rebelcowboysnb has some good advice on how to make a water heater t-stat work well. Many have used them very successfully. What's important to remember about them is that they're designed to have a fairly wide temperature swing. I think it's about 6*F usually. If you have it set at 100*F it will kick on at 97*F and off again at 103*F. This seems to make a lot of folks nervous.
What one has to remember is that the 6*F swing is in air temperature, not a solid (or semi-solid) mass like an egg. Measuring the temperature with an egg-o-meter or water wiggler will reveal that the temperature of a solid or liquid remains far more stable throughout the swing in air temp. If you add thermal mass to your incubator it becomes even more stable. For instance, I just built an incubator out of rigid styrofoam board and lined it with ceramic tile. There is also a quart jar of water in there for mass as well. My air temperature varies b/t 98*F and 102.5*F with a constant temp of 100.5*F in the water wiggler. Truth be told, the biggest trouble I have is in fine adjustment on the water heat t-stat. Getting it from 100.5*F to 99.5*F has been a little challenging, but I'm not really stressing over it.
What one has to remember is that the 6*F swing is in air temperature, not a solid (or semi-solid) mass like an egg. Measuring the temperature with an egg-o-meter or water wiggler will reveal that the temperature of a solid or liquid remains far more stable throughout the swing in air temp. If you add thermal mass to your incubator it becomes even more stable. For instance, I just built an incubator out of rigid styrofoam board and lined it with ceramic tile. There is also a quart jar of water in there for mass as well. My air temperature varies b/t 98*F and 102.5*F with a constant temp of 100.5*F in the water wiggler. Truth be told, the biggest trouble I have is in fine adjustment on the water heat t-stat. Getting it from 100.5*F to 99.5*F has been a little challenging, but I'm not really stressing over it.
