After this, do not add more water. So long as you're not opening the lid constantly, the humidity should stay about right - 70% or so - until day 22 (or 23) when you should be removing chicks and removing failed eggs.
If the fan seems a little too big, it's probably about right. You need a lot of airflow to make sure that no areas of dead air form in or around the eggs. A 3-4" computer fan seems to work pretty well in an incubator that holds 20-30 eggs. I've tried smaller 1.5 inch fans and they are clearly inferior for this purpose. The fan should also be towards the top of the incubator, opposite the heat source. This makes it so the fan is forcing air down and around the light, spreading the heated air out under the eggs, leading to more even heating, and also avoiding a hot spot directly above the light, which could burn those eggs nearest the bulb.
All the literature says the best temperature in a moving air incubator is 99.5. I've done a fair amount of research on this, and I have decided to set my thermostat so that as it cycles, it averages about 100.0 F. This is partly because developing eggs are less tolerant of temperatures below 98 than they are of temperatures above 103. Using 100.0 F puts me right in the middle of their temperature tolerance, keeping a little more cushion against the lower temperatures that happen if a bulb burns out or you lose power. That extra .5 degrees can mean as much as a half hour of time for you to catch such a problem. It also accelerates the hatch by about 10 hours, by my best guess.
Conclusions:
After much tinkering, many successes and almost as many failures, I've worked out a design and system that is currently achieving an 86% hatch rate. I candle on day 7 and discard the clear eggs (infertile or failed to develop at all) and the last batch that just finished, 8 out of 9 eggs hatched on day 21, and the batch before that, 11 out of 13 on day 21 or early on day 22.
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