Several years ago we were "gifted" a mature Welsummer rooster. We generally do not bring mature birds into our flock due to the risk of respiratory problems and other health-related issues but this rooster came from...well, we didn't have any choice (family). Since we now had a nice looking Welsummer rooster and we had several Welsummer hens, I made an off-hand comment to my wife about incubating and hatching a few eggs. Although we had kept chickens for years it was something we had never tried. When my wife realized that I was researching incubation and incubators, she went into the basement and plucked a Little Giant incubator out of her hoard. She had purchased it at a garage sale decades ago for $3.00 USD.
We hatched a lot of eggs with the Little Giant incubator. We added Welsummers, Silver Double Laced Barnevelders, Olive Eggers, and a bunch of barnyard crosses to our flock. We enjoyed hatching our own chicks. Every egg that did not develop was a disappointment, every chick that did not make it was a tragedy. The failures hurt. I knew that there were things I could do to improve the Little Giant so I started tinkering.
I may have gone a little overboard. I installed a low-speed 23 cfm fan, switched to an STC-1000 single-relay temperature controller backed up with an ITC-1000 dual-relay controller, which was backed up with a simple digital temperature gauge and two spirit thermometers. I added water injection and a SensorPush Wireless Thermometer/Hygrometer so I could monitor the incubator temperature and humidity on my phone. I placed the whole thing in an enclosure of 1.5" EPS foam board inside a 3/4" pine case. It was a cobbled-together, unsightly mess.
I could not control the incubator air temperature with precision or take eggshell temperature readings at all, since I had to disassemble the enclosure to take a reading. I could monitor the air temperature but the temperature graph from the SensorPush wireless thermometer (below) was driving me to distraction. The oscillating temperature was due to several factors: the resistance coil heat element in the Little Giant, the built-in one degree hysteresis (dead band) of the STC-1000 and ITC-1000 temperature controllers, and the SensorPush sensor I had placed in the automatic egg turner.
Like a cast-iron frying pan on a stove, the heating element in the incubator continued to radiate heat after the controller de-energized the circuit at the set point of 100 degrees, causing the temperature to “drift” well above the set point. I saw high temperatures between 101 and 102 degrees due to this thermal drift.
As the incubator cooled down the heating circuit would not re-energize until the temperature fell below 99 degrees due to the controllers built-in hysteresis or “dead band” of one degree. This one degree dead band is built into electronic control circuits like the STC-1000 and ITC-1000 to prevent rapid switching that may cause premature component failure. If the set point is 100 degrees, the controller provides an operating range of 99 to 101 degrees, one degree above the set point and one degree below the set point.
When the temperature in the incubator fell below 99 degrees the circuit would re-energize the heating element. The heating element would begin to warm up. During this warm-up period the incubator temperature would continue to fall until the heating element “caught up.” I saw low temperatures of around 98 degrees. Altogether I was seeing a cyclic temperature swing of more than 3.5 degrees Fahrenheit.
The biggest problem was the SensorPush Wireless Thermometer/Hygrometer I was using to monitor the incubator remotely. I could see the impact of thermal drift and controller dead band on my incubator temperature. The sensor was also graphing the movement of the egg turner. The small sensor fit perfectly in the egg turner, level with the top third of an incubating egg. As the 1/240 motor on the egg turner cycled the eggs through a 90 degree arc six times every 24 hours (45 degrees right, 45 degrees left), the SensorPush software graphed the movement of the sensor. The 23 cfm fan circulating air within the incubator should have eliminated temperature stratification but as the sensor moved through its arc in the egg turner the SensorPush was clearly graphing six complete cycles every 24 hours. I love precise data but watching the graph rise and fall was very stressful.
It was time to figure out a better way of doing things. I retired the venerable but maddening Little Giant incubator and started researching. I read all sorts of message boards and watched many, many YouTube videos. "Refrig-r-bators" were very popular but I wanted to see inside the incubator without opening the door, although watching eggs in an incubator is about as exciting as watching paint dry.
I started looking for a glass-door beverage cooler that was at least 16" wide and 16" deep inside so I could continue to use my automatic egg turners. I eventually came across a non-working GE Monogram beverage cooler on Craigslist. The GE Monogram has a 6.6 cu.ft. steel cabinet that is 20" wide x 20" deep inside so my automatic egg turner(s) would easily fit inside. The Monogram also has a dual-pane glass door so I would be able to see inside. The white plastic interior is backed by 1/8" aluminum, which is surrounded by 1.75" of polyisocyanurate insulation. Perfect.
