My seedling mats are keeping the nests, and eggs, 19F degrees above ambient nest temperatures. The mats are fairly inexpensive as compared to other heat sources. This should (hoping) help keep eggs unfrozen to temps as low as 10F.
You know we had record breaking cold days in NJ last year. Too many frozen cracked eggs. This will help.
This will be my first winter with hens ... I just figured they stopped laying in the cold months ... apparently not then? I am also in NJ.
They may depending on breed and age. Most chickens require 12-14 hours of light to continue to lay. I posted this on another query, this is how I do it, works extremely well, hope it helps: There are a lot of opinions on supplementing light to keep the chickens laying during time period where there is less than 12-14 hours of available daylight. My coop gets 16 hours of light 351 days per year. I turn lights off for 14 days to have birds go into a controlled moult late September . Having had to install electricity for the thermostatically controlled water heater, I took advantage and installed a lighting system. My system has two timers. The first is set to turn the lights on at 5:30am, off at 9pm. Power goes on, passes through a photocell, then to a 300 lumen LED bulb, 4.8 watts, in the 8x8 foot print coop, and 2 4.8 watt LEDs for the 14x14 foot print outside run. I light the run because I found the birds huddled outside the coop door in the dark one 5:30am morning... They have access to the run 24/7, as it is as secure as the coop. The lights are on only when it is dark enough outside to be necessary. The time on very closely mimics my Summer Solstice in NJ. The second timer is set to go on at 8:30pm, off at 9:30pm, a diffused 200 lumen LED 4 watt bulb. This low light allows the birds to settle in before all lights out and 8 hours of darkness. This system costs less than $5 per year to operate.. Hope this helps.
Update: We have had an unusually cold February for my area, many day temperatures only in the teens. My schedule allows egg collection once around 8AM and once around 8PM. The heated nest boxes are working as designed, flawlessly! This year to date I have had 0 frozen eggs, whereas last year I had literally dozens... My coldest recorded egg temperatures was 33F, significantly above the 28F threshold for egg freezing. That particular day, daytime high temperatures in the coop were in the low teens, and the eggs were collected at 8:30pm.