Last winter was unusually cold for my area, with days turning to weeks of temperatures way below freezing.
My schedule allowed me to gather my eggs twice a day, 8am and 8pm.
For weeks I had cracked frozen eggs. Literally dozens of eggs were deemed unfit for human consumption, and fed back the the birds.
US FDA says:
"Shell eggs should not be frozen. If an egg accidentally freezes and the shell cracked during freezing, discard the egg. Keep any uncracked eggs frozen until needed; then thaw in the refrigerator. These can be hard cooked successfully but other uses may be limited. That's because freezing causes the yolk to become thick and syrupy so it will not flow like an unfrozen yolk or blend very well with the egg white or other ingredients."
My solution was to heat the nesting boxes (3 boxes in total).
Seedling heat mats. Each uses 17 watts. Water proof construction. UL listed.
I began by cleaning the 16" cube nesting box out completely.
I cut a 1" hole in the top of the box to insert the power cord of the seed mat.
Then installed mat to box using paint sticks and screws. The mat bends easily when warm.
I covered the mats with the leaf bags, a perfect fit at 16" width. Disposable when soiled.
I covered the leaf bags with shredded junk mail, easily replaced and plentiful, and inserted some ceramic eggs in each box
Connected the 3 boxes to the power cord extension
Connected the power cord extension to the power strip, which has the thermo cube and LED night light to show when thermo cube is powered on
The power strip is connected to the light timer, set to turn on at 5:30am, off at 9:00pm. Note that the power to the lights are on the first timer outlet, which first goes through a photocell, so lights only are only on when needed. All power comes from a GFIC outlet. All wiring is inaccessible to the flock.
The light timer supplies power on at 5:30am, off at 9:00pm.
The Thermo cube powers the mats only when temps reach below 35F, and off at 45F
The mats heat the nesting material to around 20 degrees above ambient temperatures.
The "Heated Nest Boxes" help keep the eggs from freezing till temperatures reach around 10F.
Hope this helps others!
We had an unusually cold February 2015 for my area, many day temperatures only in the teens.
My schedule allowed egg collection once around 8AM and once around 8PM.
My coldest recorded egg temperature was 33F, significantly above the 28F threshold for egg freezing.
That particular day, daytime high temperatures in the coop were in the low teens (13F), and the eggs were collected at 8:30pm, when ambient temperature was 11F and falling (nighttime lows reached below 0F, unusual for our area).
The heated nest boxes worked as designed, flawlessly!
I had 0 frozen eggs, whereas the previous year I had literally dozens...