I removed the glass door while I was modifying the cabinet. The door was surprisingly heavy, and without the door I could easily flip the cabinet upside down or lay it on any side to work on it. It really helped, especially when I was applying the foil tape. I had no use for the original thermostat behind the control faceplate but I left it in place, disconnected, simply because it held the control knob on the faceplate. I retained the door light and door light rocker switch, which still work, but I removed the sliding drawers because I could not figure out a use for them. I removed the compressor but was careful to retain all of the cabinet wiring. I saved the 120V AC cooling fan, thinking I might find a use for it later.
For a heat source I wanted something long-lasting, foolproof, and 100% reliable. As I researched do-it-yourself and homemade incubators I quickly learned that people who keep and raise reptiles, especially those who keep and raise frogs and amphibians, are extremely good at temperature and humidity control. Rather than reinvent the wheel I would use what they used, THG heat tape from Pangea Reptile. The 12" wide, 23 watt per foot THG heat tape produces an even heat across the width when energized and has very little thermal mass so I would not have excessive thermal drift within the enclosure. THG heat tape has no moving parts, no filaments to burn out, and no glowing coils to worry about. Herpetology buffs in the USA use THG and FlexWatt heat tapes almost exclusively for their incubators, enclosures, and reptile racks.
I got ahead of myself and installed the THG heat tape without taking photos of the process but installing the heat tape was very simple. The tape is flexible and can be cut to length with scissors between the black "bars." I flipped the cabinet upside and centered the heat tape in the enclosure. Using small pieces of Scotch tape I taped the heat tape in place, flipping the cabinet as I worked so that the area I was working on was always "down." This made installing the heat tape much easier since it was always laying flat on the side I was working on. When I had it where I wanted it I went back and taped the edges down permanently with foil tape, being careful not to cover the copper strips on either side. I have seen a installations where the copper strips are covered by the foil tape (not recommended) but leaving the copper uncovered looks nice.
After checking the wire gauge to make sure it would work with the heat tape I used the original thermostat wiring behind the front control faceplate to connect the THG heat tape, through the cabinet wiring, to a power cord in the back of the cabinet. Using the wiring already built into the cabinet made for a very clean installation. The heat tape power cord will plug into a thermostat/temperature controller. By starting the heat tape at the top and going back then down and across the bottom, I was able to fit just under 60" of tape inside, which gave me 115 watts of heat. According to my calculations I needed 82 watts to heat my cabinet so I had a fairly large "reserve" of 33 watts.
I replaced the original glass shelves with powder-coated wire shelving for better air circulation within the cabinet. The 20" wide x 16" deep wire shelves slid easily into place after I cut them to length from a single 8' shelf I purchased at a home improvement store. I used wire shelving for three reasons: first, the wire shelving will not impede air circulation within the enclosure. Second, I wanted to be able to easily sterilize every part of my incubator, including the shelves. Third, I did not want shelves made out of 2x4's and hardware cloth in my incubator.
I did not want power cords dangling out of the door or run through random holes in the cabinet so I installed two 120V duplex outlets inside the enclosure to run the automatic egg turners and circulation fans. I carefully cut holes through the plastic interior liner and 1/8" aluminum wall behind the liner with my oscillating tool, removed just enough of the polyisocyanurate insulation to account for the duplex outlets, and ran my wiring through the middle of the insulation into the space formerly occupied by the compressor.
I was able to do my modifications without tearing into the back by running my wiring through the middle of the 1.75" thick polyisocyanurate insulation that surrounds the cabinet to a 2-gang junction box installed in the space formerly occupied by the compressor. A grounded 3-prong electrical cord from the junction box powers everything, including the extra duplex outlet I installed on the side of the cabinet. By installing the extra outlet on the side I can fit the incubator close against the wall rather than having it "stand off" the wall due to cords I may want to plug into it. I didn't think I would actually use the additional outlet but I plugged an additional device into it almost immediately.
I addressed air circulation within the enclosure by reusing the 80mm x 38mm fan I had installed in the Little Giant incubator. I mounted the fan on a polished aluminum bracket I made out of piece cut from an old STOP sign. After watching the incubator operate in test-mode for a couple days I decided that I needed additional air circulation inside. Unfortunately I had eggs on the way so I took the 120V cooling fan I removed when I gutted the compressor compartment and temporarily mounted it low inside the cabinet blowing upward. Before I incubate another setting I will replace the single 80mm x 38mm fan with three 80mm x 25mm fans and remove the temporarily installed 120V fan.
