Can you post some pics on here to see what you are working with.. such as what kind of thermostat your using and what is your heat source and how many vents you have.. everything has an impact on how well it holds temp.. is it made from scratch from wood or is it something you turned into a bator .. like i said more info is needed to try and give you some help.. but i would not want that much of a temp swing .. from they amount of temp diff it sounds like you are using a waterheater thermostat.. in my experience which im no expert by any means but i have built a few bators and hatchers and i did try the waterheater thermostat but i did not care for the temp diff. maybe im a little picky but for a few more bucks you can use a wafer thermostat and they work way better.. i use a wafer in the hatcher im using now and i have a digital thermostat in my bator.. but anyway we could help you more if you posted pics and more info...