I've been using the Little Giant 9300 incubators for hatching quail. My last few hatches had lower hatch rates. I had moved my incubators into a different room. one without a door. So it could be drafty. So I moved them back to the room I used before. Well, my last two hatches? nothing. Now during this time I had purchased a programmable thermostat for the house heating and air. And I'm very conservative with my electric. My incubators were having major temp swings. So I got a small space heater that had an adjustable thermostat that I set on 70. now I have steadier temps in my LGs. I hope to build a wooden cabinet incubator, and also try making one from a mini refrigerator, if I can get the right dimensions as I want to use my egg turners.
So far I haven't tried incubating chickens. But as soon we get a few more duck eggs they're going in.
Friend
Educator
Spirit
Greeter
Kenny
If you type in diy incubators in the search above there should be threads on them that come up. I cheated and bought an incubator to satisfy my addiction!! Will this be your first incubation? It sure can become addictive once you get started incubating eggs. It's lots of fun amd very rewarding as you see your new chicks hatch. 