For ventilation I drilled a 1.125" exhaust hole in the top and another 1.125" intake hole in the bottom, then covered the holes with black stainless steel vent covers.
I need to replenish oxygen and get rid of carbon dioxide and excess humidity but the actual volume of air exchange required is very small. An developing egg needs 0.143 cubic feet of fresh air at 20.95% oxygen concentration per day by Day 18 of incubation, so if I am incubating 24 eggs I need 3.4 cu.ft. of fresh air per day by Day 18. My incubator has a volume of 6.6 cu.ft., so I need to exchange half the volume of air inside the cabinet every day by Day 18. The image below shows the flow of warm air through the top vent (vent cover removed). As warm air rises through the top vent, fresh air is drawn into the incubator through the bottom vent.
Carbon dioxide (CO2) is the least of my worries. The average carbon dioxide content of fresh air is ~400 ppm (parts per million). The CO2 concentration under a hen sitting on eggs has been measured at more than 4000 ppm. If Nature can make it work under a hen at 10 times the normal atmospheric concentration of carbon dioxide I am not at all concerned about carbon dioxide buildup in my small-scale incubator.
I did not use my STC-1000 or ITC-1000 for temperature control. The STC-1000 is a very popular device and countless eggs have been successfully hatched using the STC-1000 for temperature control, but there are several things about the STC-1000 and ITC-1000 that I do not like. First, the STC and ITC controllers are basically "dumb" thermostatically controlled switches. They are either ON or OFF, applying full power or no power to the heating element. I wanted precise, proportional control. Second, I wanted to be able to control the incubator temperature to one-tenth of a degree, and I could only set the STC and ITC controllers in one-degree increments. The inability to set a digital temperature controller to a tenth of a degree was extremely annoying. Third, I did not like the built-in deadband (hysteresis) of one degree, which gave me an actual operating range of one degree above the set point to one degree below the set point. There was just no way to achieve precision temperature control.
I considered using a proportional–integral–derivative or "PID" controller. PID controllers are "smart" devices that automatically correct control functions, like cruise control in a car. Home-brewers and distillers use PID controllers extensively, and there are many people who use PID controllers in their incubators, but the reviews of specific PID controllers were not all that great.
I eventually narrowed temperature control down to either a Vivarium VE-200 from Reptile Basics or a Spyder Robotics Herpstat 1 from Pangea Reptile. I purchased the Spyder Robotics Herpstat 1. The Herpstat 1 is a single output, dual mode, proportional controller that runs an auto power-matching algorithm to constantly adjust the power output for the best regulation possible. With the Herpstat 1 I can control my incubator air temperature to one-tenth of one degree.
My decision to purchase the Herpstat 1 rather than reuse the STC or ITC temperature controller brought the cost up significantly but in my opinion the temperature controller is the most important component in the incubator. With the Herpstat I can control the air temperature within my incubator to one-tenth of one degree, quickly take daily eggshell temperature readings, and easily adjust the temperature controller to achieve optimum incubator performance.
On D18 I swap out the automatic egg turner shelf (the egg turner is zip-tied to the wire shelf) for hatching baskets. I use water pans on D20 to raise the humidity. In a smaller incubator the relative humidity will go up naturally during hatch. At 6.6 cubic feet my incubator interior volume is simply too large for the modest number of eggs I typically incubate. If I had a smaller incubator I would dry incubate and dry hatch.
If I had reused the STC-1000 or ITC-1000 temperature controller the total cost of the build would have been slightly over $100 USD:
- GE Monogram beverage cooler, $20
- Wire shelf, 8' x 16" $18
- THG heat tape, 12" $21
- STC-1000 or ITC-1000 temperature controller, $15.99
- 80mm case fan, $15
- (3) Black stainless steel vent louvers, $4.99
- (3) duplex outlets @ $.83/ea., $2.49
- (3) duplex outlet covers @ $.28/ea., $.84
- 2-gang junction box, $.72
- 2-gang junction box cover, $.62
- (4) 3/8" conduit clamps @ $.43/ea., $1.72
- miscellaneous wiring, wire nuts, screws, etc collected from around the shop.
Building a Custom Glass Door Incubator
Build your own custom high-capacity incubator!